Mount ReadWriteOnce Persistent Volumes in Containers¶

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

Note

A ReadWriteOnce PVC can only be mounted by a single container.

About this task

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.

Prerequisites

You should refer to the Volume Claim examples. For more information, see Create ReadWriteOnce Persistent Volume Claims.

Procedure

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

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

Apply the busybox configuration.

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

Attach to the busybox and create files on the persistent volumes.

List the available pods.

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

Connect to the pod shell for CLI access.

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

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.

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

End the container session.

# exit
Session ended, resume using :command:`kubectl attach busybox-5c4f877455-gkg2s -c busybox -i -t`
when the pod is running

Terminate the busybox container.
```
% kubectl delete -f rwo-busybox.yaml
```

Re-create the busybox container, again attached to persistent volumes.

Apply the busybox configuration.

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

List the available pods.

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

Connect to the pod shell for CLI access.

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

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%
...

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
```

Mount ReadWriteOnce Persistent Volumes in Containers

Mount ReadWriteOnce Persistent Volumes in Containers¶

StarlingX