Mount ReadWriteMany Persistent Volumes in Containers¶

You can attach a ReadWriteMany PVC to multiple containers, and that PVC can be written to, by all containers.

About this task

This example shows how a volume is claimed and mounted by each container replica of a deployment with 2 replicas, and each container replica can read and write to the PVC. It is the responsibility of an individual micro-service within an application to make a volume claim, mount it, and use it.

Prerequisites

You must have created the PVCs. This procedure uses PVCs with names and configurations created in StarlingX StarlingX Storage Configuration and Management: Create ReadWriteMany Persistent Volume Claims .

Procedure

Create the busybox container with the persistent volumes created from the PVCs mounted. This deployment will create two replicas mounting the same persistent volume.

Create a yaml file definition for the busybox container.

% cat <<EOF > wrx-busybox.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: wrx-busybox
  namespace: default
spec:
  progressDeadlineSeconds: 600
  replicas: 2
  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"
      restartPolicy: Always
      volumes:
      - name: pvc1
        persistentVolumeClaim:
          claimName: rwx-test-claim
EOF

Apply the busybox configuration.

% kubectl apply -f wrx-busybox.yaml
deployment.apps/wrx-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
wrx-busybox-6455997c76-4kg8v   1/1     Running   0          108s
wrx-busybox-6455997c76-crmw6   1/1     Running   0          108s

Connect to the pod shell for CLI access.

% kubectl attach wrx-busybox-6455997c76-4kg8v -c busybox -i -t

From the container’s console, list the disks to verify that the Persistent Volume is attached.

% df
Filesystem           1K-blocks      Used Available Use% Mounted on
overlay               31441920   1783748  29658172   6% /
tmpfs                    65536         0     65536   0% /dev
tmpfs                  5033188         0   5033188   0% /sys/fs/cgroup
ceph-fuse            516542464    643072 515899392   0% /mnt1

The PVC is mounted as /mnt1.

Create files in the mount.

# cd /mnt1
# touch i-was-here-${HOSTNAME}
# ls /mnt1
i-was-here-wrx-busybox-6455997c76-4kg8vi

End the container session.

% exit
wrx-busybox-6455997c76-4kg8v -c busybox -i -t' command when the pod is running

Connect to the other busybox container

% kubectl attach wrx-busybox-6455997c76-crmw6 -c busybox -i -t

Optional: From the container’s console list the disks to verify that the PVC is attached.

% df
Filesystem           1K-blocks      Used Available Use% Mounted on
overlay               31441920   1783888  29658032   6% /
tmpfs                    65536         0     65536   0% /dev
tmpfs                  5033188         0   5033188   0% /sys/fs/cgroup
ceph-fuse            516542464    643072 515899392   0% /mnt1

Verify that the file created from the other container exists and that this container can also write to the Persistent Volume.

# cd /mnt1
# ls /mnt1
i-was-here-wrx-busybox-6455997c76-4kg8v
# echo ${HOSTNAME}
wrx-busybox-6455997c76-crmw6
# touch i-was-here-${HOSTNAME}
# ls /mnt1
i-was-here-wrx-busybox-6455997c76-4kg8v i-was-here-wrx-busybox-6455997c76-crmw6

End the container session.

% exit
Session ended, resume using 'kubectl attach wrx-busybox-6455997c76-crmw6 -c busybox -i -t' command when the pod is running

Terminate the busybox container.
```
% kubectl delete -f wrx-busybox.yaml
```
For more information on Persistent Volume Support, see, About Persistent Volume Support.