Tutorials

• 1: Hello Minikube
• 2: Learn Kubernetes Basics
• 2.1: Create a Cluster
• 2.1.1: Using Minikube to Create a Cluster
• 2.2: Deploy an App
• 2.2.1: Using kubectl to Create a Deployment
• 2.3: Explore Your App
• 2.3.1: Viewing Pods and Nodes
• 2.4: Expose Your App Publicly
• 2.4.1: Using a Service to Expose Your App
• 2.5: Scale Your App
• 2.5.1: Running Multiple Instances of Your App
• 2.6: Update Your App
• 2.6.1: Performing a Rolling Update
• 3: Configuration
• 3.1: Example: Configuring a Java Microservice
• 3.1.1: Externalizing config using MicroProfile, ConfigMaps and Secrets
• 3.2: Configuring Redis using a ConfigMap
• 4: Security
• 4.1: Apply Pod Security Standards at the Cluster Level
• 4.2: Apply Pod Security Standards at the Namespace Level
• 4.3: Restrict a Container's Access to Resources with AppArmor
• 4.4: Restrict a Container's Syscalls with seccomp
• 5: Stateless Applications
• 5.1: Exposing an External IP Address to Access an Application in a Cluster
• 5.2: Example: Deploying PHP Guestbook application with Redis
• 6: Stateful Applications
• 6.1: StatefulSet Basics
• 6.2: Example: Deploying WordPress and MySQL with Persistent Volumes
• 6.3: Example: Deploying Cassandra with a StatefulSet
• 6.4: Running ZooKeeper, A Distributed System Coordinator
• 7: Services
• 7.1: Connecting Applications with Services
• 7.2: Using Source IP
• 7.3: Explore Termination Behavior for Pods And Their Endpoints

1 - Hello Minikube

This tutorial shows you how to run a sample app on Kubernetes using minikube. The tutorial provides a container image that uses NGINX to echo back all the requests.

Objectives

• Deploy a sample application to minikube.
• Run the app.
• View application logs.

Before you begin

This tutorial assumes that you have already set up minikube. See Step 1 in minikube start for installation instructions.

You also need to install kubectl. See Install tools for installation instructions.

Create a minikube cluster

minikube start

Open the Dashboard

Open the Kubernetes dashboard. You can do this two different ways:

• Launch a browser
• URL copy and paste

# Start a new terminal, and leave this running.
minikube dashboard

# Start a new terminal, and leave this running.
minikube dashboard --url

Create a Deployment

A Kubernetes Pod is a group of one or more Containers, tied together for the purposes of administration and networking. The Pod in this tutorial has only one Container. A Kubernetes Deployment checks on the health of your Pod and restarts the Pod's Container if it terminates. Deployments are the recommended way to manage the creation and scaling of Pods.

1. Use the kubectl create command to create a Deployment that manages a Pod. The Pod runs a Container based on the provided Docker image.

   # Run a test container image that includes a webserver
   kubectl create deployment hello-node --image=registry.k8s.io/e2e-test-images/agnhost:2.39 -- /agnhost netexec --http-port=8080
   

2. View the Deployment:

   kubectl get deployments
   

   The output is similar to:

   NAME         READY   UP-TO-DATE   AVAILABLE   AGE
   hello-node   1/1     1            1           1m
   

3. View the Pod:

   kubectl get pods
   

   The output is similar to:

   NAME                          READY     STATUS    RESTARTS   AGE
   hello-node-5f76cf6ccf-br9b5   1/1       Running   0          1m
   

4. View cluster events:

   kubectl get events
   

5. View the kubectl configuration:

   kubectl config view
   

6. View application logs for a container in a pod.

   kubectl logs hello-node-5f76cf6ccf-br9b5
   

   The output is similar to:

   I0911 09:19:26.677397       1 log.go:195] Started HTTP server on port 8080
   I0911 09:19:26.677586       1 log.go:195] Started UDP server on port  8081
   

Create a Service

By default, the Pod is only accessible by its internal IP address within the Kubernetes cluster. To make the hello-node Container accessible from outside the Kubernetes virtual network, you have to expose the Pod as a Kubernetes Service.

1. Expose the Pod to the public internet using the kubectl expose command:

   kubectl expose deployment hello-node --type=LoadBalancer --port=8080
   

   The --type=LoadBalancer flag indicates that you want to expose your Service outside of the cluster.

   The application code inside the test image only listens on TCP port 8080. If you used kubectl expose to expose a different port, clients could not connect to that other port.

2. View the Service you created:

   kubectl get services
   

   The output is similar to:

   NAME         TYPE           CLUSTER-IP      EXTERNAL-IP   PORT(S)          AGE
   hello-node   LoadBalancer   10.108.144.78   <pending>     8080:30369/TCP   21s
   kubernetes   ClusterIP      10.96.0.1       <none>        443/TCP          23m
   

   On cloud providers that support load balancers, an external IP address would be provisioned to access the Service. On minikube, the LoadBalancer type makes the Service accessible through the minikube service command.

3. Run the following command:

   minikube service hello-node
   

   This opens up a browser window that serves your app and shows the app's response.

Enable addons

The minikube tool includes a set of built-in addons that can be enabled, disabled and opened in the local Kubernetes environment.

1. List the currently supported addons:

   minikube addons list
   

   The output is similar to:

   addon-manager: enabled
   dashboard: enabled
   default-storageclass: enabled
   efk: disabled
   freshpod: disabled
   gvisor: disabled
   helm-tiller: disabled
   ingress: disabled
   ingress-dns: disabled
   logviewer: disabled
   metrics-server: disabled
   nvidia-driver-installer: disabled
   nvidia-gpu-device-plugin: disabled
   registry: disabled
   registry-creds: disabled
   storage-provisioner: enabled
   storage-provisioner-gluster: disabled
   

2. Enable an addon, for example, metrics-server:

   minikube addons enable metrics-server
   

   The output is similar to:

   The 'metrics-server' addon is enabled
   

3. View the Pod and Service you created by installing that addon:

   kubectl get pod,svc -n kube-system
   

   The output is similar to:

   NAME                                        READY     STATUS    RESTARTS   AGE
   pod/coredns-5644d7b6d9-mh9ll                1/1       Running   0          34m
   pod/coredns-5644d7b6d9-pqd2t                1/1       Running   0          34m
   pod/metrics-server-67fb648c5                1/1       Running   0          26s
   pod/etcd-minikube                           1/1       Running   0          34m
   pod/influxdb-grafana-b29w8                  2/2       Running   0          26s
   pod/kube-addon-manager-minikube             1/1       Running   0          34m
   pod/kube-apiserver-minikube                 1/1       Running   0          34m
   pod/kube-controller-manager-minikube        1/1       Running   0          34m
   pod/kube-proxy-rnlps                        1/1       Running   0          34m
   pod/kube-scheduler-minikube                 1/1       Running   0          34m
   pod/storage-provisioner                     1/1       Running   0          34m
   
   NAME                           TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)             AGE
   service/metrics-server         ClusterIP   10.96.241.45    <none>        80/TCP              26s
   service/kube-dns               ClusterIP   10.96.0.10      <none>        53/UDP,53/TCP       34m
   service/monitoring-grafana     NodePort    10.99.24.54     <none>        80:30002/TCP        26s
   service/monitoring-influxdb    ClusterIP   10.111.169.94   <none>        8083/TCP,8086/TCP   26s
   

4. Check the output from metrics-server:

   kubectl top pods
   

   The output is similar to:

   NAME                         CPU(cores)   MEMORY(bytes)   
   hello-node-ccf4b9788-4jn97   1m           6Mi             
   

   If you see the following message, wait, and try again:

   error: Metrics API not available
   

5. Disable metrics-server:

   minikube addons disable metrics-server
   

   The output is similar to:

   metrics-server was successfully disabled
   

Clean up

Now you can clean up the resources you created in your cluster:

kubectl delete service hello-node
kubectl delete deployment hello-node

Stop the Minikube cluster

minikube stop

Optionally, delete the Minikube VM:

# Optional
minikube delete

If you want to use minikube again to learn more about Kubernetes, you don't need to delete it.

Conclusion

This page covered the basic aspects to get a minikube cluster up and running. You are now ready to deploy applications.

What's next

• Tutorial to deploy your first app on Kubernetes with kubectl.
• Learn more about Deployment objects.
• Learn more about Deploying applications.
• Learn more about Service objects.

2 - Learn Kubernetes Basics

Kubernetes Basics

This tutorial provides a walkthrough of the basics of the Kubernetes cluster orchestration system. Each module contains some background information on major Kubernetes features and concepts, and a tutorial for you to follow along.

Using the tutorials, you can learn to:

• Deploy a containerized application on a cluster.
• Scale the deployment.
• Update the containerized application with a new software version.
• Debug the containerized application.

What can Kubernetes do for you?

With modern web services, users expect applications to be available 24/7, and developers expect to deploy new versions of those applications several times a day. Containerization helps package software to serve these goals, enabling applications to be released and updated without downtime. Kubernetes helps you make sure those containerized applications run where and when you want, and helps them find the resources and tools they need to work. Kubernetes is a production-ready, open source platform designed with Google's accumulated experience in container orchestration, combined with best-of-breed ideas from the community.

Kubernetes Basics Modules

1. Create a Kubernetes cluster

2. Deploy an app

3. Explore your app

4. Expose your app publicly

5. Scale up your app

6. Update your app

2.1 - Create a Cluster

Learn about Kubernetes cluster and create a simple cluster using Minikube.

2.1.1 - Using Minikube to Create a Cluster

2.2 - Deploy an App

2.2.1 - Using kubectl to Create a Deployment

2.3 - Explore Your App

2.3.1 - Viewing Pods and Nodes

2.4 - Expose Your App Publicly

2.4.1 - Using a Service to Expose Your App

http://127.0.0.1:51082
!  Because you are using a Docker driver on darwin, the terminal needs to be open to run it.

2.5 - Scale Your App

2.5.1 - Running Multiple Instances of Your App

Objectives

• Scale an app using kubectl.

Scaling an application

Previously we created a Deployment, and then exposed it publicly via a Service. The Deployment created only one Pod for running our application. When traffic increases, we will need to scale the application to keep up with user demand.

If you haven't worked through the earlier sections, start from Using minikube to create a cluster.

Scaling is accomplished by changing the number of replicas in a Deployment.

Summary:

• Scaling a Deployment

You can create from the start a Deployment with multiple instances using the --replicas parameter for the kubectl create deployment command

Note:

If you are trying this after the previous section, you may have deleted the Service exposing the Deployment. In that case, please expose the Deployment again using the following command:

kubectl expose deployment/kubernetes-bootcamp --type="NodePort" --port 8080

Scaling overview

Previous Next

Scaling out a Deployment will ensure new Pods are created and scheduled to Nodes with available resources. Scaling will increase the number of Pods to the new desired state. Kubernetes also supports autoscaling of Pods, but it is outside of the scope of this tutorial. Scaling to zero is also possible, and it will terminate all Pods of the specified Deployment.

Running multiple instances of an application will require a way to distribute the traffic to all of them. Services have an integrated load-balancer that will distribute network traffic to all Pods of an exposed Deployment. Services will monitor continuously the running Pods using endpoints, to ensure the traffic is sent only to available Pods.

Scaling is accomplished by changing the number of replicas in a Deployment.

Once you have multiple instances of an application running, you would be able to do Rolling updates without downtime. We'll cover that in the next section of the tutorial. Now, let's go to the terminal and scale our application.

Scaling a Deployment

To list your Deployments, use the get deployments subcommand:

kubectl get deployments

The output should be similar to:

NAME                  READY   UP-TO-DATE   AVAILABLE   AGE
kubernetes-bootcamp   1/1     1            1           11m

We should have 1 Pod. If not, run the command again. This shows:

• NAME lists the names of the Deployments in the cluster.
• READY shows the ratio of CURRENT/DESIRED replicas
• UP-TO-DATE displays the number of replicas that have been updated to achieve the desired state.
• AVAILABLE displays how many replicas of the application are available to your users.
• AGE displays the amount of time that the application has been running.

To see the ReplicaSet created by the Deployment, run:

kubectl get rs

Notice that the name of the ReplicaSet is always formatted as [DEPLOYMENT-NAME]-[RANDOM-STRING]. The random string is randomly generated and uses the pod-template-hash as a seed.

Two important columns of this output are:

• DESIRED displays the desired number of replicas of the application, which you define when you create the Deployment. This is the desired state.
• CURRENT displays how many replicas are currently running.

Next, let’s scale the Deployment to 4 replicas. We’ll use the kubectl scale command, followed by the Deployment type, name and desired number of instances:

kubectl scale deployments/kubernetes-bootcamp --replicas=4

To list your Deployments once again, use get deployments:

kubectl get deployments

The change was applied, and we have 4 instances of the application available. Next, let’s check if the number of Pods changed:

kubectl get pods -o wide

There are 4 Pods now, with different IP addresses. The change was registered in the Deployment events log. To check that, use the describe subcommand:

kubectl describe deployments/kubernetes-bootcamp

You can also view in the output of this command that there are 4 replicas now.

Load Balancing

Let's check that the Service is load-balancing the traffic. To find out the exposed IP and Port we can use the describe service as we learned in the previous part of the tutorial:

kubectl describe services/kubernetes-bootcamp

Create an environment variable called NODE_PORT that has a value as the Node port:

export NODE_PORT="$(kubectl get services/kubernetes-bootcamp -o go-template='{{(index .spec.ports 0).nodePort}}')"

echo NODE_PORT=$NODE_PORT

Next, we’ll do a curl to the exposed IP address and port. Execute the command multiple times:

curl http://"$(minikube ip):$NODE_PORT"

We hit a different Pod with every request. This demonstrates that the load-balancing is working.

Note:

If you're running minikube with Docker Desktop as the container driver, a minikube tunnel is needed. This is because containers inside Docker Desktop are isolated from your host computer.

In a separate terminal window, execute:
minikube service kubernetes-bootcamp --url

The output looks like this:

http://127.0.0.1:51082
!  Because you are using a Docker driver on darwin, the terminal needs to be open to run it.

Then use the given URL to access the app:
curl 127.0.0.1:51082

Scale Down

To scale down the Deployment to 2 replicas, run again the scale subcommand:

kubectl scale deployments/kubernetes-bootcamp --replicas=2

List the Deployments to check if the change was applied with the get deployments subcommand:

kubectl get deployments

The number of replicas decreased to 2. List the number of Pods, with get pods:

kubectl get pods -o wide

This confirms that 2 Pods were terminated.

Once you're ready, move on to Performing a Rolling Update.

2.6 - Update Your App

2.6.1 - Performing a Rolling Update

Objectives

• Perform a rolling update using kubectl.

Updating an application

Users expect applications to be available all the time, and developers are expected to deploy new versions of them several times a day. In Kubernetes this is done with rolling updates. A rolling update allows a Deployment update to take place with zero downtime. It does this by incrementally replacing the current Pods with new ones. The new Pods are scheduled on Nodes with available resources, and Kubernetes waits for those new Pods to start before removing the old Pods.

In the previous module we scaled our application to run multiple instances. This is a requirement for performing updates without affecting application availability. By default, the maximum number of Pods that can be unavailable during the update and the maximum number of new Pods that can be created, is one. Both options can be configured to either numbers or percentages (of Pods). In Kubernetes, updates are versioned and any Deployment update can be reverted to a previous (stable) version.

Summary:

• Updating an app

Rolling updates allow Deployments' update to take place with zero downtime by incrementally updating Pods instances with new ones.

Rolling updates overview

Previous Next

Similar to application Scaling, if a Deployment is exposed publicly, the Service will load-balance the traffic only to available Pods during the update. An available Pod is an instance that is available to the users of the application.

Rolling updates allow the following actions:

• Promote an application from one environment to another (via container image updates)
• Rollback to previous versions
• Continuous Integration and Continuous Delivery of applications with zero downtime

If a Deployment is exposed publicly, the Service will load-balance the traffic only to available Pods during the update.

In the following interactive tutorial, we'll update our application to a new version, and also perform a rollback.

Update the version of the app

To list your Deployments, run the get deployments subcommand: kubectl get deployments

To list the running Pods, run the get pods subcommand:

kubectl get pods

To view the current image version of the app, run the describe pods subcommand and look for the Image field:

kubectl describe pods

To update the image of the application to version 2, use the set image subcommand, followed by the deployment name and the new image version:

kubectl set image deployments/kubernetes-bootcamp kubernetes-bootcamp=docker.io/jocatalin/kubernetes-bootcamp:v2

The command notified the Deployment to use a different image for your app and initiated a rolling update. Check the status of the new Pods, and view the old one terminating with the get pods subcommand:

kubectl get pods

Verify an update

First, check that the app is running. To find the exposed IP address and port, run the describe service command:

kubectl describe services/kubernetes-bootcamp

Create an environment variable called NODE_PORT that has the value of the Node port assigned:

export NODE_PORT="$(kubectl get services/kubernetes-bootcamp -o go-template='{{(index .spec.ports 0).nodePort}}')"
echo "NODE_PORT=$NODE_PORT"

Next, do a curl to the exposed IP and port:

curl http://"$(minikube ip):$NODE_PORT"

Every time you run the curl command, you will hit a different Pod. Notice that all Pods are now running the latest version (v2).

