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

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

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

      ~(keystone_admin)]$ 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
      

   2. Apply the busybox configuration.

      ~(keystone_admin)]$ kubectl apply -f wrx-busybox.yaml
      deployment.apps/wrx-busybox created
      

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

   1. List the available pods.

      ~(keystone_admin)]$ kubectl get pods
      NAME                           READY   STATUS    RESTARTS   AGE
      wrx-busybox-767564b9cf-g8ln8   1/1     Running   0          49s
      wrx-busybox-767564b9cf-jrk5z   1/1     Running   0          49s
      

   2. Connect to the pod shell for CLI access.

      kubectl attach wrx-busybox-767564b9cf-g8ln8 -c busybox -i -t
      

   3. 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   9695488  21746432  31% /
      tmpfs                    65536         0     65536   0% /dev
      tmpfs                 12295352         0  12295352   0% /sys/fs/cgroup
      192.168.204.2:6789:/volumes/csi/pvc-volumes-565a1160-7b6c-11ed-84b8-0e99d59ed96d/cf39026c-06fc-413a-bce9-b13fb66254a3
                             1048576         0   1048576   0% /mnt1
      

      The PVC is mounted as /mnt1.

3. Create files in the mount.

   # cd /mnt1
   # touch i-was-here-${HOSTNAME}
   # ls /mnt1
   i-was-here-wrx-busybox-767564b9cf-g8ln8
   

4. End the container session.

   % exit
   Session ended, resume using 'kubectl attach wrx-busybox-767564b9cf-g8ln8 -c busybox -i -t' command when the pod is running
   

5. Connect to the other busybox container

   ~(keystone_admin)]$ kubectl attach wrx-busybox-767564b9cf-jrk5z -i -t
   

6. 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   9695512  21746408  31% /
   tmpfs                    65536         0     65536   0% /dev
   tmpfs                 12295352         0  12295352   0% /sys/fs/cgroup
   192.168.204.2:6789:/volumes/csi/pvc-volumes-565a1160-7b6c-11ed-84b8-0e99d59ed96d/cf39026c-06fc-413a-bce9-b13fb66254a3
                          1048576         0   1048576   0% /mnt1
   

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

   # cd /mnt1
   # ls
   i-was-here-wrx-busybox-767564b9cf-g8ln8
   # echo ${HOSTNAME}
   wrx-busybox-767564b9cf-jrk5z
   # touch i-was-here-${HOSTNAME}
   # ls
   i-was-here-wrx-busybox-767564b9cf-g8ln8  i-was-here-wrx-busybox-767564b9cf-jrk5z
   

8. End the container session.

   % exit
   Session ended, resume using 'kubectl attach wrx-busybox-767564b9cf-jrk5z -c busybox -i -t' command when the pod is running
   

9. Terminate the busybox container.

   ~(keystone_admin)]$ kubectl delete -f wrx-busybox.yaml
   

   For more information on Persistent Volume Support, see, About Persistent Volume Support.