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Exercise 4: Persistent Volumes

Objective​

Learn how to use PersistentVolumeClaims (PVCs) to provide storage for applications. Understand the difference between ephemeral and persistent storage.

Prerequisites​

Exercise: Create an Application with Persistent Storage​

Step 1: Create a PersistentVolumeClaim​

A PVC requests storage from the cluster. The cluster provisions it using a StorageClass.

YAML Version: Create namespace-pvc.yaml:

apiVersion: v1
kind: Namespace
metadata:
  name: practice-04
---
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: app-storage
  namespace: practice-04
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 1Gi
  storageClassName: longhorn

Apply:

kubectl apply -f namespace-pvc.yaml

Verify:

kubectl get pvc -n practice-04

Wait until the PVC shows Bound status. This means storage has been provisioned.

Step 2: Create a Deployment Using the PVC​

Now let's create a deployment that uses this persistent storage.

YAML Version: Create deployment.yaml:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: storage-app
  namespace: practice-04
spec:
  replicas: 1
  selector:
    matchLabels:
      app: storage-app
  template:
    metadata:
      labels:
        app: storage-app
    spec:
      containers:
        - name: app
          image: busybox
          command: ['/bin/sh']
          args:
            - -c
            - |
              echo "Writing to persistent storage..." > /data/message.txt
              echo "Current time: $(date)" >> /data/message.txt
              echo "Data persisted!" >> /data/message.txt
              cat /data/message.txt
              sleep 3600
          volumeMounts:
            - name: storage
              mountPath: /data
      volumes:
        - name: storage
          persistentVolumeClaim:
            claimName: app-storage

Apply:

kubectl apply -f deployment.yaml

Wait for pod:

kubectl wait --for=condition=ready pod -l app=storage-app -n practice-04 --timeout=60s

Step 3: Verify Data Persistence​

Let's verify that data is being written to persistent storage:

# Check the pod logs
kubectl logs -l app=storage-app -n practice-04

# Check the data in the pod
kubectl exec -it deployment/storage-app -n practice-04 -- cat /data/message.txt

Step 4: Test Data Persistence​

The real test of persistent storage is that data survives pod restarts. Let's test this:

# Delete the pod (it will be recreated by the Deployment)
kubectl delete pod -l app=storage-app -n practice-04

# Wait for new pod
kubectl wait --for=condition=ready pod -l app=storage-app -n practice-04 --timeout=60s

# Check if data still exists
kubectl exec -it deployment/storage-app -n practice-04 -- cat /data/message.txt

The data should still be there! This proves the storage is persistent.

Verification​

Verify persistent storage is working:

# Check PVC status
kubectl get pvc -n practice-04

# Check pod is using the volume
kubectl describe pod -l app=storage-app -n practice-04 | grep -A 5 "Volumes:"

# Verify data persistence after pod restart
kubectl delete pod -l app=storage-app -n practice-04
sleep 10
kubectl exec -it deployment/storage-app -n practice-04 -- ls -la /data

Understanding What Happened​

  • PersistentVolumeClaim (PVC): Requests storage from the cluster
  • StorageClass: Defines how storage is provisioned (we used longhorn)
  • Volume Mount: Makes the storage available inside the container
  • Persistence: Data survives pod restarts and deletions

Cleanup​

Remove all resources:

kubectl delete namespace practice-04

This will also delete the PVC and the underlying volume.

Next Steps​

→ Exercise 5: Longhorn Storage

Additional Practice​

  1. Check available StorageClasses: kubectl get storageclass
  2. Create a PVC with a different size: Change storage: 1Gi to storage: 2Gi
  3. Try mounting the same PVC in multiple pods (hint: ReadWriteOnce means only one pod can mount it)