You can also confirm the update by running the rollout status subcommand:

kubectl rollout status deployments/kubernetes-bootcamp

To view the current image version of the app, run the describe pods subcommand:

kubectl describe pods

In the Image field of the output, verify that you are running the latest image version (v2).

Roll back an update

Let’s perform another update, and try to deploy an image tagged with v10:

kubectl set image deployments/kubernetes-bootcamp kubernetes-bootcamp=gcr.io/google-samples/kubernetes-bootcamp:v10

Use get deployments to see the status of the deployment:

kubectl get deployments

Notice that the output doesn't list the desired number of available Pods. Run the get pods subcommand to list all Pods:

kubectl get pods

Notice that some of the Pods have a status of ImagePullBackOff.

To get more insight into the problem, run the describe pods subcommand:

kubectl describe pods

In the Events section of the output for the affected Pods, notice that the v10 image version did not exist in the repository.

To roll back the deployment to your last working version, use the rollout undo subcommand:

kubectl rollout undo deployments/kubernetes-bootcamp

The rollout undo command reverts the deployment to the previous known state (v2 of the image). Updates are versioned and you can revert to any previously known state of a Deployment.

Use the get pods subcommand to list the Pods again:

kubectl get pods

Four Pods are running. To check the image deployed on these Pods, use the describe pods subcommand:

kubectl describe pods

The Deployment is once again using a stable version of the app (v2). The rollback was successful.

Remember to clean up your local cluster

kubectl delete deployments/kubernetes-bootcamp services/kubernetes-bootcamp

3 - Configuration

3.1 - Example: Configuring a Java Microservice

3.1.1 - Externalizing config using MicroProfile, ConfigMaps and Secrets

In this tutorial you will learn how and why to externalize your microservice’s configuration. Specifically, you will learn how to use Kubernetes ConfigMaps and Secrets to set environment variables and then consume them using MicroProfile Config.

Before you begin

Creating Kubernetes ConfigMaps & Secrets

There are several ways to set environment variables for a Docker container in Kubernetes, including: Dockerfile, kubernetes.yml, Kubernetes ConfigMaps, and Kubernetes Secrets. In the tutorial, you will learn how to use the latter two for setting your environment variables whose values will be injected into your microservices. One of the benefits for using ConfigMaps and Secrets is that they can be re-used across multiple containers, including being assigned to different environment variables for the different containers.

ConfigMaps are API Objects that store non-confidential key-value pairs. In the Interactive Tutorial you will learn how to use a ConfigMap to store the application's name. For more information regarding ConfigMaps, you can find the documentation here.

Although Secrets are also used to store key-value pairs, they differ from ConfigMaps in that they're intended for confidential/sensitive information and are stored using Base64 encoding. This makes secrets the appropriate choice for storing such things as credentials, keys, and tokens, the former of which you'll do in the Interactive Tutorial. For more information on Secrets, you can find the documentation here.

Externalizing Config from Code

Externalized application configuration is useful because configuration usually changes depending on your environment. In order to accomplish this, we'll use Java's Contexts and Dependency Injection (CDI) and MicroProfile Config. MicroProfile Config is a feature of MicroProfile, a set of open Java technologies for developing and deploying cloud-native microservices.

CDI provides a standard dependency injection capability enabling an application to be assembled from collaborating, loosely-coupled beans. MicroProfile Config provides apps and microservices a standard way to obtain config properties from various sources, including the application, runtime, and environment. Based on the source's defined priority, the properties are automatically combined into a single set of properties that the application can access via an API. Together, CDI & MicroProfile will be used in the Interactive Tutorial to retrieve the externally provided properties from the Kubernetes ConfigMaps and Secrets and get injected into your application code.

Many open source frameworks and runtimes implement and support MicroProfile Config. Throughout the interactive tutorial, you'll be using Open Liberty, a flexible open-source Java runtime for building and running cloud-native apps and microservices. However, any MicroProfile compatible runtime could be used instead.

Objectives

• Create a Kubernetes ConfigMap and Secret
• Inject microservice configuration using MicroProfile Config

Example: Externalizing config using MicroProfile, ConfigMaps and Secrets

Start Interactive Tutorial

3.2 - Configuring Redis using a ConfigMap

This page provides a real world example of how to configure Redis using a ConfigMap and builds upon the Configure a Pod to Use a ConfigMap task.

Objectives

• Create a ConfigMap with Redis configuration values
• Create a Redis Pod that mounts and uses the created ConfigMap
• Verify that the configuration was correctly applied.

Before you begin

You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. If you do not already have a cluster, you can create one by using minikube or you can use one of these Kubernetes playgrounds:

• Killercoda
• Play with Kubernetes

• The example shown on this page works with kubectl 1.14 and above.
• Understand Configure a Pod to Use a ConfigMap.

Real World Example: Configuring Redis using a ConfigMap

Follow the steps below to configure a Redis cache using data stored in a ConfigMap.

First create a ConfigMap with an empty configuration block:

cat <<EOF >./example-redis-config.yaml
apiVersion: v1
kind: ConfigMap
metadata:
  name: example-redis-config
data:
  redis-config: ""
EOF

Apply the ConfigMap created above, along with a Redis pod manifest:

kubectl apply -f example-redis-config.yaml
kubectl apply -f https://raw.githubusercontent.com/kubernetes/website/main/content/en/examples/pods/config/redis-pod.yaml

Examine the contents of the Redis pod manifest and note the following:

• A volume named config is created by spec.volumes[1]
• The key and path under spec.volumes[1].configMap.items[0] exposes the redis-config key from the example-redis-config ConfigMap as a file named redis.conf on the config volume.
• The config volume is then mounted at /redis-master by spec.containers[0].volumeMounts[1].

This has the net effect of exposing the data in data.redis-config from the example-redis-config ConfigMap above as /redis-master/redis.conf inside the Pod.

pods/config/redis-pod.yaml

apiVersion: v1
kind: Pod
metadata:
  name: redis
spec:
  containers:
  - name: redis
    image: redis:5.0.4
    command:
      - redis-server
      - "/redis-master/redis.conf"
    env:
    - name: MASTER
      value: "true"
    ports:
    - containerPort: 6379
    resources:
      limits:
        cpu: "0.1"
    volumeMounts:
    - mountPath: /redis-master-data
      name: data
    - mountPath: /redis-master
      name: config
  volumes:
    - name: data
      emptyDir: {}
    - name: config
      configMap:
        name: example-redis-config
        items:
        - key: redis-config
          path: redis.conf

Examine the created objects:

kubectl get pod/redis configmap/example-redis-config 

You should see the following output:

NAME        READY   STATUS    RESTARTS   AGE
pod/redis   1/1     Running   0          8s

NAME                             DATA   AGE
configmap/example-redis-config   1      14s

Recall that we left redis-config key in the example-redis-config ConfigMap blank:

kubectl describe configmap/example-redis-config

You should see an empty redis-config key:

Name:         example-redis-config
Namespace:    default
Labels:       <none>
Annotations:  <none>

Data
====
redis-config:

Use kubectl exec to enter the pod and run the redis-cli tool to check the current configuration:

kubectl exec -it redis -- redis-cli

Check maxmemory:

127.0.0.1:6379> CONFIG GET maxmemory

It should show the default value of 0:

1) "maxmemory"
2) "0"

Similarly, check maxmemory-policy:

127.0.0.1:6379> CONFIG GET maxmemory-policy

Which should also yield its default value of noeviction:

1) "maxmemory-policy"
2) "noeviction"

Now let's add some configuration values to the example-redis-config ConfigMap:

pods/config/example-redis-config.yaml

apiVersion: v1
kind: ConfigMap
metadata:
  name: example-redis-config
data:
  redis-config: |
    maxmemory 2mb
    maxmemory-policy allkeys-lru    

Apply the updated ConfigMap:

kubectl apply -f example-redis-config.yaml

Confirm that the ConfigMap was updated:

kubectl describe configmap/example-redis-config

You should see the configuration values we just added:

Name:         example-redis-config
Namespace:    default
Labels:       <none>
Annotations:  <none>

Data
====
redis-config:
----
maxmemory 2mb
maxmemory-policy allkeys-lru

Check the Redis Pod again using redis-cli via kubectl exec to see if the configuration was applied:

kubectl exec -it redis -- redis-cli

Check maxmemory:

127.0.0.1:6379> CONFIG GET maxmemory

It remains at the default value of 0:

1) "maxmemory"
2) "0"

Similarly, maxmemory-policy remains at the noeviction default setting:

127.0.0.1:6379> CONFIG GET maxmemory-policy

Returns:

1) "maxmemory-policy"
2) "noeviction"

The configuration values have not changed because the Pod needs to be restarted to grab updated values from associated ConfigMaps. Let's delete and recreate the Pod:

kubectl delete pod redis
kubectl apply -f https://raw.githubusercontent.com/kubernetes/website/main/content/en/examples/pods/config/redis-pod.yaml

Now re-check the configuration values one last time:

kubectl exec -it redis -- redis-cli

Check maxmemory:

127.0.0.1:6379> CONFIG GET maxmemory

It should now return the updated value of 2097152:

1) "maxmemory"
2) "2097152"

Similarly, maxmemory-policy has also been updated:

127.0.0.1:6379> CONFIG GET maxmemory-policy

It now reflects the desired value of allkeys-lru:

1) "maxmemory-policy"
2) "allkeys-lru"

Clean up your work by deleting the created resources:

kubectl delete pod/redis configmap/example-redis-config

What's next

• Learn more about ConfigMaps.

4 - Security

Security is an important concern for most organizations and people who run Kubernetes clusters. You can find a basic security checklist elsewhere in the Kubernetes documentation.

To learn how to deploy and manage security aspects of Kubernetes, you can follow the tutorials in this section.

4.1 - Apply Pod Security Standards at the Cluster Level

Pod Security is an admission controller that carries out checks against the Kubernetes Pod Security Standards when new pods are created. It is a feature GA'ed in v1.25. This tutorial shows you how to enforce the baseline Pod Security Standard at the cluster level which applies a standard configuration to all namespaces in a cluster.

To apply Pod Security Standards to specific namespaces, refer to Apply Pod Security Standards at the namespace level.

If you are running a version of Kubernetes other than v1.29, check the documentation for that version.

Before you begin

Install the following on your workstation:

• kind
• kubectl

This tutorial demonstrates what you can configure for a Kubernetes cluster that you fully control. If you are learning how to configure Pod Security Admission for a managed cluster where you are not able to configure the control plane, read Apply Pod Security Standards at the namespace level.

Choose the right Pod Security Standard to apply

Pod Security Admission lets you apply built-in Pod Security Standards with the following modes: enforce, audit, and warn.

To gather information that helps you to choose the Pod Security Standards that are most appropriate for your configuration, do the following:

1. Create a cluster with no Pod Security Standards applied:

   kind create cluster --name psa-wo-cluster-pss
   

   The output is similar to:

   Creating cluster "psa-wo-cluster-pss" ...
   ✓ Ensuring node image (kindest/node:v1.29.2) 🖼
   ✓ Preparing nodes 📦
   ✓ Writing configuration 📜
   ✓ Starting control-plane 🕹️
   ✓ Installing CNI 🔌
   ✓ Installing StorageClass 💾
   Set kubectl context to "kind-psa-wo-cluster-pss"
   You can now use your cluster with:
   
   kubectl cluster-info --context kind-psa-wo-cluster-pss
   
   Thanks for using kind! 😊
   

2. Set the kubectl context to the new cluster:

   kubectl cluster-info --context kind-psa-wo-cluster-pss
   

   The output is similar to this:

   Kubernetes control plane is running at https://127.0.0.1:61350
   
   CoreDNS is running at https://127.0.0.1:61350/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy
   
   To further debug and diagnose cluster problems, use 'kubectl cluster-info dump'.
   

3. Get a list of namespaces in the cluster:

   kubectl get ns
   

   The output is similar to this:

   NAME                 STATUS   AGE
   default              Active   9m30s
   kube-node-lease      Active   9m32s
   kube-public          Active   9m32s
   kube-system          Active   9m32s
   local-path-storage   Active   9m26s
   

4. Use --dry-run=server to understand what happens when different Pod Security Standards are applied:

   1. Privileged

      kubectl label --dry-run=server --overwrite ns --all \
      pod-security.kubernetes.io/enforce=privileged
      

      The output is similar to:

      namespace/default labeled
      namespace/kube-node-lease labeled
      namespace/kube-public labeled
      namespace/kube-system labeled
      namespace/local-path-storage labeled
      

   2. Baseline

      kubectl label --dry-run=server --overwrite ns --all \
      pod-security.kubernetes.io/enforce=baseline
      

      The output is similar to:

      namespace/default labeled
      namespace/kube-node-lease labeled
      namespace/kube-public labeled
      Warning: existing pods in namespace "kube-system" violate the new PodSecurity enforce level "baseline:latest"
      Warning: etcd-psa-wo-cluster-pss-control-plane (and 3 other pods): host namespaces, hostPath volumes
      Warning: kindnet-vzj42: non-default capabilities, host namespaces, hostPath volumes
      Warning: kube-proxy-m6hwf: host namespaces, hostPath volumes, privileged
      namespace/kube-system labeled
      namespace/local-path-storage labeled
      

   3. Restricted

      kubectl label --dry-run=server --overwrite ns --all \
      pod-security.kubernetes.io/enforce=restricted
      

      The output is similar to:

      namespace/default labeled
      namespace/kube-node-lease labeled
      namespace/kube-public labeled
      Warning: existing pods in namespace "kube-system" violate the new PodSecurity enforce level "restricted:latest"
      Warning: coredns-7bb9c7b568-hsptc (and 1 other pod): unrestricted capabilities, runAsNonRoot != true, seccompProfile
      Warning: etcd-psa-wo-cluster-pss-control-plane (and 3 other pods): host namespaces, hostPath volumes, allowPrivilegeEscalation != false, unrestricted capabilities, restricted volume types, runAsNonRoot != true
      Warning: kindnet-vzj42: non-default capabilities, host namespaces, hostPath volumes, allowPrivilegeEscalation != false, unrestricted capabilities, restricted volume types, runAsNonRoot != true, seccompProfile
      Warning: kube-proxy-m6hwf: host namespaces, hostPath volumes, privileged, allowPrivilegeEscalation != false, unrestricted capabilities, restricted volume types, runAsNonRoot != true, seccompProfile
      namespace/kube-system labeled
      Warning: existing pods in namespace "local-path-storage" violate the new PodSecurity enforce level "restricted:latest"
      Warning: local-path-provisioner-d6d9f7ffc-lw9lh: allowPrivilegeEscalation != false, unrestricted capabilities, runAsNonRoot != true, seccompProfile
      namespace/local-path-storage labeled
      

From the previous output, you'll notice that applying the privileged Pod Security Standard shows no warnings for any namespaces. However, baseline and restricted standards both have warnings, specifically in the kube-system namespace.

Set modes, versions and standards

In this section, you apply the following Pod Security Standards to the latest version:

• baseline standard in enforce mode.
• restricted standard in warn and audit mode.

The baseline Pod Security Standard provides a convenient middle ground that allows keeping the exemption list short and prevents known privilege escalations.

Additionally, to prevent pods from failing in kube-system, you'll exempt the namespace from having Pod Security Standards applied.

When you implement Pod Security Admission in your own environment, consider the following:

1. Based on the risk posture applied to a cluster, a stricter Pod Security Standard like restricted might be a better choice.

2. Exempting the kube-system namespace allows pods to run as privileged in this namespace. For real world use, the Kubernetes project strongly recommends that you apply strict RBAC policies that limit access to kube-system, following the principle of least privilege. To implement the preceding standards, do the following:

3. Create a configuration file that can be consumed by the Pod Security Admission Controller to implement these Pod Security Standards:

   mkdir -p /tmp/pss
   cat <<EOF > /tmp/pss/cluster-level-pss.yaml
   apiVersion: apiserver.config.k8s.io/v1
   kind: AdmissionConfiguration
   plugins:
   - name: PodSecurity
     configuration:
       apiVersion: pod-security.admission.config.k8s.io/v1
       kind: PodSecurityConfiguration
       defaults:
         enforce: "baseline"
         enforce-version: "latest"
         audit: "restricted"
         audit-version: "latest"
         warn: "restricted"
         warn-version: "latest"
       exemptions:
         usernames: []
         runtimeClasses: []
         namespaces: [kube-system]
   EOF
   

   Note: pod-security.admission.config.k8s.io/v1 configuration requires v1.25+. For v1.23 and v1.24, use v1beta1. For v1.22, use v1alpha1.

