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