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Exercise 5: Longhorn Storage

Objective​

Learn how to use Longhorn for distributed, replicated storage in your K3s cluster. Understand Longhorn-specific features and volume management.

Prerequisites​

Exercise: Use Longhorn for Distributed Storage​

Step 1: Verify Longhorn Installation​

First, let's make sure Longhorn is running:

# Check Longhorn pods
kubectl get pods -n longhorn-system

# Check StorageClass
kubectl get storageclass longhorn

If Longhorn isn't installed, you'll need to install it first (see Longhorn Setup documentation).

Step 2: Create a PVC Using Longhorn​

Longhorn provides the longhorn StorageClass. Let's create a PVC that uses it explicitly.

YAML Version: Create longhorn-pvc.yaml:

apiVersion: v1
kind: Namespace
metadata:
  name: practice-05
---
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: longhorn-volume
  namespace: practice-05
spec:
  accessModes:
    - ReadWriteOnce
  storageClassName: longhorn
  resources:
    requests:
      storage: 2Gi

Apply:

kubectl apply -f longhorn-pvc.yaml

Verify:

kubectl get pvc -n practice-05

Wait for Bound status.

Step 3: Check Longhorn Volume​

Longhorn creates a volume resource you can inspect:

# List Longhorn volumes
kubectl get volumes -n longhorn-system

# Describe the volume (replace with your volume name)
kubectl get volumes -n longhorn-system -o name | head -1 | xargs kubectl describe -n longhorn-system

Step 4: Create a Stateful Application​

Let's create a database-like application that benefits from persistent storage.

YAML Version: Create stateful-app.yaml:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: database-app
  namespace: practice-05
spec:
  replicas: 1
  selector:
    matchLabels:
      app: database-app
  template:
    metadata:
      labels:
        app: database-app
    spec:
      containers:
        - name: db
          image: postgres:15-alpine
          env:
            - name: POSTGRES_DB
              value: myapp
            - name: POSTGRES_USER
              value: admin
            - name: POSTGRES_PASSWORD
              value: password123
          ports:
            - containerPort: 5432
          volumeMounts:
            - name: data
              mountPath: /var/lib/postgresql/data
      volumes:
        - name: data
          persistentVolumeClaim:
            claimName: longhorn-volume

Apply:

kubectl apply -f stateful-app.yaml

Wait for pod:

kubectl wait --for=condition=ready pod -l app=database-app -n practice-05 --timeout=120s

Step 5: Test Data Persistence​

Let's create some data and verify it persists:

# Create a test database
kubectl exec -it deployment/database-app -n practice-05 -- \
  psql -U admin -d myapp -c "CREATE TABLE test (id SERIAL, data TEXT);"

# Insert some data
kubectl exec -it deployment/database-app -n practice-05 -- \
  psql -U admin -d myapp -c "INSERT INTO test (data) VALUES ('This data should persist');"

# Verify data exists
kubectl exec -it deployment/database-app -n practice-05 -- \
  psql -U admin -d myapp -c "SELECT * FROM test;"

Step 6: Test Longhorn Replication​

Longhorn replicates data across nodes. Let's verify the volume is replicated:

# Check volume replication status in Longhorn
kubectl get volumes -n longhorn-system

# Check Longhorn UI (if accessible)
# kubectl port-forward -n longhorn-system svc/longhorn-frontend 8080:80

Verification​

Verify Longhorn storage is working correctly:

# Check PVC is bound
kubectl get pvc -n practice-05

# Check Longhorn volume exists
kubectl get volumes -n longhorn-system

# Verify data persists after pod restart
kubectl delete pod -l app=database-app -n practice-05
sleep 15
kubectl exec -it deployment/database-app -n practice-05 -- \
  psql -U admin -d myapp -c "SELECT * FROM test;"

Understanding What Happened​

  • Longhorn StorageClass: Provides distributed, replicated storage
  • Volume Replication: Longhorn replicates data across multiple nodes for redundancy
  • Persistent Storage: Data survives pod restarts and node failures
  • Stateful Applications: Perfect for databases and applications that need persistent data

Cleanup​

Remove all resources:

kubectl delete namespace practice-05

This will delete the PVC and the Longhorn volume.

Next Steps​

→ Exercise 6: Services and Networking

Additional Practice​

  1. Check Longhorn volume details: kubectl get volumes -n longhorn-system -o yaml
  2. Create multiple PVCs and see how Longhorn manages them
  3. Check Longhorn UI to see volume replication status (if you have access to it)