4. Configure the API server to consume this file during cluster creation:

   cat <<EOF > /tmp/pss/cluster-config.yaml
   kind: Cluster
   apiVersion: kind.x-k8s.io/v1alpha4
   nodes:
   - role: control-plane
     kubeadmConfigPatches:
     - |
       kind: ClusterConfiguration
       apiServer:
           extraArgs:
             admission-control-config-file: /etc/config/cluster-level-pss.yaml
           extraVolumes:
             - name: accf
               hostPath: /etc/config
               mountPath: /etc/config
               readOnly: false
               pathType: "DirectoryOrCreate"
     extraMounts:
     - hostPath: /tmp/pss
       containerPath: /etc/config
       # optional: if set, the mount is read-only.
       # default false
       readOnly: false
       # optional: if set, the mount needs SELinux relabeling.
       # default false
       selinuxRelabel: false
       # optional: set propagation mode (None, HostToContainer or Bidirectional)
       # see https://kubernetes.io/docs/concepts/storage/volumes/#mount-propagation
       # default None
       propagation: None
   EOF
   

   Note: If you use Docker Desktop with kind on macOS, you can add /tmp as a Shared Directory under the menu item Preferences > Resources > File Sharing.

5. Create a cluster that uses Pod Security Admission to apply these Pod Security Standards:

   kind create cluster --name psa-with-cluster-pss --config /tmp/pss/cluster-config.yaml
   

   The output is similar to this:

   Creating cluster "psa-with-cluster-pss" ...
    ✓ Ensuring node image (kindest/node:v1.29.2) 🖼
    ✓ Preparing nodes 📦
    ✓ Writing configuration 📜
    ✓ Starting control-plane 🕹️
    ✓ Installing CNI 🔌
    ✓ Installing StorageClass 💾
   Set kubectl context to "kind-psa-with-cluster-pss"
   You can now use your cluster with:
   
   kubectl cluster-info --context kind-psa-with-cluster-pss
   
   Have a question, bug, or feature request? Let us know! https://kind.sigs.k8s.io/#community 🙂
   

6. Point kubectl to the cluster:

   kubectl cluster-info --context kind-psa-with-cluster-pss
   

   The output is similar to this:

   Kubernetes control plane is running at https://127.0.0.1:63855
   CoreDNS is running at https://127.0.0.1:63855/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy
   
   To further debug and diagnose cluster problems, use 'kubectl cluster-info dump'.
   

7. Create a Pod in the default namespace:

   security/example-baseline-pod.yaml

   apiVersion: v1
    kind: Pod
    metadata:
      name: nginx
    spec:
      containers:
        - image: nginx
          name: nginx
          ports:
            - containerPort: 80
    

   kubectl apply -f https://k8s.io/examples/security/example-baseline-pod.yaml
   

   The pod is started normally, but the output includes a warning:

   Warning: would violate PodSecurity "restricted:latest": allowPrivilegeEscalation != false (container "nginx" must set securityContext.allowPrivilegeEscalation=false), unrestricted capabilities (container "nginx" must set securityContext.capabilities.drop=["ALL"]), runAsNonRoot != true (pod or container "nginx" must set securityContext.runAsNonRoot=true), seccompProfile (pod or container "nginx" must set securityContext.seccompProfile.type to "RuntimeDefault" or "Localhost")
   pod/nginx created
   

Clean up

Now delete the clusters which you created above by running the following command:

kind delete cluster --name psa-with-cluster-pss

kind delete cluster --name psa-wo-cluster-pss

What's next

• Run a shell script to perform all the preceding steps at once:
  1. Create a Pod Security Standards based cluster level Configuration
  2. Create a file to let API server consume this configuration
  3. Create a cluster that creates an API server with this configuration
  4. Set kubectl context to this new cluster
  5. Create a minimal pod yaml file
  6. Apply this file to create a Pod in the new cluster
• Pod Security Admission
• Pod Security Standards
• Apply Pod Security Standards at the namespace level

4.2 - Apply Pod Security Standards at the Namespace Level

Pod Security Admission is an admission controller that applies Pod Security Standards when pods are created. It is a feature GA'ed in v1.25. In this tutorial, you will enforce the baseline Pod Security Standard, one namespace at a time.

You can also apply Pod Security Standards to multiple namespaces at once at the cluster level. For instructions, refer to Apply Pod Security Standards at the cluster level.

Before you begin

Install the following on your workstation:

• kind
• kubectl

Create cluster

1. Create a kind cluster as follows:

   kind create cluster --name psa-ns-level
   

   The output is similar to this:

   Creating cluster "psa-ns-level" ...
    ✓ Ensuring node image (kindest/node:v1.29.2) 🖼 
    ✓ Preparing nodes 📦  
    ✓ Writing configuration 📜 
    ✓ Starting control-plane 🕹️ 
    ✓ Installing CNI 🔌 
    ✓ Installing StorageClass 💾 
   Set kubectl context to "kind-psa-ns-level"
   You can now use your cluster with:
   
   kubectl cluster-info --context kind-psa-ns-level
   
   Not sure what to do next? 😅  Check out https://kind.sigs.k8s.io/docs/user/quick-start/
   

2. Set the kubectl context to the new cluster:

   kubectl cluster-info --context kind-psa-ns-level
   

   The output is similar to this:

   Kubernetes control plane is running at https://127.0.0.1:50996
   CoreDNS is running at https://127.0.0.1:50996/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy
   
   To further debug and diagnose cluster problems, use 'kubectl cluster-info dump'.
   

Create a namespace

Create a new namespace called example:

kubectl create ns example

The output is similar to this:

namespace/example created

Enable Pod Security Standards checking for that namespace

1. Enable Pod Security Standards on this namespace using labels supported by built-in Pod Security Admission. In this step you will configure a check to warn on Pods that don't meet the latest version of the baseline pod security standard.

   kubectl label --overwrite ns example \
      pod-security.kubernetes.io/warn=baseline \
      pod-security.kubernetes.io/warn-version=latest
   

2. You can configure multiple pod security standard checks on any namespace, using labels. The following command will enforce the baseline Pod Security Standard, but warn and audit for restricted Pod Security Standards as per the latest version (default value)

   kubectl label --overwrite ns example \
     pod-security.kubernetes.io/enforce=baseline \
     pod-security.kubernetes.io/enforce-version=latest \
     pod-security.kubernetes.io/warn=restricted \
     pod-security.kubernetes.io/warn-version=latest \
     pod-security.kubernetes.io/audit=restricted \
     pod-security.kubernetes.io/audit-version=latest
   

Verify the Pod Security Standard enforcement

1. Create a baseline Pod in the example namespace:

   kubectl apply -n example -f https://k8s.io/examples/security/example-baseline-pod.yaml
   

   The Pod does start OK; the output includes a warning. For example:

   Warning: would violate PodSecurity "restricted:latest": allowPrivilegeEscalation != false (container "nginx" must set securityContext.allowPrivilegeEscalation=false), unrestricted capabilities (container "nginx" must set securityContext.capabilities.drop=["ALL"]), runAsNonRoot != true (pod or container "nginx" must set securityContext.runAsNonRoot=true), seccompProfile (pod or container "nginx" must set securityContext.seccompProfile.type to "RuntimeDefault" or "Localhost")
   pod/nginx created
   

2. Create a baseline Pod in the default namespace:

   kubectl apply -n default -f https://k8s.io/examples/security/example-baseline-pod.yaml
   

   Output is similar to this:

   pod/nginx created
   

The Pod Security Standards enforcement and warning settings were applied only to the example namespace. You could create the same Pod in the default namespace with no warnings.

Clean up

Now delete the cluster which you created above by running the following command:

kind delete cluster --name psa-ns-level

What's next

• Run a shell script to perform all the preceding steps all at once.

  1. Create kind cluster
  2. Create new namespace
  3. Apply baseline Pod Security Standard in enforce mode while applying restricted Pod Security Standard also in warn and audit mode.
  4. Create a new pod with the following pod security standards applied

• Pod Security Admission

• Pod Security Standards

• Apply Pod Security Standards at the cluster level

4.3 - Restrict a Container's Access to Resources with AppArmor

AppArmor is a Linux kernel security module that supplements the standard Linux user and group based permissions to confine programs to a limited set of resources. AppArmor can be configured for any application to reduce its potential attack surface and provide greater in-depth defense. It is configured through profiles tuned to allow the access needed by a specific program or container, such as Linux capabilities, network access, file permissions, etc. Each profile can be run in either enforcing mode, which blocks access to disallowed resources, or complain mode, which only reports violations.

AppArmor can help you to run a more secure deployment by restricting what containers are allowed to do, and/or provide better auditing through system logs. However, it is important to keep in mind that AppArmor is not a silver bullet and can only do so much to protect against exploits in your application code. It is important to provide good, restrictive profiles, and harden your applications and cluster from other angles as well.

Objectives

• See an example of how to load a profile on a node
• Learn how to enforce the profile on a Pod
• Learn how to check that the profile is loaded
• See what happens when a profile is violated
• See what happens when a profile cannot be loaded

Before you begin

Make sure:

1. Kubernetes version is at least v1.4 -- Kubernetes support for AppArmor was added in v1.4. Kubernetes components older than v1.4 are not aware of the new AppArmor annotations, and will silently ignore any AppArmor settings that are provided. To ensure that your Pods are receiving the expected protections, it is important to verify the Kubelet version of your nodes:

   kubectl get nodes -o=jsonpath=$'{range .items[*]}{@.metadata.name}: {@.status.nodeInfo.kubeletVersion}\n{end}'
   

   gke-test-default-pool-239f5d02-gyn2: v1.4.0
   gke-test-default-pool-239f5d02-x1kf: v1.4.0
   gke-test-default-pool-239f5d02-xwux: v1.4.0
   

2. AppArmor kernel module is enabled -- For the Linux kernel to enforce an AppArmor profile, the AppArmor kernel module must be installed and enabled. Several distributions enable the module by default, such as Ubuntu and SUSE, and many others provide optional support. To check whether the module is enabled, check the /sys/module/apparmor/parameters/enabled file:

   cat /sys/module/apparmor/parameters/enabled
   Y
   

   If the Kubelet contains AppArmor support (>= v1.4), it will refuse to run a Pod with AppArmor options if the kernel module is not enabled.

3. Container runtime supports AppArmor -- Currently all common Kubernetes-supported container runtimes should support AppArmor, like Docker, CRI-O or containerd. Please refer to the corresponding runtime documentation and verify that the cluster fulfills the requirements to use AppArmor.

4. Profile is loaded -- AppArmor is applied to a Pod by specifying an AppArmor profile that each container should be run with. If any of the specified profiles is not already loaded in the kernel, the Kubelet (>= v1.4) will reject the Pod. You can view which profiles are loaded on a node by checking the /sys/kernel/security/apparmor/profiles file. For example:

   ssh gke-test-default-pool-239f5d02-gyn2 "sudo cat /sys/kernel/security/apparmor/profiles | sort"
   

   apparmor-test-deny-write (enforce)
   apparmor-test-audit-write (enforce)
   docker-default (enforce)
   k8s-nginx (enforce)
   

   For more details on loading profiles on nodes, see Setting up nodes with profiles.

As long as the Kubelet version includes AppArmor support (>= v1.4), the Kubelet will reject a Pod with AppArmor options if any of the prerequisites are not met. You can also verify AppArmor support on nodes by checking the node ready condition message (though this is likely to be removed in a later release):

kubectl get nodes -o=jsonpath='{range .items[*]}{@.metadata.name}: {.status.conditions[?(@.reason=="KubeletReady")].message}{"\n"}{end}'

gke-test-default-pool-239f5d02-gyn2: kubelet is posting ready status. AppArmor enabled
gke-test-default-pool-239f5d02-x1kf: kubelet is posting ready status. AppArmor enabled
gke-test-default-pool-239f5d02-xwux: kubelet is posting ready status. AppArmor enabled

Securing a Pod

AppArmor profiles are specified per-container. To specify the AppArmor profile to run a Pod container with, add an annotation to the Pod's metadata:

container.apparmor.security.beta.kubernetes.io/<container_name>: <profile_ref>

Where <container_name> is the name of the container to apply the profile to, and <profile_ref> specifies the profile to apply. The profile_ref can be one of:

• runtime/default to apply the runtime's default profile
• localhost/<profile_name> to apply the profile loaded on the host with the name <profile_name>
• unconfined to indicate that no profiles will be loaded

See the API Reference for the full details on the annotation and profile name formats.

Kubernetes AppArmor enforcement works by first checking that all the prerequisites have been met, and then forwarding the profile selection to the container runtime for enforcement. If the prerequisites have not been met, the Pod will be rejected, and will not run.

To verify that the profile was applied, you can look for the AppArmor security option listed in the container created event:

kubectl get events | grep Created

22s        22s         1         hello-apparmor     Pod       spec.containers{hello}   Normal    Created     {kubelet e2e-test-stclair-node-pool-31nt}   Created container with docker id 269a53b202d3; Security:[seccomp=unconfined apparmor=k8s-apparmor-example-deny-write]

You can also verify directly that the container's root process is running with the correct profile by checking its proc attr:

kubectl exec <pod_name> -- cat /proc/1/attr/current

k8s-apparmor-example-deny-write (enforce)

Example

This example assumes you have already set up a cluster with AppArmor support.

First, we need to load the profile we want to use onto our nodes. This profile denies all file writes:

#include <tunables/global>

profile k8s-apparmor-example-deny-write flags=(attach_disconnected) {
  #include <abstractions/base>

  file,

  # Deny all file writes.
  deny /** w,
}

Since we don't know where the Pod will be scheduled, we'll need to load the profile on all our nodes. For this example we'll use SSH to install the profiles, but other approaches are discussed in Setting up nodes with profiles.

NODES=(
    # The SSH-accessible domain names of your nodes
    gke-test-default-pool-239f5d02-gyn2.us-central1-a.my-k8s
    gke-test-default-pool-239f5d02-x1kf.us-central1-a.my-k8s
    gke-test-default-pool-239f5d02-xwux.us-central1-a.my-k8s)
for NODE in ${NODES[*]}; do ssh $NODE 'sudo apparmor_parser -q <<EOF
#include <tunables/global>

profile k8s-apparmor-example-deny-write flags=(attach_disconnected) {
  #include <abstractions/base>

  file,

  # Deny all file writes.
  deny /** w,
}
EOF'
done

Next, we'll run a simple "Hello AppArmor" pod with the deny-write profile:

pods/security/hello-apparmor.yaml

apiVersion: v1
kind: Pod
metadata:
  name: hello-apparmor
  annotations:
    # Tell Kubernetes to apply the AppArmor profile "k8s-apparmor-example-deny-write".
    # Note that this is ignored if the Kubernetes node is not running version 1.4 or greater.
    container.apparmor.security.beta.kubernetes.io/hello: localhost/k8s-apparmor-example-deny-write
spec:
  containers:
  - name: hello
    image: busybox:1.28
    command: [ "sh", "-c", "echo 'Hello AppArmor!' && sleep 1h" ]

kubectl create -f ./hello-apparmor.yaml

If we look at the pod events, we can see that the Pod container was created with the AppArmor profile "k8s-apparmor-example-deny-write":

kubectl get events | grep hello-apparmor

14s        14s         1         hello-apparmor   Pod                                Normal    Scheduled   {default-scheduler }                           Successfully assigned hello-apparmor to gke-test-default-pool-239f5d02-gyn2
14s        14s         1         hello-apparmor   Pod       spec.containers{hello}   Normal    Pulling     {kubelet gke-test-default-pool-239f5d02-gyn2}   pulling image "busybox"
13s        13s         1         hello-apparmor   Pod       spec.containers{hello}   Normal    Pulled      {kubelet gke-test-default-pool-239f5d02-gyn2}   Successfully pulled image "busybox"
13s        13s         1         hello-apparmor   Pod       spec.containers{hello}   Normal    Created     {kubelet gke-test-default-pool-239f5d02-gyn2}   Created container with docker id 06b6cd1c0989; Security:[seccomp=unconfined apparmor=k8s-apparmor-example-deny-write]
13s        13s         1         hello-apparmor   Pod       spec.containers{hello}   Normal    Started     {kubelet gke-test-default-pool-239f5d02-gyn2}   Started container with docker id 06b6cd1c0989

