Can we create Multiple databases in Same Persistent Volume in kubernetes ? - postgresql

Question

I have Azure Machine (kubernetes) who have Agent of 2 core, 1 GB. My two services are running on this Machine each have its own Postgres (Deplyment, Service, Pv, PVC).
I want to host my third service too on same machine.
So when I tried to create Postgres Deployment (this too have its own service, PV, PVC) but Pod was stuck in status=ContainerCreating .
After some digging I got to know that my VM only Supports data-disks.
So i thought why not use PVC of earlier deployment in current service like:
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
name: third-postgres
labels:
name: third-postgres
spec:
replicas: 1
template:
metadata:
labels:
name: third-postgres
spec:
containers:
- name: third-postgres
image: postgres
env:
- name: PGDATA
value: /var/lib/postgresql/data/pgdata
- name: POSTGRES_USER
value: third-user
- name: POSTGRES_PASSWORD
value: <password>
- name: POSTGRES_DB
value: third_service_db
ports:
- containerPort: 5432
volumeMounts:
- name: third-postgresdata
mountPath: /var/lib/postgresql/data
volumes:
- name: third-postgresdata
persistentVolumeClaim:
claimName: <second-postgres-data>
Now this Deployment was successfully running but it doesn't create new database third_service_db
May be because second PVC was already exists so it skips the Db create part ?
So is their any way I can use same PVC for my all services and same PVC can have multiple databases. So that when I run kubectl create -f <path-to-thirst-postgres.yaml> it takes name Database configuration from env Variables and create DB in same PVC

Answer 1

You have to create one PVC per Deployment. Once a PVC has been claimed, it must be released before it can be used again.
In the case of AzureDisk, the auto-created volumes can only be mounted by a single node (ReadWriteOnce access mode) so there's one more constraint: each of your Deployments can have at most 1 replica.

Answer 2

Yes you can create as much databas as you want on the same Persistent Volume. You have to change the path value to store different database. See the example below.
apiVersion: v1
kind: PersistentVolume
metadata:
name: ...
namespace: ...
labels:
type: ...
spec:
storageClassName: ...
capacity:
storage: ...
accessModes:
- ...
hostPath:
path: "/mnt/data/DIFFERENT_PATH_FOR_EACH_DATABASE"