10.2. Write a PersistentVolumeClaim

In this lab you’ll configure the mysite pod to use the PersistentVolumeClaim that you made in the last lab, 10.1. Persistent Volumes. Using a PersistentVolumeClaim ensures that your valuable user data is kept separately from your pods.

Update the Pod Definition

There are two fragments that you must add to your pod definition in deployment/pod.yaml. The first one goes under the spec key and ensures that the PersistentVolume is available to the machine running the pod:

volumes:
- name: db
  persistentVolumeClaim:
      claimName: mysite-data

The second fragment makes the volume available to a particular container. This one is siblings with image, ports and resources definition under the spec.containers[0] key:

volumeMounts:
- name: db
  mountPath: /data

Redeploy the Pod

You can’t simply update the pod with a volume mount. You have to delete and restart it:

$ kubectl delete pod/mysite-pod
$ kubectl apply -f pod.yaml

Verify that the volume is present:

$ kubectl describe pod/postgres
...
    Mounts:
      /var/lib/postgresql/data from db (rw)
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-vr2qm (ro)
...
Volumes:
  db:
    Type:       PersistentVolumeClaim (a reference to a PersistentVolumeClaim in the same namespace)
    ClaimName:  db
    ReadOnly:   false
  default-token-vr2qm:
    Type:        Secret (a volume populated by a Secret)
    SecretName:  default-token-vr2qm
    Optional:    false

Re-Initialize the Database

Now that the data has moved to its permanent location you have to start the database fresh:

$ kubectl exec --stdin --tty  pod/mysite-pod -- /bin/bash 
root@mysite-pod:/mysite# python manage.py migrate
root@mysite-pod:/mysite# python manage.py createsuperuser 
...