We can verify that the container is actually running with that profile by checking its proc attr:

kubectl exec hello-apparmor -- cat /proc/1/attr/current

k8s-apparmor-example-deny-write (enforce)

Finally, we can see what happens if we try to violate the profile by writing to a file:

kubectl exec hello-apparmor -- touch /tmp/test

touch: /tmp/test: Permission denied
error: error executing remote command: command terminated with non-zero exit code: Error executing in Docker Container: 1

To wrap up, let's look at what happens if we try to specify a profile that hasn't been loaded:

kubectl create -f /dev/stdin <<EOF

apiVersion: v1
kind: Pod
metadata:
  name: hello-apparmor-2
  annotations:
    container.apparmor.security.beta.kubernetes.io/hello: localhost/k8s-apparmor-example-allow-write
spec:
  containers:
  - name: hello
    image: busybox:1.28
    command: [ "sh", "-c", "echo 'Hello AppArmor!' && sleep 1h" ]
EOF
pod/hello-apparmor-2 created

kubectl describe pod hello-apparmor-2

Name:          hello-apparmor-2
Namespace:     default
Node:          gke-test-default-pool-239f5d02-x1kf/
Start Time:    Tue, 30 Aug 2016 17:58:56 -0700
Labels:        <none>
Annotations:   container.apparmor.security.beta.kubernetes.io/hello=localhost/k8s-apparmor-example-allow-write
Status:        Pending
Reason:        AppArmor
Message:       Pod Cannot enforce AppArmor: profile "k8s-apparmor-example-allow-write" is not loaded
IP:
Controllers:   <none>
Containers:
  hello:
    Container ID:
    Image:     busybox
    Image ID:
    Port:
    Command:
      sh
      -c
      echo 'Hello AppArmor!' && sleep 1h
    State:              Waiting
      Reason:           Blocked
    Ready:              False
    Restart Count:      0
    Environment:        <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-dnz7v (ro)
Conditions:
  Type          Status
  Initialized   True
  Ready         False
  PodScheduled  True
Volumes:
  default-token-dnz7v:
    Type:    Secret (a volume populated by a Secret)
    SecretName:    default-token-dnz7v
    Optional:   false
QoS Class:      BestEffort
Node-Selectors: <none>
Tolerations:    <none>
Events:
  FirstSeen    LastSeen    Count    From                        SubobjectPath    Type        Reason        Message
  ---------    --------    -----    ----                        -------------    --------    ------        -------
  23s          23s         1        {default-scheduler }                         Normal      Scheduled     Successfully assigned hello-apparmor-2 to e2e-test-stclair-node-pool-t1f5
  23s          23s         1        {kubelet e2e-test-stclair-node-pool-t1f5}             Warning        AppArmor    Cannot enforce AppArmor: profile "k8s-apparmor-example-allow-write" is not loaded

Note the pod status is Pending, with a helpful error message: Pod Cannot enforce AppArmor: profile "k8s-apparmor-example-allow-write" is not loaded. An event was also recorded with the same message.

Administration

Setting up nodes with profiles

Kubernetes does not currently provide any native mechanisms for loading AppArmor profiles onto nodes. There are lots of ways to set up the profiles though, such as:

• Through a DaemonSet that runs a Pod on each node to ensure the correct profiles are loaded. An example implementation can be found here.
• At node initialization time, using your node initialization scripts (e.g. Salt, Ansible, etc.) or image.
• By copying the profiles to each node and loading them through SSH, as demonstrated in the Example.

The scheduler is not aware of which profiles are loaded onto which node, so the full set of profiles must be loaded onto every node. An alternative approach is to add a node label for each profile (or class of profiles) on the node, and use a node selector to ensure the Pod is run on a node with the required profile.

Disabling AppArmor

If you do not want AppArmor to be available on your cluster, it can be disabled by a command-line flag:

--feature-gates=AppArmor=false

When disabled, any Pod that includes an AppArmor profile will fail validation with a "Forbidden" error.

Authoring Profiles

Getting AppArmor profiles specified correctly can be a tricky business. Fortunately there are some tools to help with that:

• aa-genprof and aa-logprof generate profile rules by monitoring an application's activity and logs, and admitting the actions it takes. Further instructions are provided by the AppArmor documentation.
• bane is an AppArmor profile generator for Docker that uses a simplified profile language.

To debug problems with AppArmor, you can check the system logs to see what, specifically, was denied. AppArmor logs verbose messages to dmesg, and errors can usually be found in the system logs or through journalctl. More information is provided in AppArmor failures.

API Reference

Pod Annotation

Specifying the profile a container will run with:

• key: container.apparmor.security.beta.kubernetes.io/<container_name> Where <container_name> matches the name of a container in the Pod. A separate profile can be specified for each container in the Pod.
• value: a profile reference, described below

Profile Reference

• runtime/default: Refers to the default runtime profile.
  • Equivalent to not specifying a profile, except it still requires AppArmor to be enabled.
  • In practice, many container runtimes use the same OCI default profile, defined here: https://github.com/containers/common/blob/main/pkg/apparmor/apparmor_linux_template.go
• localhost/<profile_name>: Refers to a profile loaded on the node (localhost) by name.
  • The possible profile names are detailed in the core policy reference.
• unconfined: This effectively disables AppArmor on the container.

Any other profile reference format is invalid.

What's next

Additional resources:

• Quick guide to the AppArmor profile language
• AppArmor core policy reference

4.4 - Restrict a Container's Syscalls with seccomp

Seccomp stands for secure computing mode and has been a feature of the Linux kernel since version 2.6.12. It can be used to sandbox the privileges of a process, restricting the calls it is able to make from userspace into the kernel. Kubernetes lets you automatically apply seccomp profiles loaded onto a node to your Pods and containers.

Identifying the privileges required for your workloads can be difficult. In this tutorial, you will go through how to load seccomp profiles into a local Kubernetes cluster, how to apply them to a Pod, and how you can begin to craft profiles that give only the necessary privileges to your container processes.

Objectives

• Learn how to load seccomp profiles on a node
• Learn how to apply a seccomp profile to a container
• Observe auditing of syscalls made by a container process
• Observe behavior when a missing profile is specified
• Observe a violation of a seccomp profile
• Learn how to create fine-grained seccomp profiles
• Learn how to apply a container runtime default seccomp profile

Before you begin

In order to complete all steps in this tutorial, you must install kind and kubectl.

The commands used in the tutorial assume that you are using Docker as your container runtime. (The cluster that kind creates may use a different container runtime internally). You could also use Podman but in that case, you would have to follow specific instructions in order to complete the tasks successfully.

This tutorial shows some examples that are still beta (since v1.25) and others that use only generally available seccomp functionality. You should make sure that your cluster is configured correctly for the version you are using.

The tutorial also uses the curl tool for downloading examples to your computer. You can adapt the steps to use a different tool if you prefer.

Download example seccomp profiles

The contents of these profiles will be explored later on, but for now go ahead and download them into a directory named profiles/ so that they can be loaded into the cluster.

• audit.json
• violation.json
• fine-grained.json

pods/security/seccomp/profiles/audit.json

{
    "defaultAction": "SCMP_ACT_LOG"
}

pods/security/seccomp/profiles/violation.json

{
    "defaultAction": "SCMP_ACT_ERRNO"
}

pods/security/seccomp/profiles/fine-grained.json

{
    "defaultAction": "SCMP_ACT_ERRNO",
    "architectures": [
        "SCMP_ARCH_X86_64",
        "SCMP_ARCH_X86",
        "SCMP_ARCH_X32"
    ],
    "syscalls": [
        {
            "names": [
                "accept4",
                "epoll_wait",
                "pselect6",
                "futex",
                "madvise",
                "epoll_ctl",
                "getsockname",
                "setsockopt",
                "vfork",
                "mmap",
                "read",
                "write",
                "close",
                "arch_prctl",
                "sched_getaffinity",
                "munmap",
                "brk",
                "rt_sigaction",
                "rt_sigprocmask",
                "sigaltstack",
                "gettid",
                "clone",
                "bind",
                "socket",
                "openat",
                "readlinkat",
                "exit_group",
                "epoll_create1",
                "listen",
                "rt_sigreturn",
                "sched_yield",
                "clock_gettime",
                "connect",
                "dup2",
                "epoll_pwait",
                "execve",
                "exit",
                "fcntl",
                "getpid",
                "getuid",
                "ioctl",
                "mprotect",
                "nanosleep",
                "open",
                "poll",
                "recvfrom",
                "sendto",
                "set_tid_address",
                "setitimer",
                "writev"
            ],
            "action": "SCMP_ACT_ALLOW"
        }
    ]
}

Run these commands:

mkdir ./profiles
curl -L -o profiles/audit.json https://k8s.io/examples/pods/security/seccomp/profiles/audit.json
curl -L -o profiles/violation.json https://k8s.io/examples/pods/security/seccomp/profiles/violation.json
curl -L -o profiles/fine-grained.json https://k8s.io/examples/pods/security/seccomp/profiles/fine-grained.json
ls profiles

You should see three profiles listed at the end of the final step:

audit.json  fine-grained.json  violation.json

Create a local Kubernetes cluster with kind

For simplicity, kind can be used to create a single node cluster with the seccomp profiles loaded. Kind runs Kubernetes in Docker, so each node of the cluster is a container. This allows for files to be mounted in the filesystem of each container similar to loading files onto a node.

pods/security/seccomp/kind.yaml

apiVersion: kind.x-k8s.io/v1alpha4
kind: Cluster
nodes:
- role: control-plane
  extraMounts:
  - hostPath: "./profiles"
    containerPath: "/var/lib/kubelet/seccomp/profiles"

Download that example kind configuration, and save it to a file named kind.yaml:

curl -L -O https://k8s.io/examples/pods/security/seccomp/kind.yaml

You can set a specific Kubernetes version by setting the node's container image. See Nodes within the kind documentation about configuration for more details on this. This tutorial assumes you are using Kubernetes v1.29.

As a beta feature, you can configure Kubernetes to use the profile that the container runtime prefers by default, rather than falling back to Unconfined. If you want to try that, see enable the use of RuntimeDefault as the default seccomp profile for all workloads before you continue.

Once you have a kind configuration in place, create the kind cluster with that configuration:

kind create cluster --config=kind.yaml

After the new Kubernetes cluster is ready, identify the Docker container running as the single node cluster:

docker ps

You should see output indicating that a container is running with name kind-control-plane. The output is similar to:

CONTAINER ID        IMAGE                  COMMAND                  CREATED             STATUS              PORTS                       NAMES
6a96207fed4b        kindest/node:v1.18.2   "/usr/local/bin/entr…"   27 seconds ago      Up 24 seconds       127.0.0.1:42223->6443/tcp   kind-control-plane

If observing the filesystem of that container, you should see that the profiles/ directory has been successfully loaded into the default seccomp path of the kubelet. Use docker exec to run a command in the Pod:

# Change 6a96207fed4b to the container ID you saw from "docker ps"
docker exec -it 6a96207fed4b ls /var/lib/kubelet/seccomp/profiles

audit.json  fine-grained.json  violation.json

You have verified that these seccomp profiles are available to the kubelet running within kind.

Create a Pod that uses the container runtime default seccomp profile

Most container runtimes provide a sane set of default syscalls that are allowed or not. You can adopt these defaults for your workload by setting the seccomp type in the security context of a pod or container to RuntimeDefault.

Here's a manifest for a Pod that requests the RuntimeDefault seccomp profile for all its containers:

pods/security/seccomp/ga/default-pod.yaml

apiVersion: v1
kind: Pod
metadata:
  name: default-pod
  labels:
    app: default-pod
spec:
  securityContext:
    seccompProfile:
      type: RuntimeDefault
  containers:
  - name: test-container
    image: hashicorp/http-echo:1.0
    args:
    - "-text=just made some more syscalls!"
    securityContext:
      allowPrivilegeEscalation: false

Create that Pod:

kubectl apply -f https://k8s.io/examples/pods/security/seccomp/ga/default-pod.yaml

kubectl get pod default-pod

The Pod should be showing as having started successfully:

NAME        READY   STATUS    RESTARTS   AGE
default-pod 1/1     Running   0          20s

Delete the Pod before moving to the next section:

kubectl delete pod default-pod --wait --now

Create a Pod with a seccomp profile for syscall auditing

To start off, apply the audit.json profile, which will log all syscalls of the process, to a new Pod.

Here's a manifest for that Pod:

pods/security/seccomp/ga/audit-pod.yaml

apiVersion: v1
kind: Pod
metadata:
  name: audit-pod
  labels:
    app: audit-pod
spec:
  securityContext:
    seccompProfile:
      type: Localhost
      localhostProfile: profiles/audit.json
  containers:
  - name: test-container
    image: hashicorp/http-echo:1.0
    args:
    - "-text=just made some syscalls!"
    securityContext:
      allowPrivilegeEscalation: false

Create the Pod in the cluster:

kubectl apply -f https://k8s.io/examples/pods/security/seccomp/ga/audit-pod.yaml

This profile does not restrict any syscalls, so the Pod should start successfully.

kubectl get pod audit-pod

NAME        READY   STATUS    RESTARTS   AGE
audit-pod   1/1     Running   0          30s

In order to be able to interact with this endpoint exposed by this container, create a NodePort Service that allows access to the endpoint from inside the kind control plane container.

kubectl expose pod audit-pod --type NodePort --port 5678

Check what port the Service has been assigned on the node.

kubectl get service audit-pod

The output is similar to:

NAME        TYPE       CLUSTER-IP      EXTERNAL-IP   PORT(S)          AGE
audit-pod   NodePort   10.111.36.142   <none>        5678:32373/TCP   72s

Now you can use curl to access that endpoint from inside the kind control plane container, at the port exposed by this Service. Use docker exec to run the curl command within the container belonging to that control plane container:

# Change 6a96207fed4b to the control plane container ID and 32373 to the port number you saw from "docker ps"
docker exec -it 6a96207fed4b curl localhost:32373

just made some syscalls!

You can see that the process is running, but what syscalls did it actually make? Because this Pod is running in a local cluster, you should be able to see those in /var/log/syslog on your local system. Open up a new terminal window and tail the output for calls from http-echo:

# The log path on your computer might be different from "/var/log/syslog"
tail -f /var/log/syslog | grep 'http-echo'

You should already see some logs of syscalls made by http-echo, and if you run curl again inside the control plane container you will see more output written to the log.

For example:

Jul  6 15:37:40 my-machine kernel: [369128.669452] audit: type=1326 audit(1594067860.484:14536): auid=4294967295 uid=0 gid=0 ses=4294967295 pid=29064 comm="http-echo" exe="/http-echo" sig=0 arch=c000003e syscall=51 compat=0 ip=0x46fe1f code=0x7ffc0000
Jul  6 15:37:40 my-machine kernel: [369128.669453] audit: type=1326 audit(1594067860.484:14537): auid=4294967295 uid=0 gid=0 ses=4294967295 pid=29064 comm="http-echo" exe="/http-echo" sig=0 arch=c000003e syscall=54 compat=0 ip=0x46fdba code=0x7ffc0000
Jul  6 15:37:40 my-machine kernel: [369128.669455] audit: type=1326 audit(1594067860.484:14538): auid=4294967295 uid=0 gid=0 ses=4294967295 pid=29064 comm="http-echo" exe="/http-echo" sig=0 arch=c000003e syscall=202 compat=0 ip=0x455e53 code=0x7ffc0000
Jul  6 15:37:40 my-machine kernel: [369128.669456] audit: type=1326 audit(1594067860.484:14539): auid=4294967295 uid=0 gid=0 ses=4294967295 pid=29064 comm="http-echo" exe="/http-echo" sig=0 arch=c000003e syscall=288 compat=0 ip=0x46fdba code=0x7ffc0000
Jul  6 15:37:40 my-machine kernel: [369128.669517] audit: type=1326 audit(1594067860.484:14540): auid=4294967295 uid=0 gid=0 ses=4294967295 pid=29064 comm="http-echo" exe="/http-echo" sig=0 arch=c000003e syscall=0 compat=0 ip=0x46fd44 code=0x7ffc0000
Jul  6 15:37:40 my-machine kernel: [369128.669519] audit: type=1326 audit(1594067860.484:14541): auid=4294967295 uid=0 gid=0 ses=4294967295 pid=29064 comm="http-echo" exe="/http-echo" sig=0 arch=c000003e syscall=270 compat=0 ip=0x4559b1 code=0x7ffc0000
Jul  6 15:38:40 my-machine kernel: [369188.671648] audit: type=1326 audit(1594067920.488:14559): auid=4294967295 uid=0 gid=0 ses=4294967295 pid=29064 comm="http-echo" exe="/http-echo" sig=0 arch=c000003e syscall=270 compat=0 ip=0x4559b1 code=0x7ffc0000
Jul  6 15:38:40 my-machine kernel: [369188.671726] audit: type=1326 audit(1594067920.488:14560): auid=4294967295 uid=0 gid=0 ses=4294967295 pid=29064 comm="http-echo" exe="/http-echo" sig=0 arch=c000003e syscall=202 compat=0 ip=0x455e53 code=0x7ffc0000

You can begin to understand the syscalls required by the http-echo process by looking at the syscall= entry on each line. While these are unlikely to encompass all syscalls it uses, it can serve as a basis for a seccomp profile for this container.

