docs/doc/source/storage/kubernetes/storage-configuration-mount-readwriteonce-persistent-volumes-in-containers.rst

Mount ReadWriteOnce Persistent Volumes in Containers

You can attach ReadWriteOnce to a container when launching a container, and changes to those will persist even if that container gets terminated and restarted.

This example shows how a volume is claimed and mounted by a simple running container, and the contents of the volume claim persists across restarts of the container. It is the responsibility of an individual micro-service within an application to make a volume claim, mount it, and use it.

You should refer to the Volume Claim examples. For more information, see, Create ReadWriteOnce Persistent Volume Claims <storage-configuration-create-readwriteonce-persistent-volume-claims>.

1. Create the busybox container with the persistent volumes created from the mounted.

   1. Create a yaml file definition for the busybox container.

      % cat <<EOF > rwo-busybox.yaml
      apiVersion: apps/v1
      kind: Deployment
      metadata:
        name: rwo-busybox
        namespace: default
      spec:
        progressDeadlineSeconds: 600
        replicas: 1
        selector:
          matchLabels:
            run: busybox
        template:
          metadata:
            labels:
              run: busybox
          spec:
            containers:
            - args:
              - sh
              image: busybox
              imagePullPolicy: Always
              name: busybox
              stdin: true
              tty: true
              volumeMounts:
              - name: pvc1
                mountPath: "/mnt1"
              - name: pvc2
                mountPath: "/mnt2"
            restartPolicy: Always
            volumes:
            - name: pvc1
              persistentVolumeClaim:
                claimName: rwo-test-claim1
            - name: pvc2
              persistentVolumeClaim:
                claimName: rwo-test-claim2
      EOF

   2. Apply the busybox configuration.

      % kubectl apply -f rwo-busybox.yaml
      deployment.apps/rwo-busybox created

2. Attach to the busybox and create files on the Persistent Volumes.

   1. List the available pods.

      % kubectl get pods
      NAME                        READY   STATUS    RESTARTS   AGE
      rwo-busybox-5c4f877455-gkg2s 1/1     Running   0         19s

   2. Connect to the pod shell for CLI access.

      % kubectl attach rwo-busybox-5c4f877455-gkg2s -c busybox -i -t

   3. From the container's console, list the disks to verify that the Persistent Volumes are attached.

      # df
      Filesystem     1K-blocks  Used     Available Use% Mounted on
      overlay        31441920   3239984  28201936  10%   /
      tmpfs          65536         0     65536     0%    /dev
      tmpfs          65900776      0     65900776  0%    /sys/fs/cgroup
      /dev/rbd0      999320     2564     980372    0%    /mnt1
      /dev/rbd1      999320     2564     980372    0%    /mnt2
      /dev/sda4      20027216   4952208  14034624  26%

      The PVCs are mounted as /mnt1 and /mnt2.

3. Create files in the mounted volumes.

   # cd /mnt1
   # touch i-was-here
   # ls /mnt1
   i-was-here lost+found
   #
   # cd /mnt2
   # touch i-was-here-too
   # ls /mnt2
   i-was-here-too lost+found

4. End the container session.

   # exit
   Session ended, resume using
   'kubectl attach busybox-5c4f877455-gkg2s -c busybox -i -t' command when
   the pod is running

5. Terminate the busybox container.

   % kubectl delete -f rwo-busybox.yaml

6. Recreate the busybox container, again attached to persistent volumes.

   1. Apply the busybox configuration.

      % kubectl apply -f rwo-busybox.yaml
      deployment.apps/rwo-busybox created

   2. List the available pods.

      % kubectl get pods
      NAME                        READY   STATUS    RESTARTS   AGE
      rwo-busybox-5c4f877455-jgcc4  1/1   Running   0          19s

   3. Connect to the pod shell for CLI access.

      % kubectl attach busybox-5c4f877455-jgcc4 -c busybox -i -t

   4. From the container's console, list the disks to verify that the PVCs are attached.

      # df
      Filesystem           1K-blocks      Used Available Use% Mounted on
      overlay               31441920   3239984  28201936  10% /
      tmpfs                    65536         0     65536   0% /dev
      tmpfs                 65900776         0  65900776   0% /sys/fs/cgroup
      /dev/rbd0               999320      2564    980372   0% /mnt1
      /dev/rbd1               999320      2564    980372   0% /mnt2
      /dev/sda4             20027216   4952208  14034624  26%
      ...

7. Verify that the files created during the earlier container session still exist.

   # ls /mnt1
   i-was-here lost+found
   # ls /mnt2
   i-was-here-too lost+found