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Step-by-step instructions for performing operations with Kubernetes.

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Configuring a Pod to Use a Volume for Storage

This page shows how to configure a Pod to use a Volume for storage.

A Container’s file system lives only as long as the Container does, so when a Container terminates and restarts, changes to the filesystem are lost. For more consistent storage that is independent of the Container, you can use a Volume. This is especially important for stateful applications, such as key-value stores and databases. For example, Redis is a key-value cache and store.

Before you begin

You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a cluster, you can create one by using Minikube.

Configuring a volume for a Pod

In this exercise, you create a Pod that runs one Container. This Pod has a Volume of type emptyDir that lasts for the life of the Pod, even if the Container terminates and restarts. Here is the configuration file for the Pod:

pod-redis.yaml 
apiVersion: v1
kind: Pod
metadata:
  name: redis
spec:
  containers:
  - name: redis
    image: redis
    volumeMounts:
    - name: redis-storage
      mountPath: /data/redis
  volumes:
  - name: redis-storage
    emptyDir: {}

  1. Create the Pod:

     kubectl create -f http://k8s.io/docs/tasks/configure-pod-container/pod-redis.yaml

  2. Verify that the Pod’s Container is running, and then watch for changes to the Pod:

     kubectl get --watch pod redis

    The output looks like this:

     NAME      READY     STATUS    RESTARTS   AGE
 redis     1/1       Running   0          13s

  3. In another terminal, get a shell to the running Container:

     kubectl exec -it redis -- /bin/bash

  4. In your shell, go to /data/redis, and create a file:

     root@redis:/data/redis# echo Hello > test-file

  5. In your shell, list the running processes:

     root@redis:/data/redis# ps aux

    The output is similar to this:

     USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
 redis        1  0.1  0.1  33308  3828 ?        Ssl  00:46   0:00 redis-server *:6379
 root        12  0.0  0.0  20228  3020 ?        Ss   00:47   0:00 /bin/bash
 root        15  0.0  0.0  17500  2072 ?        R+   00:48   0:00 ps aux

  6. In your shell, kill the redis process:

     root@redis:/data/redis# kill <pid>

    where <pid> is the redis process ID (PID).

  7. In your original terminal, watch for changes to the redis Pod. Eventually, you will see something like this:

     NAME      READY     STATUS     RESTARTS   AGE
 redis     1/1       Running    0          13s
 redis     0/1       Completed  0         6m
 redis     1/1       Running    1         6m

At this point, the Container has terminated and restarted. This is because the redis Pod has a restartPolicy of Always.

  1. Get a shell into the restarted Container:

     kubectl exec -it redis -- /bin/bash

  2. In your shell, goto /data/redis, and verify that test-file is still there.

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