Delete the Service and the Pod before moving to the next section:

kubectl delete service audit-pod --wait
kubectl delete pod audit-pod --wait --now

Create a Pod with a seccomp profile that causes violation

For demonstration, apply a profile to the Pod that does not allow for any syscalls.

The manifest for this demonstration is:

pods/security/seccomp/ga/violation-pod.yaml

apiVersion: v1
kind: Pod
metadata:
  name: violation-pod
  labels:
    app: violation-pod
spec:
  securityContext:
    seccompProfile:
      type: Localhost
      localhostProfile: profiles/violation.json
  containers:
  - name: test-container
    image: hashicorp/http-echo:1.0
    args:
    - "-text=just made some syscalls!"
    securityContext:
      allowPrivilegeEscalation: false

Attempt to create the Pod in the cluster:

kubectl apply -f https://k8s.io/examples/pods/security/seccomp/ga/violation-pod.yaml

The Pod creates, but there is an issue. If you check the status of the Pod, you should see that it failed to start.

kubectl get pod violation-pod

NAME            READY   STATUS             RESTARTS   AGE
violation-pod   0/1     CrashLoopBackOff   1          6s

As seen in the previous example, the http-echo process requires quite a few syscalls. Here seccomp has been instructed to error on any syscall by setting "defaultAction": "SCMP_ACT_ERRNO". This is extremely secure, but removes the ability to do anything meaningful. What you really want is to give workloads only the privileges they need.

Delete the Pod before moving to the next section:

kubectl delete pod violation-pod --wait --now

Create a Pod with a seccomp profile that only allows necessary syscalls

If you take a look at the fine-grained.json profile, you will notice some of the syscalls seen in syslog of the first example where the profile set "defaultAction": "SCMP_ACT_LOG". Now the profile is setting "defaultAction": "SCMP_ACT_ERRNO", but explicitly allowing a set of syscalls in the "action": "SCMP_ACT_ALLOW" block. Ideally, the container will run successfully and you will see no messages sent to syslog.

The manifest for this example is:

pods/security/seccomp/ga/fine-pod.yaml

apiVersion: v1
kind: Pod
metadata:
  name: fine-pod
  labels:
    app: fine-pod
spec:
  securityContext:
    seccompProfile:
      type: Localhost
      localhostProfile: profiles/fine-grained.json
  containers:
  - name: test-container
    image: hashicorp/http-echo:1.0
    args:
    - "-text=just made some syscalls!"
    securityContext:
      allowPrivilegeEscalation: false

Create the Pod in your cluster:

kubectl apply -f https://k8s.io/examples/pods/security/seccomp/ga/fine-pod.yaml

kubectl get pod fine-pod

The Pod should be showing as having started successfully:

NAME        READY   STATUS    RESTARTS   AGE
fine-pod   1/1     Running   0          30s

Open up a new terminal window and use tail to monitor for log entries that mention calls from http-echo:

# The log path on your computer might be different from "/var/log/syslog"
tail -f /var/log/syslog | grep 'http-echo'

Next, expose the Pod with a NodePort Service:

kubectl expose pod fine-pod --type NodePort --port 5678

Check what port the Service has been assigned on the node:

kubectl get service fine-pod

The output is similar to:

NAME        TYPE       CLUSTER-IP      EXTERNAL-IP   PORT(S)          AGE
fine-pod    NodePort   10.111.36.142   <none>        5678:32373/TCP   72s

Use curl to access that endpoint from inside the kind control plane container:

# Change 6a96207fed4b to the control plane container ID and 32373 to the port number you saw from "docker ps"
docker exec -it 6a96207fed4b curl localhost:32373

just made some syscalls!

You should see no output in the syslog. This is because the profile allowed all necessary syscalls and specified that an error should occur if one outside of the list is invoked. This is an ideal situation from a security perspective, but required some effort in analyzing the program. It would be nice if there was a simple way to get closer to this security without requiring as much effort.

Delete the Service and the Pod before moving to the next section:

kubectl delete service fine-pod --wait
kubectl delete pod fine-pod --wait --now

Enable the use of RuntimeDefault as the default seccomp profile for all workloads

To use seccomp profile defaulting, you must run the kubelet with the --seccomp-default command line flag enabled for each node where you want to use it.

If enabled, the kubelet will use the RuntimeDefault seccomp profile by default, which is defined by the container runtime, instead of using the Unconfined (seccomp disabled) mode. The default profiles aim to provide a strong set of security defaults while preserving the functionality of the workload. It is possible that the default profiles differ between container runtimes and their release versions, for example when comparing those from CRI-O and containerd.

Some workloads may require a lower amount of syscall restrictions than others. This means that they can fail during runtime even with the RuntimeDefault profile. To mitigate such a failure, you can:

• Run the workload explicitly as Unconfined.
• Disable the SeccompDefault feature for the nodes. Also making sure that workloads get scheduled on nodes where the feature is disabled.
• Create a custom seccomp profile for the workload.

If you were introducing this feature into production-like cluster, the Kubernetes project recommends that you enable this feature gate on a subset of your nodes and then test workload execution before rolling the change out cluster-wide.

You can find more detailed information about a possible upgrade and downgrade strategy in the related Kubernetes Enhancement Proposal (KEP): Enable seccomp by default.

Kubernetes 1.29 lets you configure the seccomp profile that applies when the spec for a Pod doesn't define a specific seccomp profile. However, you still need to enable this defaulting for each node where you would like to use it.

If you are running a Kubernetes 1.29 cluster and want to enable the feature, either run the kubelet with the --seccomp-default command line flag, or enable it through the kubelet configuration file. To enable the feature gate in kind, ensure that kind provides the minimum required Kubernetes version and enables the SeccompDefault feature in the kind configuration:

kind: Cluster
apiVersion: kind.x-k8s.io/v1alpha4
nodes:
  - role: control-plane
    image: kindest/node:v1.28.0@sha256:9f3ff58f19dcf1a0611d11e8ac989fdb30a28f40f236f59f0bea31fb956ccf5c
    kubeadmConfigPatches:
      - |
        kind: JoinConfiguration
        nodeRegistration:
          kubeletExtraArgs:
            seccomp-default: "true"        
  - role: worker
    image: kindest/node:v1.28.0@sha256:9f3ff58f19dcf1a0611d11e8ac989fdb30a28f40f236f59f0bea31fb956ccf5c
    kubeadmConfigPatches:
      - |
        kind: JoinConfiguration
        nodeRegistration:
          kubeletExtraArgs:
            seccomp-default: "true"        

If the cluster is ready, then running a pod:

kubectl run --rm -it --restart=Never --image=alpine alpine -- sh

Should now have the default seccomp profile attached. This can be verified by using docker exec to run crictl inspect for the container on the kind worker:

docker exec -it kind-worker bash -c \
    'crictl inspect $(crictl ps --name=alpine -q) | jq .info.runtimeSpec.linux.seccomp'

{
  "defaultAction": "SCMP_ACT_ERRNO",
  "architectures": ["SCMP_ARCH_X86_64", "SCMP_ARCH_X86", "SCMP_ARCH_X32"],
  "syscalls": [
    {
      "names": ["..."]
    }
  ]
}

What's next

You can learn more about Linux seccomp:

• A seccomp Overview
• Seccomp Security Profiles for Docker

5 - Stateless Applications

5.1 - Exposing an External IP Address to Access an Application in a Cluster

This page shows how to create a Kubernetes Service object that exposes an external IP address.

Before you begin

• Install kubectl.
• Use a cloud provider like Google Kubernetes Engine or Amazon Web Services to create a Kubernetes cluster. This tutorial creates an external load balancer, which requires a cloud provider.
• Configure kubectl to communicate with your Kubernetes API server. For instructions, see the documentation for your cloud provider.

Objectives

• Run five instances of a Hello World application.
• Create a Service object that exposes an external IP address.
• Use the Service object to access the running application.

Creating a service for an application running in five pods

1. Run a Hello World application in your cluster:

   service/load-balancer-example.yaml

   apiVersion: apps/v1
   kind: Deployment
   metadata:
     labels:
       app.kubernetes.io/name: load-balancer-example
     name: hello-world
   spec:
     replicas: 5
     selector:
       matchLabels:
         app.kubernetes.io/name: load-balancer-example
     template:
       metadata:
         labels:
           app.kubernetes.io/name: load-balancer-example
       spec:
         containers:
         - image: gcr.io/google-samples/node-hello:1.0
           name: hello-world
           ports:
           - containerPort: 8080
   

   kubectl apply -f https://k8s.io/examples/service/load-balancer-example.yaml
   

   The preceding command creates a Deployment and an associated ReplicaSet. The ReplicaSet has five Pods each of which runs the Hello World application.

2. Display information about the Deployment:

   kubectl get deployments hello-world
   kubectl describe deployments hello-world
   

3. Display information about your ReplicaSet objects:

   kubectl get replicasets
   kubectl describe replicasets
   

4. Create a Service object that exposes the deployment:

   kubectl expose deployment hello-world --type=LoadBalancer --name=my-service
   

5. Display information about the Service:

   kubectl get services my-service
   

   The output is similar to:

   NAME         TYPE           CLUSTER-IP     EXTERNAL-IP      PORT(S)    AGE
   my-service   LoadBalancer   10.3.245.137   104.198.205.71   8080/TCP   54s
   

   Note: The type=LoadBalancer service is backed by external cloud providers, which is not covered in this example, please refer to this page for the details.
   Note: If the external IP address is shown as <pending>, wait for a minute and enter the same command again.

6. Display detailed information about the Service:

   kubectl describe services my-service
   

   The output is similar to:

   Name:           my-service
   Namespace:      default
   Labels:         app.kubernetes.io/name=load-balancer-example
   Annotations:    <none>
   Selector:       app.kubernetes.io/name=load-balancer-example
   Type:           LoadBalancer
   IP:             10.3.245.137
   LoadBalancer Ingress:   104.198.205.71
   Port:           <unset> 8080/TCP
   NodePort:       <unset> 32377/TCP
   Endpoints:      10.0.0.6:8080,10.0.1.6:8080,10.0.1.7:8080 + 2 more...
   Session Affinity:   None
   Events:         <none>
   

   Make a note of the external IP address (LoadBalancer Ingress) exposed by your service. In this example, the external IP address is 104.198.205.71. Also note the value of Port and NodePort. In this example, the Port is 8080 and the NodePort is 32377.

7. In the preceding output, you can see that the service has several endpoints: 10.0.0.6:8080,10.0.1.6:8080,10.0.1.7:8080 + 2 more. These are internal addresses of the pods that are running the Hello World application. To verify these are pod addresses, enter this command:

   kubectl get pods --output=wide
   

   The output is similar to:

   NAME                         ...  IP         NODE
   hello-world-2895499144-1jaz9 ...  10.0.1.6   gke-cluster-1-default-pool-e0b8d269-1afc
   hello-world-2895499144-2e5uh ...  10.0.1.8   gke-cluster-1-default-pool-e0b8d269-1afc
   hello-world-2895499144-9m4h1 ...  10.0.0.6   gke-cluster-1-default-pool-e0b8d269-5v7a
   hello-world-2895499144-o4z13 ...  10.0.1.7   gke-cluster-1-default-pool-e0b8d269-1afc
   hello-world-2895499144-segjf ...  10.0.2.5   gke-cluster-1-default-pool-e0b8d269-cpuc
   

8. Use the external IP address (LoadBalancer Ingress) to access the Hello World application:

   curl http://<external-ip>:<port>
   

   where <external-ip> is the external IP address (LoadBalancer Ingress) of your Service, and <port> is the value of Port in your Service description. If you are using minikube, typing minikube service my-service will automatically open the Hello World application in a browser.

   The response to a successful request is a hello message:

   Hello Kubernetes!
   

Cleaning up

To delete the Service, enter this command:

kubectl delete services my-service

To delete the Deployment, the ReplicaSet, and the Pods that are running the Hello World application, enter this command:

kubectl delete deployment hello-world

What's next

Learn more about connecting applications with services.

5.2 - Example: Deploying PHP Guestbook application with Redis

This tutorial shows you how to build and deploy a simple (not production ready), multi-tier web application using Kubernetes and Docker. This example consists of the following components:

• A single-instance Redis to store guestbook entries
• Multiple web frontend instances

Objectives

• Start up a Redis leader.
• Start up two Redis followers.
• Start up the guestbook frontend.
• Expose and view the Frontend Service.
• Clean up.

Before you begin

You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. If you do not already have a cluster, you can create one by using minikube or you can use one of these Kubernetes playgrounds:

• Killercoda
• Play with Kubernetes

Start up the Redis Database

The guestbook application uses Redis to store its data.

Creating the Redis Deployment

The manifest file, included below, specifies a Deployment controller that runs a single replica Redis Pod.

application/guestbook/redis-leader-deployment.yaml

# SOURCE: https://cloud.google.com/kubernetes-engine/docs/tutorials/guestbook
apiVersion: apps/v1
kind: Deployment
metadata:
  name: redis-leader
  labels:
    app: redis
    role: leader
    tier: backend
spec:
  replicas: 1
  selector:
    matchLabels:
      app: redis
  template:
    metadata:
      labels:
        app: redis
        role: leader
        tier: backend
    spec:
      containers:
      - name: leader
        image: "docker.io/redis:6.0.5"
        resources:
          requests:
            cpu: 100m
            memory: 100Mi
        ports:
        - containerPort: 6379

1. Launch a terminal window in the directory you downloaded the manifest files.

2. Apply the Redis Deployment from the redis-leader-deployment.yaml file:

   kubectl apply -f https://k8s.io/examples/application/guestbook/redis-leader-deployment.yaml
   

3. Query the list of Pods to verify that the Redis Pod is running:

   kubectl get pods
   

   The response should be similar to this:

   NAME                           READY   STATUS    RESTARTS   AGE
   redis-leader-fb76b4755-xjr2n   1/1     Running   0          13s
   

4. Run the following command to view the logs from the Redis leader Pod:

   kubectl logs -f deployment/redis-leader
   

Creating the Redis leader Service

The guestbook application needs to communicate to the Redis to write its data. You need to apply a Service to proxy the traffic to the Redis Pod. A Service defines a policy to access the Pods.

application/guestbook/redis-leader-service.yaml

# SOURCE: https://cloud.google.com/kubernetes-engine/docs/tutorials/guestbook
apiVersion: v1
kind: Service
metadata:
  name: redis-leader
  labels:
    app: redis
    role: leader
    tier: backend
spec:
  ports:
  - port: 6379
    targetPort: 6379
  selector:
    app: redis
    role: leader
    tier: backend

1. Apply the Redis Service from the following redis-leader-service.yaml file:

   kubectl apply -f https://k8s.io/examples/application/guestbook/redis-leader-service.yaml
   

2. Query the list of Services to verify that the Redis Service is running:

   kubectl get service
   

   The response should be similar to this:

   NAME           TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)    AGE
   kubernetes     ClusterIP   10.0.0.1     <none>        443/TCP    1m
   redis-leader   ClusterIP   10.103.78.24 <none>        6379/TCP   16s
   

Set up Redis followers

Although the Redis leader is a single Pod, you can make it highly available and meet traffic demands by adding a few Redis followers, or replicas.

application/guestbook/redis-follower-deployment.yaml

# SOURCE: https://cloud.google.com/kubernetes-engine/docs/tutorials/guestbook
apiVersion: apps/v1
kind: Deployment
metadata:
  name: redis-follower
  labels:
    app: redis
    role: follower
    tier: backend
spec:
  replicas: 2
  selector:
    matchLabels:
      app: redis
  template:
    metadata:
      labels:
        app: redis
        role: follower
        tier: backend
    spec:
      containers:
      - name: follower
        image: us-docker.pkg.dev/google-samples/containers/gke/gb-redis-follower:v2
        resources:
          requests:
            cpu: 100m
            memory: 100Mi
        ports:
        - containerPort: 6379

1. Apply the Redis Deployment from the following redis-follower-deployment.yaml file:

   kubectl apply -f https://k8s.io/examples/application/guestbook/redis-follower-deployment.yaml
   

2. Verify that the two Redis follower replicas are running by querying the list of Pods:

   kubectl get pods
   

   The response should be similar to this:

   NAME                             READY   STATUS    RESTARTS   AGE
   redis-follower-dddfbdcc9-82sfr   1/1     Running   0          37s
   redis-follower-dddfbdcc9-qrt5k   1/1     Running   0          38s
   redis-leader-fb76b4755-xjr2n     1/1     Running   0          11m
   

Creating the Redis follower service

The guestbook application needs to communicate with the Redis followers to read data. To make the Redis followers discoverable, you must set up another Service.

application/guestbook/redis-follower-service.yaml

# SOURCE: https://cloud.google.com/kubernetes-engine/docs/tutorials/guestbook
apiVersion: v1
kind: Service
metadata:
  name: redis-follower
  labels:
    app: redis
    role: follower
    tier: backend
spec:
  ports:
    # the port that this service should serve on
  - port: 6379
  selector:
    app: redis
    role: follower
    tier: backend

1. Apply the Redis Service from the following redis-follower-service.yaml file:

   kubectl apply -f https://k8s.io/examples/application/guestbook/redis-follower-service.yaml
   

2. Query the list of Services to verify that the Redis Service is running:

   kubectl get service
   

   The response should be similar to this:

   NAME             TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)    AGE
   kubernetes       ClusterIP   10.96.0.1       <none>        443/TCP    3d19h
   redis-follower   ClusterIP   10.110.162.42   <none>        6379/TCP   9s
   redis-leader     ClusterIP   10.103.78.24    <none>        6379/TCP   6m10s
   

Set up and Expose the Guestbook Frontend

Now that you have the Redis storage of your guestbook up and running, start the guestbook web servers. Like the Redis followers, the frontend is deployed using a Kubernetes Deployment.

