Trying to create a Drupal container on Kubernetes with the apache drupal image.

When a persistent volume is mounted at /var/www/html and inspecting the Drupal container with docker exec -it <drupal-container-name> bash there are no files visible. Thus no files can be served.

Workflow

1 - Create google compute disk

gcloud compute disks create --size=20GB --zone=us-central1-c drupal-1

2 - Register the newly created google compute disk to the kubernetes cluster instance

kubectl create -f gce-volumes.yaml

3 - Create Drupal pod

kubectl create -f drupal-deployment.yaml

The definition files are inspired from the wordpress example, my drupal-deployment.yaml:

apiVersion: v1
kind: Service
metadata:
  name: drupal
  labels:
    app: drupal
spec:
  ports:
    - port: 80
  selector:
    app: drupal
    tier: frontend
  type: LoadBalancer
---
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: dp-pv-claim
  labels:
    app: drupal
spec:
  accessModes:
    - ReadWriteOnce
  resources:
      requests:
          storage: 20Gi
---
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: drupal
  labels:
    app: drupal
spec:
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        app: drupal
        tier: frontend
    spec:
      containers:
      - name: drupal
        image: drupal:8.2.3-apache
        ports:
        - name: drupal
          containerPort: 80
        volumeMounts:
        - name: drupal-persistent-storage
          mountPath: /var/www/html
      volumes:
      - name: drupal-persistent-storage
        persistentVolumeClaim:
          claimName: dp-pv-claim

And the gce-volumes.yaml:

apiVersion: v1
kind: PersistentVolume
metadata:
  name: drupal-pv-1
spec:
  capacity:
    storage: 20Gi
  accessModes:
    - ReadWriteOnce
  gcePersistentDisk:
    pdName: drupal-1
    fsType: ext4

What's causing the files to disappear? How can I successfully persist the Drupal installation files at /var/www/html inside the container?