kubernetes StorageClass does not retain existing data - kubernetes

Question

My Kubernetes StorageClass volume doesn't retain existing data when the pod is deleted and deployed back with my postgresql database. When I delete the pod, the new pod is created but the database is empty.
I have followed variations of the different versions of the tutorials (https://kubernetes.io/docs/concepts/storage/persistent-volumes/) but nothing seems to work.
I paste all the YAML files cause the problem might be in the combination.
storage-google.yaml
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
name: spingular-pvc
spec:
storageClassName: standard
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 7Gi
---
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
name: standard
provisioner: kubernetes.io/gce-pd
parameters:
type: pd-standard
zone: us-east4-a
jhipsterpress-postgresql.yml
apiVersion: v1
kind: Secret
metadata:
name: jhipsterpress-postgresql
namespace: default
labels:
app: jhipsterpress-postgresql
type: Opaque
data:
postgres-password: NjY0NXJxd24=
---
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
name: jhipsterpress-postgresql
namespace: default
spec:
replicas: 1
template:
metadata:
labels:
app: jhipsterpress-postgresql
spec:
volumes:
- name: data
persistentVolumeClaim:
claimName: spingular-pvc
containers:
- name: postgres
image: postgres:10.4
env:
- name: POSTGRES_USER
value: jhipsterpress
- name: POSTGRES_PASSWORD
valueFrom:
secretKeyRef:
name: jhipsterpress-postgresql
key: postgres-password
ports:
- containerPort: 5432
volumeMounts:
- name: data
mountPath: /var/lib/postgresql/
---
apiVersion: v1
kind: Service
metadata:
name: jhipsterpress-postgresql
namespace: default
spec:
selector:
app: jhipsterpress-postgresql
ports:
- name: postgresqlport
port: 5432
type: LoadBalancer
jhipsterpress-deployment.yml
apiVersion: apps/v1
kind: Deployment
metadata:
name: jhipsterpress
namespace: default
spec:
replicas: 1
selector:
matchLabels:
app: jhipsterpress
version: "v1"
template:
metadata:
labels:
app: jhipsterpress
version: "v1"
spec:
initContainers:
- name: init-ds
image: busybox:latest
command:
- '/bin/sh'
- '-c'
- |
while true
do
rt=$(nc -z -w 1 jhipsterpress-postgresql 5432)
if [ $? -eq 0 ]; then
echo "DB is UP"
break
fi
echo "DB is not yet reachable;sleep for 10s before retry"
sleep 10
done
containers:
- name: jhipsterpress-app
image: galore/jhipsterpress
env:
- name: SPRING_PROFILES_ACTIVE
value: prod
- name: SPRING_DATASOURCE_URL
value: jdbc:postgresql://jhipsterpress-postgresql.default.svc.cluster.local:5432/jhipsterpress
- name: SPRING_DATASOURCE_USERNAME
value: jhipsterpress
- name: SPRING_DATASOURCE_PASSWORD
valueFrom:
secretKeyRef:
name: jhipsterpress-postgresql
key: postgres-password
- name: JAVA_OPTS
value: " -Xmx256m -Xms256m"
resources:
requests:
memory: "256Mi"
cpu: "500m"
limits:
memory: "512Mi"
cpu: "1"
ports:
- name: http
containerPort: 8080
readinessProbe:
httpGet:
path: /management/health
port: http
initialDelaySeconds: 20
periodSeconds: 15
failureThreshold: 6
livenessProbe:
httpGet:
path: /management/health
port: http
initialDelaySeconds: 120
jhipsterpress-service.yml
apiVersion: v1
kind: Service
metadata:
name: jhipsterpress
namespace: default
labels:
app: jhipsterpress
spec:
selector:
app: jhipsterpress
type: LoadBalancer
ports:
- name: http
port: 8080
When I included a Retain Policy I was getting this error:
#cloudshell:~ (academic-veld-230622)$ kubectl apply -f storage-google.yaml
error: error validating "storage-google.yaml": error validating data:
ValidationError(PersistentVolumeClaim.spec): unknown field "persistentVolumeReclaimPolicy" in io.k8s.api.core.v1.PersistentVolumeClaimSpec; if you choose to ignore these errors, turn validation off with --validate=false
Please, if you know of a complete example on a public image that works (in postgresql, I can make it work with Mongo), I will really appreciate it.
Thanks to all.

Answer 1

Note that for this to work you need to have your PVC dynamically provision a PV to satisfy its requirements, then there will be a permanent binding between the PVC and PV and every time your workload uses the PVC then it will use the same PV. Specifically indicated by this excerpt:
If a PV was dynamically provisioned for a new PVC, the loop will always bind that PV to the PVC
If in your case the Google Persistent Disk is being provisioned by the PVC, and you can verify that on GCP it's the same PV used every time, then it's probably an issue with the pod startup process where it's removing all the data. (Is there any reason why you are using /var/lib/postgresql/ vs /var/lib/postgresql?)
Also, persistentVolumeReclaimPolicy: Retain applies to a PV, not a PVC. For dynamically provisioned PVs the value is Delete. In your case, it wouldn't apply because your dynamically provisioned volume should be bound to your PVC. In other words, you are not reclaiming the volume.
Having said all that the recommended way to deploy a DB is using StatefulSets similar to this mysql example using a volumeClaimTemplate.