The guestbook app uses a PHP frontend. It is configured to communicate with either the Redis follower or leader Services, depending on whether the request is a read or a write. The frontend exposes a JSON interface, and serves a jQuery-Ajax-based UX.

Creating the Guestbook Frontend Deployment

application/guestbook/frontend-deployment.yaml

# SOURCE: https://cloud.google.com/kubernetes-engine/docs/tutorials/guestbook
apiVersion: apps/v1
kind: Deployment
metadata:
  name: frontend
spec:
  replicas: 3
  selector:
    matchLabels:
        app: guestbook
        tier: frontend
  template:
    metadata:
      labels:
        app: guestbook
        tier: frontend
    spec:
      containers:
      - name: php-redis
        image: us-docker.pkg.dev/google-samples/containers/gke/gb-frontend:v5
        env:
        - name: GET_HOSTS_FROM
          value: "dns"
        resources:
          requests:
            cpu: 100m
            memory: 100Mi
        ports:
        - containerPort: 80

1. Apply the frontend Deployment from the frontend-deployment.yaml file:

   kubectl apply -f https://k8s.io/examples/application/guestbook/frontend-deployment.yaml
   

2. Query the list of Pods to verify that the three frontend replicas are running:

   kubectl get pods -l app=guestbook -l tier=frontend
   

   The response should be similar to this:

   NAME                        READY   STATUS    RESTARTS   AGE
   frontend-85595f5bf9-5tqhb   1/1     Running   0          47s
   frontend-85595f5bf9-qbzwm   1/1     Running   0          47s
   frontend-85595f5bf9-zchwc   1/1     Running   0          47s
   

Creating the Frontend Service

The Redis Services you applied is only accessible within the Kubernetes cluster because the default type for a Service is ClusterIP. ClusterIP provides a single IP address for the set of Pods the Service is pointing to. This IP address is accessible only within the cluster.

If you want guests to be able to access your guestbook, you must configure the frontend Service to be externally visible, so a client can request the Service from outside the Kubernetes cluster. However a Kubernetes user can use kubectl port-forward to access the service even though it uses a ClusterIP.

application/guestbook/frontend-service.yaml

# SOURCE: https://cloud.google.com/kubernetes-engine/docs/tutorials/guestbook
apiVersion: v1
kind: Service
metadata:
  name: frontend
  labels:
    app: guestbook
    tier: frontend
spec:
  # if your cluster supports it, uncomment the following to automatically create
  # an external load-balanced IP for the frontend service.
  # type: LoadBalancer
  #type: LoadBalancer
  ports:
    # the port that this service should serve on
  - port: 80
  selector:
    app: guestbook
    tier: frontend

1. Apply the frontend Service from the frontend-service.yaml file:

   kubectl apply -f https://k8s.io/examples/application/guestbook/frontend-service.yaml
   

2. Query the list of Services to verify that the frontend Service is running:

   kubectl get services
   

   The response should be similar to this:

   NAME             TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)    AGE
   frontend         ClusterIP   10.97.28.230    <none>        80/TCP     19s
   kubernetes       ClusterIP   10.96.0.1       <none>        443/TCP    3d19h
   redis-follower   ClusterIP   10.110.162.42   <none>        6379/TCP   5m48s
   redis-leader     ClusterIP   10.103.78.24    <none>        6379/TCP   11m
   

Viewing the Frontend Service via kubectl port-forward

1. Run the following command to forward port 8080 on your local machine to port 80 on the service.

   kubectl port-forward svc/frontend 8080:80
   

   The response should be similar to this:

   Forwarding from 127.0.0.1:8080 -> 80
   Forwarding from [::1]:8080 -> 80
   

2. load the page http://localhost:8080 in your browser to view your guestbook.

Viewing the Frontend Service via LoadBalancer

If you deployed the frontend-service.yaml manifest with type: LoadBalancer you need to find the IP address to view your Guestbook.

1. Run the following command to get the IP address for the frontend Service.

   kubectl get service frontend
   

   The response should be similar to this:

   NAME       TYPE           CLUSTER-IP      EXTERNAL-IP        PORT(S)        AGE
   frontend   LoadBalancer   10.51.242.136   109.197.92.229     80:32372/TCP   1m
   

2. Copy the external IP address, and load the page in your browser to view your guestbook.

Scale the Web Frontend

You can scale up or down as needed because your servers are defined as a Service that uses a Deployment controller.

1. Run the following command to scale up the number of frontend Pods:

   kubectl scale deployment frontend --replicas=5
   

2. Query the list of Pods to verify the number of frontend Pods running:

   kubectl get pods
   

   The response should look similar to this:

   NAME                             READY   STATUS    RESTARTS   AGE
   frontend-85595f5bf9-5df5m        1/1     Running   0          83s
   frontend-85595f5bf9-7zmg5        1/1     Running   0          83s
   frontend-85595f5bf9-cpskg        1/1     Running   0          15m
   frontend-85595f5bf9-l2l54        1/1     Running   0          14m
   frontend-85595f5bf9-l9c8z        1/1     Running   0          14m
   redis-follower-dddfbdcc9-82sfr   1/1     Running   0          97m
   redis-follower-dddfbdcc9-qrt5k   1/1     Running   0          97m
   redis-leader-fb76b4755-xjr2n     1/1     Running   0          108m
   

3. Run the following command to scale down the number of frontend Pods:

   kubectl scale deployment frontend --replicas=2
   

4. Query the list of Pods to verify the number of frontend Pods running:

   kubectl get pods
   

   The response should look similar to this:

   NAME                             READY   STATUS    RESTARTS   AGE
   frontend-85595f5bf9-cpskg        1/1     Running   0          16m
   frontend-85595f5bf9-l9c8z        1/1     Running   0          15m
   redis-follower-dddfbdcc9-82sfr   1/1     Running   0          98m
   redis-follower-dddfbdcc9-qrt5k   1/1     Running   0          98m
   redis-leader-fb76b4755-xjr2n     1/1     Running   0          109m
   

Cleaning up

Deleting the Deployments and Services also deletes any running Pods. Use labels to delete multiple resources with one command.

1. Run the following commands to delete all Pods, Deployments, and Services.

   kubectl delete deployment -l app=redis
   kubectl delete service -l app=redis
   kubectl delete deployment frontend
   kubectl delete service frontend
   

   The response should look similar to this:

   deployment.apps "redis-follower" deleted
   deployment.apps "redis-leader" deleted
   deployment.apps "frontend" deleted
   service "frontend" deleted
   

2. Query the list of Pods to verify that no Pods are running:

   kubectl get pods
   

   The response should look similar to this:

   No resources found in default namespace.
   

What's next

• Complete the Kubernetes Basics Interactive Tutorials
• Use Kubernetes to create a blog using Persistent Volumes for MySQL and Wordpress
• Read more about connecting applications with services
• Read more about using labels effectively

6 - Stateful Applications

6.1 - StatefulSet Basics

This tutorial provides an introduction to managing applications with StatefulSets. It demonstrates how to create, delete, scale, and update the Pods of StatefulSets.

Before you begin

Before you begin this tutorial, you should familiarize yourself with the following Kubernetes concepts:

• Pods
• Cluster DNS
• Headless Services
• PersistentVolumes
• PersistentVolume Provisioning
• The kubectl command line tool

You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. If you do not already have a cluster, you can create one by using minikube or you can use one of these Kubernetes playgrounds:

• Killercoda
• Play with Kubernetes

You should configure kubectl to use a context that uses the default namespace. If you are using an existing cluster, make sure that it's OK to use that cluster's default namespace to practice. Ideally, practice in a cluster that doesn't run any real workloads.

It's also useful to read the concept page about StatefulSets.

Objectives

StatefulSets are intended to be used with stateful applications and distributed systems. However, the administration of stateful applications and distributed systems on Kubernetes is a broad, complex topic. In order to demonstrate the basic features of a StatefulSet, and not to conflate the former topic with the latter, you will deploy a simple web application using a StatefulSet.

After this tutorial, you will be familiar with the following.

• How to create a StatefulSet
• How a StatefulSet manages its Pods
• How to delete a StatefulSet
• How to scale a StatefulSet
• How to update a StatefulSet's Pods

Creating a StatefulSet

Begin by creating a StatefulSet using the example below. It is similar to the example presented in the StatefulSets concept. It creates a headless Service, nginx, to publish the IP addresses of Pods in the StatefulSet, web.

application/web/web.yaml

apiVersion: v1
kind: Service
metadata:
  name: nginx
  labels:
    app: nginx
spec:
  ports:
  - port: 80
    name: web
  clusterIP: None
  selector:
    app: nginx
---
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: web
spec:
  serviceName: "nginx"
  replicas: 2
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: registry.k8s.io/nginx-slim:0.8
        ports:
        - containerPort: 80
          name: web
        volumeMounts:
        - name: www
          mountPath: /usr/share/nginx/html
  volumeClaimTemplates:
  - metadata:
      name: www
    spec:
      accessModes: [ "ReadWriteOnce" ]
      resources:
        requests:
          storage: 1Gi

You will need to use at least two terminal windows. In the first terminal, use kubectl get to watch the creation of the StatefulSet's Pods.

# use this terminal to run commands that specify --watch
# end this watch when you are asked to start a new watch
kubectl get pods --watch -l app=nginx

In the second terminal, use kubectl apply to create the headless Service and StatefulSet:

kubectl apply -f https://k8s.io/examples/application/web/web.yaml

service/nginx created
statefulset.apps/web created

The command above creates two Pods, each running an NGINX webserver. Get the nginx Service...

kubectl get service nginx

NAME      TYPE         CLUSTER-IP   EXTERNAL-IP   PORT(S)   AGE
nginx     ClusterIP    None         <none>        80/TCP    12s

...then get the web StatefulSet, to verify that both were created successfully:

kubectl get statefulset web

NAME      DESIRED   CURRENT   AGE
web       2         1         20s

Ordered Pod creation

For a StatefulSet with n replicas, when Pods are being deployed, they are created sequentially, ordered from {0..n-1}. Examine the output of the kubectl get command in the first terminal. Eventually, the output will look like the example below.

# Do not start a new watch;
# this should already be running
kubectl get pods --watch -l app=nginx

NAME      READY     STATUS    RESTARTS   AGE
web-0     0/1       Pending   0          0s
web-0     0/1       Pending   0         0s
web-0     0/1       ContainerCreating   0         0s
web-0     1/1       Running   0         19s
web-1     0/1       Pending   0         0s
web-1     0/1       Pending   0         0s
web-1     0/1       ContainerCreating   0         0s
web-1     1/1       Running   0         18s

Notice that the web-1 Pod is not launched until the web-0 Pod is Running (see Pod Phase) and Ready (see type in Pod Conditions).

Pods in a StatefulSet

Pods in a StatefulSet have a unique ordinal index and a stable network identity.

Examining the Pod's ordinal index

Get the StatefulSet's Pods:

kubectl get pods -l app=nginx

NAME      READY     STATUS    RESTARTS   AGE
web-0     1/1       Running   0          1m
web-1     1/1       Running   0          1m

As mentioned in the StatefulSets concept, the Pods in a StatefulSet have a sticky, unique identity. This identity is based on a unique ordinal index that is assigned to each Pod by the StatefulSet controller.
The Pods' names take the form <statefulset name>-<ordinal index>. Since the web StatefulSet has two replicas, it creates two Pods, web-0 and web-1.

Using stable network identities

Each Pod has a stable hostname based on its ordinal index. Use kubectl exec to execute the hostname command in each Pod:

for i in 0 1; do kubectl exec "web-$i" -- sh -c 'hostname'; done

web-0
web-1

Use kubectl run to execute a container that provides the nslookup command from the dnsutils package. Using nslookup on the Pods' hostnames, you can examine their in-cluster DNS addresses:

kubectl run -i --tty --image busybox:1.28 dns-test --restart=Never --rm

which starts a new shell. In that new shell, run:

# Run this in the dns-test container shell
nslookup web-0.nginx

The output is similar to:

Server:    10.0.0.10
Address 1: 10.0.0.10 kube-dns.kube-system.svc.cluster.local

Name:      web-0.nginx
Address 1: 10.244.1.6

nslookup web-1.nginx
Server:    10.0.0.10
Address 1: 10.0.0.10 kube-dns.kube-system.svc.cluster.local

Name:      web-1.nginx
Address 1: 10.244.2.6

(and now exit the container shell: exit)

The CNAME of the headless service points to SRV records (one for each Pod that is Running and Ready). The SRV records point to A record entries that contain the Pods' IP addresses.

In one terminal, watch the StatefulSet's Pods:

# Start a new watch
# End this watch when you've seen that the delete is finished
kubectl get pod --watch -l app=nginx

In a second terminal, use kubectl delete to delete all the Pods in the StatefulSet:

kubectl delete pod -l app=nginx

pod "web-0" deleted
pod "web-1" deleted

Wait for the StatefulSet to restart them, and for both Pods to transition to Running and Ready:

# This should already be running
kubectl get pod --watch -l app=nginx

NAME      READY     STATUS              RESTARTS   AGE
web-0     0/1       ContainerCreating   0          0s
NAME      READY     STATUS    RESTARTS   AGE
web-0     1/1       Running   0          2s
web-1     0/1       Pending   0         0s
web-1     0/1       Pending   0         0s
web-1     0/1       ContainerCreating   0         0s
web-1     1/1       Running   0         34s

Use kubectl exec and kubectl run to view the Pods' hostnames and in-cluster DNS entries. First, view the Pods' hostnames:

for i in 0 1; do kubectl exec web-$i -- sh -c 'hostname'; done

web-0
web-1

then, run:

kubectl run -i --tty --image busybox:1.28 dns-test --restart=Never --rm

which starts a new shell.
In that new shell, run:

# Run this in the dns-test container shell
nslookup web-0.nginx

The output is similar to:

Server:    10.0.0.10
Address 1: 10.0.0.10 kube-dns.kube-system.svc.cluster.local

Name:      web-0.nginx
Address 1: 10.244.1.7

nslookup web-1.nginx
Server:    10.0.0.10
Address 1: 10.0.0.10 kube-dns.kube-system.svc.cluster.local

Name:      web-1.nginx
Address 1: 10.244.2.8

(and now exit the container shell: exit)

The Pods' ordinals, hostnames, SRV records, and A record names have not changed, but the IP addresses associated with the Pods may have changed. In the cluster used for this tutorial, they have. This is why it is important not to configure other applications to connect to Pods in a StatefulSet by IP address.

Discovery for specific Pods in a StatefulSet

If you need to find and connect to the active members of a StatefulSet, you should query the CNAME of the headless Service (nginx.default.svc.cluster.local). The SRV records associated with the CNAME will contain only the Pods in the StatefulSet that are Running and Ready.

If your application already implements connection logic that tests for liveness and readiness, you can use the SRV records of the Pods ( web-0.nginx.default.svc.cluster.local, web-1.nginx.default.svc.cluster.local), as they are stable, and your application will be able to discover the Pods' addresses when they transition to Running and Ready.

