luc.run

Persist the VotingApp’s databases

By default, k3s comes with the default StorageClass named local-path which can be verified using the following command.

$ kubectl get storageclass
NAME                   PROVISIONER             RECLAIMPOLICY   VOLUMEBINDINGMODE      ALLOWVOLUMEEXPANSION   AGE
local-path (default)   rancher.io/local-path   Delete          WaitForFirstConsumer   false                  1h4m

In a file named pvc-redis.yaml, define the specification for a PersistentVolumeClaim with the following characteristics:

name: redis
ReadWriteOnce mode
request for 1G storage

Then modify the redis Deployment specification by adding a volume based on this PersistentVolumeClaim, and use the volumeMounts instruction to ensure that the associated PersistentVolume is mounted in the /data directory of the redis container.

In a file named pvc-db.yaml containing the specification for a PersistentVolumeClaim with the following characteristics:
- name: db
- ReadWriteOnce mode
- request for 1G of storage
Then modify the db Deployment specification by adding a volume based on this PersistentVolumeClaim, and use the volumeMounts instruction to ensure that the associated PersistentVolume is mounted in the /var/lib/postgresql/data directory of the postgres container.
Deploy the application defined in these specifications and verify that it is working correctly.
List the PersistentVolumeClaim resources. What do you observe?
Delete the application.

Solution

The specification to define the PersistentVolumeClaim named redis:

pvc-redis.yaml

apiVersion: v1
kind: PersistentVolumeClaim
metadata: 
  name: redis
spec: 
  accessModes:
    - ReadWriteOnce
  resources:
    requests: 
      storage: 1Gi

The redis Deployment is modified as follows:

deploy-redis.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: redis
  name: redis
spec:
  replicas: 1
  selector:
    matchLabels:
      app: redis
  template:
    metadata:
      labels:
        app: redis
    spec:
      containers:
        - image: redis:7.0.8-alpine3.17
          name: redis
          volumeMounts:
          - name: data
            mountPath: /data
      volumes:
      - name: data
        persistentVolumeClaim:
          claimName: redis

The specification to define the PersistentVolumeClaim named db:

pvc-db.yaml

apiVersion: v1
kind: PersistentVolumeClaim
metadata: 
  name: db
spec: 
  accessModes:
    - ReadWriteOnce
  resources:
    requests: 
      storage: 1Gi

The db Deployment is modified as follows:

deploy-db.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: db
  name: db
spec:
  replicas: 1
  selector:
    matchLabels:
      app: db
  template:
    metadata:
      labels:
        app: db
    spec:
      containers:
        - image: postgres:15.1-alpine3.17
          name: postgres
          env:
            - name: POSTGRES_PASSWORD
              valueFrom:
                secretKeyRef:
                  name: db
                  key: password
          volumeMounts:
          - name: data
            mountPath: /var/lib/postgresql/data
          ports:
            - containerPort: 5432
              name: postgres
      volumes:
      - name: data
        persistentVolumeClaim: 
          claimName: db

Deploy the application using the following command from the manifests directory:

kubectl apply -f .

Using the IP address of one of the cluster nodes, you can access the vote and result interfaces via ports 31000 and 31001 respectively.

You can list the PersistentVolumeClaim resources and observe that a PersistentVolume has been created for each of the 2 PVCs.

List of PersistentVolumeClaims:

$ kubectl get pvc
NAME                          STATUS   VOLUME                                     CAPACITY  ACCESS MODES   STORAGECLASS   AGE
persistentvolumeclaim/redis   Bound    pvc-789e3c5c-4402-4b96-b09d-ee441e8ade1d   1Gi       RWO            local-path     39s
persistentvolumeclaim/db      Bound    pvc-75b9a32c-eab5-4452-a9b8-12d41dd74e7a   1Gi       RWO            local-path     39s

List of PersistentVolumes:

$ kubectl get pv
NAME                                                        CAPACITY  ACCESS MODES   RECLAIM POLICY   STATUS   CLAIM           STORAGECLASS   REASON   AGE
persistentvolume/pvc-789e3c5c-4402-4b96-b09d-ee441e8ade1d   1Gi       RWO            Delete           Bound    default/redis   local-path              32s
persistentvolume/pvc-75b9a32c-eab5-4452-a9b8-12d41dd74e7a   1Gi       RWO            Delete           Bound    default/db      local-path              32s

Delete the application using the following command from the manifests directory:

kubectl delete -f .