Volume not persistent in Google Cloud - mysql

Question

I'm trying to build a mysql pod on Google Cloud. However, when I create a database and then restart the pod, the database that I created is not persisted.
I follow this official tutorial : https://github.com/kubernetes/kubernetes/tree/master/examples/mysql-wordpress-pd
mysql-deployment.yaml :
---
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
name: mysql-pv-claim
labels:
app: myApp
env: production
spec:
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 20Gi
---
kind: Deployment
apiVersion: extensions/v1beta1
metadata:
name: myapp-backend-production-mysql
spec:
replicas:
template:
metadata:
labels:
app: myapp
role: backend
env: production
type: mysql
spec:
containers:
- name: backend-mysql
image: mysql:5.6
env:
- name: MYSQL_ROOT_PASSWORD
valueFrom:
secretKeyRef:
name: mysql-pass
key: password.txt
ports:
- name: backend
containerPort: 3306
volumeMounts:
- name: mysql-persistent-storage
mountPath: /var/lib/mysql
volumes:
- name: mysql-persistent-storage
persistentVolumeClaim:
claimName: mysql-pv-claim
And the volume.yaml :
# Not applied for all build
kind: PersistentVolume
apiVersion: v1
metadata:
name: mysql-production-pv-1
labels:
app: myapp
env: production
spec:
capacity:
storage: 20Gi
accessModes:
- ReadWriteOnce
gcePersistentDisk:
pdName: mysql-production-1
fsType: ext4
---
kind: PersistentVolume
apiVersion: v1
metadata:
name: mysql-production-pv-2
labels:
app: myapp
env: production
spec:
capacity:
storage: 20Gi
accessModes:
- ReadWriteOnce
gcePersistentDisk:
pdName: mysql-production-2
fsType: ext4