Writing to stable storage

Get the PersistentVolumeClaims for web-0 and web-1:

kubectl get pvc -l app=nginx

The output is similar to:

NAME        STATUS    VOLUME                                     CAPACITY   ACCESSMODES   AGE
www-web-0   Bound     pvc-15c268c7-b507-11e6-932f-42010a800002   1Gi        RWO           48s
www-web-1   Bound     pvc-15c79307-b507-11e6-932f-42010a800002   1Gi        RWO           48s

The StatefulSet controller created two PersistentVolumeClaims that are bound to two PersistentVolumes.

As the cluster used in this tutorial is configured to dynamically provision PersistentVolumes, the PersistentVolumes were created and bound automatically.

The NGINX webserver, by default, serves an index file from /usr/share/nginx/html/index.html. The volumeMounts field in the StatefulSet's spec ensures that the /usr/share/nginx/html directory is backed by a PersistentVolume.

Write the Pods' hostnames to their index.html files and verify that the NGINX webservers serve the hostnames:

for i in 0 1; do kubectl exec "web-$i" -- sh -c 'echo "$(hostname)" > /usr/share/nginx/html/index.html'; done

for i in 0 1; do kubectl exec -i -t "web-$i" -- curl http://localhost/; done

web-0
web-1

In one terminal, watch the StatefulSet's Pods:

# End this watch when you've reached the end of the section.
# At the start of "Scaling a StatefulSet" you'll start a new watch.
kubectl get pod --watch -l app=nginx

In a second terminal, delete all of the StatefulSet's Pods:

kubectl delete pod -l app=nginx

pod "web-0" deleted
pod "web-1" deleted

Examine the output of the kubectl get command in the first terminal, and wait for all of the Pods to transition to Running and Ready.

# This should already be running
kubectl get pod --watch -l app=nginx

NAME      READY     STATUS              RESTARTS   AGE
web-0     0/1       ContainerCreating   0          0s
NAME      READY     STATUS    RESTARTS   AGE
web-0     1/1       Running   0          2s
web-1     0/1       Pending   0         0s
web-1     0/1       Pending   0         0s
web-1     0/1       ContainerCreating   0         0s
web-1     1/1       Running   0         34s

Verify the web servers continue to serve their hostnames:

for i in 0 1; do kubectl exec -i -t "web-$i" -- curl http://localhost/; done

web-0
web-1

Even though web-0 and web-1 were rescheduled, they continue to serve their hostnames because the PersistentVolumes associated with their PersistentVolumeClaims are remounted to their volumeMounts. No matter what node web-0and web-1 are scheduled on, their PersistentVolumes will be mounted to the appropriate mount points.

Scaling a StatefulSet

Scaling a StatefulSet refers to increasing or decreasing the number of replicas. This is accomplished by updating the replicas field. You can use either kubectl scale or kubectl patch to scale a StatefulSet.

Scaling up

In one terminal window, watch the Pods in the StatefulSet:

# If you already have a watch running, you can continue using that.
# Otherwise, start one.
# End this watch when there are 5 healthy Pods for the StatefulSet
kubectl get pods --watch -l app=nginx

In another terminal window, use kubectl scale to scale the number of replicas to 5:

kubectl scale sts web --replicas=5

statefulset.apps/web scaled

Examine the output of the kubectl get command in the first terminal, and wait for the three additional Pods to transition to Running and Ready.

# This should already be running
kubectl get pod --watch -l app=nginx

NAME      READY     STATUS    RESTARTS   AGE
web-0     1/1       Running   0          2h
web-1     1/1       Running   0          2h
NAME      READY     STATUS    RESTARTS   AGE
web-2     0/1       Pending   0          0s
web-2     0/1       Pending   0         0s
web-2     0/1       ContainerCreating   0         0s
web-2     1/1       Running   0         19s
web-3     0/1       Pending   0         0s
web-3     0/1       Pending   0         0s
web-3     0/1       ContainerCreating   0         0s
web-3     1/1       Running   0         18s
web-4     0/1       Pending   0         0s
web-4     0/1       Pending   0         0s
web-4     0/1       ContainerCreating   0         0s
web-4     1/1       Running   0         19s

The StatefulSet controller scaled the number of replicas. As with StatefulSet creation, the StatefulSet controller created each Pod sequentially with respect to its ordinal index, and it waited for each Pod's predecessor to be Running and Ready before launching the subsequent Pod.

Scaling down

In one terminal, watch the StatefulSet's Pods:

# End this watch when there are only 3 Pods for the StatefulSet
kubectl get pod --watch -l app=nginx

In another terminal, use kubectl patch to scale the StatefulSet back down to three replicas:

kubectl patch sts web -p '{"spec":{"replicas":3}}'

statefulset.apps/web patched

Wait for web-4 and web-3 to transition to Terminating.

# This should already be running
kubectl get pods --watch -l app=nginx

NAME      READY     STATUS              RESTARTS   AGE
web-0     1/1       Running             0          3h
web-1     1/1       Running             0          3h
web-2     1/1       Running             0          55s
web-3     1/1       Running             0          36s
web-4     0/1       ContainerCreating   0          18s
NAME      READY     STATUS    RESTARTS   AGE
web-4     1/1       Running   0          19s
web-4     1/1       Terminating   0         24s
web-4     1/1       Terminating   0         24s
web-3     1/1       Terminating   0         42s
web-3     1/1       Terminating   0         42s

Ordered Pod termination

The controller deleted one Pod at a time, in reverse order with respect to its ordinal index, and it waited for each to be completely shutdown before deleting the next.

Get the StatefulSet's PersistentVolumeClaims:

kubectl get pvc -l app=nginx

NAME        STATUS    VOLUME                                     CAPACITY   ACCESSMODES   AGE
www-web-0   Bound     pvc-15c268c7-b507-11e6-932f-42010a800002   1Gi        RWO           13h
www-web-1   Bound     pvc-15c79307-b507-11e6-932f-42010a800002   1Gi        RWO           13h
www-web-2   Bound     pvc-e1125b27-b508-11e6-932f-42010a800002   1Gi        RWO           13h
www-web-3   Bound     pvc-e1176df6-b508-11e6-932f-42010a800002   1Gi        RWO           13h
www-web-4   Bound     pvc-e11bb5f8-b508-11e6-932f-42010a800002   1Gi        RWO           13h

There are still five PersistentVolumeClaims and five PersistentVolumes. When exploring a Pod's stable storage, we saw that the PersistentVolumes mounted to the Pods of a StatefulSet are not deleted when the StatefulSet's Pods are deleted. This is still true when Pod deletion is caused by scaling the StatefulSet down.

Updating StatefulSets

The StatefulSet controller supports automated updates. The strategy used is determined by the spec.updateStrategy field of the StatefulSet API object. This feature can be used to upgrade the container images, resource requests and/or limits, labels, and annotations of the Pods in a StatefulSet.

There are two valid update strategies, RollingUpdate (the default) and OnDelete.

RollingUpdate

The RollingUpdate update strategy will update all Pods in a StatefulSet, in reverse ordinal order, while respecting the StatefulSet guarantees.

You can split updates to a StatefulSet that uses the RollingUpdate strategy into partitions, by specifying .spec.updateStrategy.rollingUpdate.partition. You'll practice that later in this tutorial.

First, try a simple rolling update.

In one terminal window, patch the web StatefulSet to change the container image again:

kubectl patch statefulset web --type='json' -p='[{"op": "replace", "path": "/spec/template/spec/containers/0/image", "value":"gcr.io/google_containers/nginx-slim:0.8"}]'

statefulset.apps/web patched

In another terminal, watch the Pods in the StatefulSet:

# End this watch when the rollout is complete
#
# If you're not sure, leave it running one more minute
kubectl get pod -l app=nginx --watch

The output is similar to:

NAME      READY     STATUS    RESTARTS   AGE
web-0     1/1       Running   0          7m
web-1     1/1       Running   0          7m
web-2     1/1       Running   0          8m
web-2     1/1       Terminating   0         8m
web-2     1/1       Terminating   0         8m
web-2     0/1       Terminating   0         8m
web-2     0/1       Terminating   0         8m
web-2     0/1       Terminating   0         8m
web-2     0/1       Terminating   0         8m
web-2     0/1       Pending   0         0s
web-2     0/1       Pending   0         0s
web-2     0/1       ContainerCreating   0         0s
web-2     1/1       Running   0         19s
web-1     1/1       Terminating   0         8m
web-1     0/1       Terminating   0         8m
web-1     0/1       Terminating   0         8m
web-1     0/1       Terminating   0         8m
web-1     0/1       Pending   0         0s
web-1     0/1       Pending   0         0s
web-1     0/1       ContainerCreating   0         0s
web-1     1/1       Running   0         6s
web-0     1/1       Terminating   0         7m
web-0     1/1       Terminating   0         7m
web-0     0/1       Terminating   0         7m
web-0     0/1       Terminating   0         7m
web-0     0/1       Terminating   0         7m
web-0     0/1       Terminating   0         7m
web-0     0/1       Pending   0         0s
web-0     0/1       Pending   0         0s
web-0     0/1       ContainerCreating   0         0s
web-0     1/1       Running   0         10s

The Pods in the StatefulSet are updated in reverse ordinal order. The StatefulSet controller terminates each Pod, and waits for it to transition to Running and Ready prior to updating the next Pod. Note that, even though the StatefulSet controller will not proceed to update the next Pod until its ordinal successor is Running and Ready, it will restore any Pod that fails during the update to that Pod's existing version.

Pods that have already received the update will be restored to the updated version, and Pods that have not yet received the update will be restored to the previous version. In this way, the controller attempts to continue to keep the application healthy and the update consistent in the presence of intermittent failures.

Get the Pods to view their container images:

for p in 0 1 2; do kubectl get pod "web-$p" --template '{{range $i, $c := .spec.containers}}{{$c.image}}{{end}}'; echo; done

registry.k8s.io/nginx-slim:0.8
registry.k8s.io/nginx-slim:0.8
registry.k8s.io/nginx-slim:0.8

All the Pods in the StatefulSet are now running the previous container image.

Staging an update

You can split updates to a StatefulSet that uses the RollingUpdate strategy into partitions, by specifying .spec.updateStrategy.rollingUpdate.partition.

For more context, you can read Partitioned rolling updates in the StatefulSet concept page.

You can stage an update to a StatefulSet by using the partition field within .spec.updateStrategy.rollingUpdate. For this update, you will keep the existing Pods in the StatefulSet unchanged whilst you change the pod template for the StatefulSet. Then you - or, outside of a tutorial, some external automation - can trigger that prepared update.

First, patch the web StatefulSet to add a partition to the updateStrategy field:

# The value of "partition" determines which ordinals a change applies to
# Make sure to use a number bigger than the last ordinal for the
# StatefulSet
kubectl patch statefulset web -p '{"spec":{"updateStrategy":{"type":"RollingUpdate","rollingUpdate":{"partition":3}}}}'

statefulset.apps/web patched

Patch the StatefulSet again to change the container image that this StatefulSet uses:

kubectl patch statefulset web --type='json' -p='[{"op": "replace", "path": "/spec/template/spec/containers/0/image", "value":"registry.k8s.io/nginx-slim:0.7"}]'

statefulset.apps/web patched

Delete a Pod in the StatefulSet:

kubectl delete pod web-2

pod "web-2" deleted

Wait for the replacement web-2 Pod to be Running and Ready:

# End the watch when you see that web-2 is healthy
kubectl get pod -l app=nginx --watch

NAME      READY     STATUS              RESTARTS   AGE
web-0     1/1       Running             0          4m
web-1     1/1       Running             0          4m
web-2     0/1       ContainerCreating   0          11s
web-2     1/1       Running   0         18s

Get the Pod's container image:

kubectl get pod web-2 --template '{{range $i, $c := .spec.containers}}{{$c.image}}{{end}}'

registry.k8s.io/nginx-slim:0.8

Notice that, even though the update strategy is RollingUpdate the StatefulSet restored the Pod with the original container image. This is because the ordinal of the Pod is less than the partition specified by the updateStrategy.

Rolling out a canary

You're now going to try a canary rollout of that staged change.

You can roll out a canary (to test the modified template) by decrementing the partition you specified above.

Patch the StatefulSet to decrement the partition:

# The value of "partition" should match the highest existing ordinal for
# the StatefulSet
kubectl patch statefulset web -p '{"spec":{"updateStrategy":{"type":"RollingUpdate","rollingUpdate":{"partition":2}}}}'

statefulset.apps/web patched

The control plane triggers replacement for web-2 (implemented by a graceful delete followed by creating a new Pod once the deletion is complete). Wait for the new web-2 Pod to be Running and Ready.

# This should already be running
kubectl get pod -l app=nginx --watch

NAME      READY     STATUS              RESTARTS   AGE
web-0     1/1       Running             0          4m
web-1     1/1       Running             0          4m
web-2     0/1       ContainerCreating   0          11s
web-2     1/1       Running   0         18s

Get the Pod's container:

kubectl get pod web-2 --template '{{range $i, $c := .spec.containers}}{{$c.image}}{{end}}'

registry.k8s.io/nginx-slim:0.7

When you changed the partition, the StatefulSet controller automatically updated the web-2 Pod because the Pod's ordinal was greater than or equal to the partition.

Delete the web-1 Pod:

kubectl delete pod web-1

pod "web-1" deleted

Wait for the web-1 Pod to be Running and Ready.

# This should already be running
kubectl get pod -l app=nginx --watch

The output is similar to:

NAME      READY     STATUS        RESTARTS   AGE
web-0     1/1       Running       0          6m
web-1     0/1       Terminating   0          6m
web-2     1/1       Running       0          2m
web-1     0/1       Terminating   0         6m
web-1     0/1       Terminating   0         6m
web-1     0/1       Terminating   0         6m
web-1     0/1       Pending   0         0s
web-1     0/1       Pending   0         0s
web-1     0/1       ContainerCreating   0         0s
web-1     1/1       Running   0         18s

Get the web-1 Pod's container image:

kubectl get pod web-1 --template '{{range $i, $c := .spec.containers}}{{$c.image}}{{end}}'

registry.k8s.io/nginx-slim:0.8

web-1 was restored to its original configuration because the Pod's ordinal was less than the partition. When a partition is specified, all Pods with an ordinal that is greater than or equal to the partition will be updated when the StatefulSet's .spec.template is updated. If a Pod that has an ordinal less than the partition is deleted or otherwise terminated, it will be restored to its original configuration.

Phased roll outs

You can perform a phased roll out (e.g. a linear, geometric, or exponential roll out) using a partitioned rolling update in a similar manner to how you rolled out a canary. To perform a phased roll out, set the partition to the ordinal at which you want the controller to pause the update.

The partition is currently set to 2. Set the partition to 0:

kubectl patch statefulset web -p '{"spec":{"updateStrategy":{"type":"RollingUpdate","rollingUpdate":{"partition":0}}}}'

statefulset.apps/web patched

Wait for all of the Pods in the StatefulSet to become Running and Ready.

# This should already be running
kubectl get pod -l app=nginx --watch

The output is similar to:

NAME      READY     STATUS              RESTARTS   AGE
web-0     1/1       Running             0          3m
web-1     0/1       ContainerCreating   0          11s
web-2     1/1       Running             0          2m
web-1     1/1       Running   0         18s
web-0     1/1       Terminating   0         3m
web-0     1/1       Terminating   0         3m
web-0     0/1       Terminating   0         3m
web-0     0/1       Terminating   0         3m
web-0     0/1       Terminating   0         3m
web-0     0/1       Terminating   0         3m
web-0     0/1       Pending   0         0s
web-0     0/1       Pending   0         0s
web-0     0/1       ContainerCreating   0         0s
web-0     1/1       Running   0         3s

Get the container image details for the Pods in the StatefulSet:

for p in 0 1 2; do kubectl get pod "web-$p" --template '{{range $i, $c := .spec.containers}}{{$c.image}}{{end}}'; echo; done

registry.k8s.io/nginx-slim:0.7
registry.k8s.io/nginx-slim:0.7
registry.k8s.io/nginx-slim:0.7

By moving the partition to 0, you allowed the StatefulSet to continue the update process.

OnDelete

You select this update strategy for a StatefulSet by setting the .spec.template.updateStrategy.type to OnDelete.

Patch the web StatefulSet to use the OnDelete update strategy:

kubectl patch statefulset web -p '{"spec":{"updateStrategy":{"type":"OnDelete"}}}'

statefulset.apps/web patched

When you select this update strategy, the StatefulSet controller does not automatically update Pods when a modification is made to the StatefulSet's .spec.template field. You need to manage the rollout yourself - either manually, or using separate automation.

Deleting StatefulSets

StatefulSet supports both non-cascading and cascading deletion. In a non-cascading delete, the StatefulSet's Pods are not deleted when the StatefulSet is deleted. In a cascading delete, both the StatefulSet and its Pods are deleted.

Read Use Cascading Deletion in a Cluster to learn about cascading deletion generally.

Non-cascading delete

In one terminal window, watch the Pods in the StatefulSet.

# End this watch when there are no Pods for the StatefulSet
kubectl get pods --watch -l app=nginx

Use kubectl delete to delete the StatefulSet. Make sure to supply the --cascade=orphan parameter to the command. This parameter tells Kubernetes to only delete the StatefulSet, and to not delete any of its Pods.

kubectl delete statefulset web --cascade=orphan

statefulset.apps "web" deleted

Get the Pods, to examine their status:

kubectl get pods -l app=nginx

NAME      READY     STATUS    RESTARTS   AGE
web-0     1/1       Running   0          6m
web-1     1/1       Running   0          7m
web-2     1/1       Running   0          5m

Even though web has been deleted, all of the Pods are still Running and Ready. Delete web-0:

kubectl delete pod web-0

pod "web-0" deleted

Get the StatefulSet's Pods:

kubectl get pods -l app=nginx

NAME      READY     STATUS    RESTARTS   AGE
web-1     1/1       Running   0          10m
web-2     1/1       Running   0          7m

As the web StatefulSet has been deleted, web-0 has not been relaunched.

In one terminal, watch the StatefulSet's Pods.

# Leave this watch running until the next time you start a watch
kubectl get pods --watch -l app=nginx

In a second terminal, recreate the StatefulSet. Note that, unless you deleted the nginx Service (which you should not have), you will see an error indicating that the Service already exists.

kubectl apply -f https://k8s.io/examples/application/web/web.yaml

statefulset.apps/web created
service/nginx unchanged

Ignore the error. It only indicates that an attempt was made to create the nginx headless Service even though that Service already exists.

Examine the output of the kubectl get command running in the first terminal.

# This should already be running
kubectl get pods --watch -l app=nginx

NAME      READY     STATUS    RESTARTS   AGE
web-1     1/1       Running   0          16m
web-2     1/1       Running   0          2m
NAME      READY     STATUS    RESTARTS   AGE
web-0     0/1       Pending   0          0s
web-0     0/1       Pending   0         0s
web-0     0/1       ContainerCreating   0         0s
web-0     1/1       Running   0         18s
web-2     1/1       Terminating   0         3m
web-2     0/1       Terminating   0         3m
web-2     0/1       Terminating   0         3m
web-2     0/1       Terminating   0         3m

When the web StatefulSet was recreated, it first relaunched web-0. Since web-1 was already Running and Ready, when web-0 transitioned to Running and Ready, it adopted this Pod. Since you recreated the StatefulSet with replicas equal to 2, once web-0 had been recreated, and once web-1 had been determined to already be Running and Ready, web-2 was terminated.

Now take another look at the contents of the index.html file served by the Pods' webservers:

for i in 0 1; do kubectl exec -i -t "web-$i" -- curl http://localhost/; done

web-0
web-1

Even though you deleted both the StatefulSet and the web-0 Pod, it still serves the hostname originally entered into its index.html file. This is because the StatefulSet never deletes the PersistentVolumes associated with a Pod. When you recreated the StatefulSet and it relaunched web-0, its original PersistentVolume was remounted.

Cascading delete

In one terminal window, watch the Pods in the StatefulSet.

# Leave this running until the next page section
kubectl get pods --watch -l app=nginx

In another terminal, delete the StatefulSet again. This time, omit the --cascade=orphan parameter.

kubectl delete statefulset web

statefulset.apps "web" deleted

Examine the output of the kubectl get command running in the first terminal, and wait for all of the Pods to transition to Terminating.

# This should already be running
kubectl get pods --watch -l app=nginx

NAME      READY     STATUS    RESTARTS   AGE
web-0     1/1       Running   0          11m
web-1     1/1       Running   0          27m
NAME      READY     STATUS        RESTARTS   AGE
web-0     1/1       Terminating   0          12m
web-1     1/1       Terminating   0         29m
web-0     0/1       Terminating   0         12m
web-0     0/1       Terminating   0         12m
web-0     0/1       Terminating   0         12m
web-1     0/1       Terminating   0         29m
web-1     0/1       Terminating   0         29m
web-1     0/1       Terminating   0         29m

As you saw in the Scaling Down section, the Pods are terminated one at a time, with respect to the reverse order of their ordinal indices. Before terminating a Pod, the StatefulSet controller waits for the Pod's successor to be completely terminated.

kubectl delete service nginx

service "nginx" deleted

Recreate the StatefulSet and headless Service one more time:

kubectl apply -f https://k8s.io/examples/application/web/web.yaml

service/nginx created
statefulset.apps/web created

When all of the StatefulSet's Pods transition to Running and Ready, retrieve the contents of their index.html files:

for i in 0 1; do kubectl exec -i -t "web-$i" -- curl http://localhost/; done

web-0
web-1

Even though you completely deleted the StatefulSet, and all of its Pods, the Pods are recreated with their PersistentVolumes mounted, and web-0 and web-1 continue to serve their hostnames.

Finally, delete the nginx Service...

kubectl delete service nginx

service "nginx" deleted

...and the web StatefulSet:

kubectl delete statefulset web

statefulset "web" deleted

Pod management policy

For some distributed systems, the StatefulSet ordering guarantees are unnecessary and/or undesirable. These systems require only uniqueness and identity.

You can specify a Pod management policy to avoid this strict ordering; either OrderedReady (the default) or Parallel.

Parallel Pod management

Parallel pod management tells the StatefulSet controller to launch or terminate all Pods in parallel, and not to wait for Pods to become Running and Ready or completely terminated prior to launching or terminating another Pod. This option only affects the behavior for scaling operations. Updates are not affected.

application/web/web-parallel.yaml

apiVersion: v1
kind: Service
metadata:
  name: nginx
  labels:
    app: nginx
spec:
  ports:
  - port: 80
    name: web
  clusterIP: None
  selector:
    app: nginx
---
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: web
spec:
  serviceName: "nginx"
  podManagementPolicy: "Parallel"
  replicas: 2
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: registry.k8s.io/nginx-slim:0.8
        ports:
        - containerPort: 80
          name: web
        volumeMounts:
        - name: www
          mountPath: /usr/share/nginx/html
  volumeClaimTemplates:
  - metadata:
      name: www
    spec:
      accessModes: [ "ReadWriteOnce" ]
      resources:
        requests:
          storage: 1Gi

This manifest is identical to the one you downloaded above except that the .spec.podManagementPolicy of the web StatefulSet is set to Parallel.

In one terminal, watch the Pods in the StatefulSet.

# Leave this watch running until the end of the section
kubectl get pod -l app=nginx --watch

In another terminal, create the StatefulSet and Service in the manifest:

kubectl apply -f https://k8s.io/examples/application/web/web-parallel.yaml

service/nginx created
statefulset.apps/web created

Examine the output of the kubectl get command that you executed in the first terminal.

# This should already be running
kubectl get pod -l app=nginx --watch

NAME      READY     STATUS    RESTARTS   AGE
web-0     0/1       Pending   0          0s
web-0     0/1       Pending   0         0s
web-1     0/1       Pending   0         0s
web-1     0/1       Pending   0         0s
web-0     0/1       ContainerCreating   0         0s
web-1     0/1       ContainerCreating   0         0s
web-0     1/1       Running   0         10s
web-1     1/1       Running   0         10s

The StatefulSet controller launched both web-0 and web-1 at almost the same time.

Keep the second terminal open, and, in another terminal window scale the StatefulSet:

kubectl scale statefulset/web --replicas=4

statefulset.apps/web scaled

Examine the output of the terminal where the kubectl get command is running.

web-3     0/1       Pending   0         0s
web-3     0/1       Pending   0         0s
web-3     0/1       Pending   0         7s
web-3     0/1       ContainerCreating   0         7s
web-2     1/1       Running   0         10s
web-3     1/1       Running   0         26s

The StatefulSet launched two new Pods, and it did not wait for the first to become Running and Ready prior to launching the second.

Cleaning up

You should have two terminals open, ready for you to run kubectl commands as part of cleanup.

kubectl delete sts web
# sts is an abbreviation for statefulset

You can watch kubectl get to see those Pods being deleted.

# end the watch when you've seen what you need to
kubectl get pod -l app=nginx --watch

web-3     1/1       Terminating   0         9m
web-2     1/1       Terminating   0         9m
web-3     1/1       Terminating   0         9m
web-2     1/1       Terminating   0         9m
web-1     1/1       Terminating   0         44m
web-0     1/1       Terminating   0         44m
web-0     0/1       Terminating   0         44m
web-3     0/1       Terminating   0         9m
web-2     0/1       Terminating   0         9m
web-1     0/1       Terminating   0         44m
web-0     0/1       Terminating   0         44m
web-2     0/1       Terminating   0         9m
web-2     0/1       Terminating   0         9m
web-2     0/1       Terminating   0         9m
web-1     0/1       Terminating   0         44m
web-1     0/1       Terminating   0         44m
web-1     0/1       Terminating   0         44m
web-0     0/1       Terminating   0         44m
web-0     0/1       Terminating   0         44m
web-0     0/1       Terminating   0         44m
web-3     0/1       Terminating   0         9m
web-3     0/1       Terminating   0         9m
web-3     0/1       Terminating   0         9m

During deletion, a StatefulSet removes all Pods concurrently; it does not wait for a Pod's ordinal successor to terminate prior to deleting that Pod.

Close the terminal where the kubectl get command is running and delete the nginx Service:

kubectl delete svc nginx

Delete the persistent storage media for the PersistentVolumes used in this tutorial.

kubectl get pvc

NAME        STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGE
www-web-0   Bound    pvc-2bf00408-d366-4a12-bad0-1869c65d0bee   1Gi        RWO            standard       25m
www-web-1   Bound    pvc-ba3bfe9c-413e-4b95-a2c0-3ea8a54dbab4   1Gi        RWO            standard       24m
www-web-2   Bound    pvc-cba6cfa6-3a47-486b-a138-db5930207eaf   1Gi        RWO            standard       15m
www-web-3   Bound    pvc-0c04d7f0-787a-4977-8da3-d9d3a6d8d752   1Gi        RWO            standard       15m
www-web-4   Bound    pvc-b2c73489-e70b-4a4e-9ec1-9eab439aa43e   1Gi        RWO            standard       14m

kubectl get pv

NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS   CLAIM               STORAGECLASS   REASON   AGE
pvc-0c04d7f0-787a-4977-8da3-d9d3a6d8d752   1Gi        RWO            Delete           Bound    default/www-web-3   standard                15m
pvc-2bf00408-d366-4a12-bad0-1869c65d0bee   1Gi        RWO            Delete           Bound    default/www-web-0   standard                25m
pvc-b2c73489-e70b-4a4e-9ec1-9eab439aa43e   1Gi        RWO            Delete           Bound    default/www-web-4   standard                14m
pvc-ba3bfe9c-413e-4b95-a2c0-3ea8a54dbab4   1Gi        RWO            Delete           Bound    default/www-web-1   standard                24m
pvc-cba6cfa6-3a47-486b-a138-db5930207eaf   1Gi        RWO            Delete           Bound    default/www-web-2   standard                15m

kubectl delete pvc www-web-0 www-web-1 www-web-2 www-web-3 www-web-4

persistentvolumeclaim "www-web-0" deleted
persistentvolumeclaim "www-web-1" deleted
persistentvolumeclaim "www-web-2" deleted
persistentvolumeclaim "www-web-3" deleted
persistentvolumeclaim "www-web-4" deleted

kubectl get pvc

No resources found in default namespace.

6.2 - Example: Deploying WordPress and MySQL with Persistent Volumes

This tutorial shows you how to deploy a WordPress site and a MySQL database using Minikube. Both applications use PersistentVolumes and PersistentVolumeClaims to store data.

A PersistentVolume (PV) is a piece of storage in the cluster that has been manually provisioned by an administrator, or dynamically provisioned by Kubernetes using a StorageClass. A PersistentVolumeClaim (PVC) is a request for storage by a user that can be fulfilled by a PV. PersistentVolumes and PersistentVolumeClaims are independent from Pod lifecycles and preserve data through restarting, rescheduling, and even deleting Pods.

Objectives

• Create PersistentVolumeClaims and PersistentVolumes
• Create a kustomization.yaml with
  • a Secret generator
  • MySQL resource configs
  • WordPress resource configs
• Apply the kustomization directory by kubectl apply -k ./
• Clean up

Before you begin

You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. If you do not already have a cluster, you can create one by using minikube or you can use one of these Kubernetes playgrounds:

• Killercoda
• Play with Kubernetes

The example shown on this page works with kubectl 1.27 and above.

Download the following configuration files:

1. mysql-deployment.yaml

2. wordpress-deployment.yaml

Create PersistentVolumeClaims and PersistentVolumes

MySQL and Wordpress each require a PersistentVolume to store data. Their PersistentVolumeClaims will be created at the deployment step.

Many cluster environments have a default StorageClass installed. When a StorageClass is not specified in the PersistentVolumeClaim, the cluster's default StorageClass is used instead.

When a PersistentVolumeClaim is created, a PersistentVolume is dynamically provisioned based on the StorageClass configuration.

Create a kustomization.yaml

Add a Secret generator

A Secret is an object that stores a piece of sensitive data like a password or key. Since 1.14, kubectl supports the management of Kubernetes objects using a kustomization file. You can create a Secret by generators in kustomization.yaml.

Add a Secret generator in kustomization.yaml from the following command. You will need to replace YOUR_PASSWORD with the password you want to use.

cat <<EOF >./kustomization.yaml
secretGenerator:
- name: mysql-pass
  literals:
  - password=YOUR_PASSWORD
EOF

Add resource configs for MySQL and WordPress

The following manifest describes a single-instance MySQL Deployment. The MySQL container mounts the PersistentVolume at /var/lib/mysql. The MYSQL_ROOT_PASSWORD environment variable sets the database password from the Secret.

application/wordpress/mysql-deployment.yaml

apiVersion: v1
kind: Service
metadata:
  name: wordpress-mysql
  labels:
    app: wordpress
spec:
  ports:
    - port: 3306
  selector:
    app: wordpress
    tier: mysql
  clusterIP: None
---
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: mysql-pv-claim
  labels:
    app: wordpress
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 20Gi
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: wordpress-mysql
  labels:
    app: wordpress
spec:
  selector:
    matchLabels:
      app: wordpress
      tier: mysql
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        app: wordpress
        tier: mysql
    spec:
      containers:
      - image: mysql:8.0
        name: mysql
        env:
        - name: MYSQL_ROOT_PASSWORD
          valueFrom:
            secretKeyRef:
              name: mysql-pass
              key: password
        - name: MYSQL_DATABASE
          value: wordpress
        - name: MYSQL_USER
          value: wordpress
        - name: MYSQL_PASSWORD
          valueFrom:
            secretKeyRef:
              name: mysql-pass
              key: password
        ports:
        - containerPort: 3306
          name: mysql
        volumeMounts:
        - name: mysql-persistent-storage
          mountPath: /var/lib/mysql
      volumes:
      - name: mysql-persistent-storage
        persistentVolumeClaim:
          claimName: mysql-pv-claim

The following manifest describes a single-instance WordPress Deployment. The WordPress container mounts the PersistentVolume at /var/www/html for website data files. The WORDPRESS_DB_HOST environment variable sets the name of the MySQL Service defined above, and WordPress will access the database by Service. The WORDPRESS_DB_PASSWORD environment variable sets the database password from the Secret kustomize generated.

application/wordpress/wordpress-deployment.yaml

apiVersion: v1
kind: Service
metadata:
  name: wordpress
  labels:
    app: wordpress
spec:
  ports:
    - port: 80
  selector:
    app: wordpress
    tier: frontend
  type: LoadBalancer
---
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: wp-pv-claim
  labels:
    app: wordpress
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 20Gi
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: wordpress
  labels:
    app: wordpress
spec:
  selector:
    matchLabels:
      app: wordpress
      tier: frontend
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        app: wordpress
        tier: frontend
    spec:
      containers:
      - image: wordpress:6.2.1-apache
        name: wordpress
        env:
        - name: WORDPRESS_DB_HOST
          value: wordpress-mysql
        - name: WORDPRESS_DB_PASSWORD
          valueFrom:
            secretKeyRef:
              name: mysql-pass
              key: password
        - name: WORDPRESS_DB_USER
          value: wordpress
        ports:
        - containerPort: 80
          name: wordpress
        volumeMounts:
        - name: wordpress-persistent-storage
          mountPath: /var/www/html
      volumes:
      - name: wordpress-persistent-storage
        persistentVolumeClaim:
          claimName: wp-pv-claim