What are Persistent Volumes in Kubernetes?

In Kubernetes, Persistent Volumes (PV) provide a way to store data beyond the lifecycle of individual pods. They’re independent storage units in the cluster, provisioned by administrators.

On the other hand, a Persistent Volume Claim (PVC) is how applications (or users) request storage resources from the PVs. By binding a PVC to a PV, your pods can access data stored across restarts and rescheduling, ensuring data persistence.

📖 For more details, check out the official documentation on Persistent Volumes.

Today’s Tasks:

Task 1: Add a Persistent Volume to Your Deployment Todo App

In this task, we will add a Persistent Volume to your todo-app Kubernetes deployment. Persistent storage is crucial for any app that needs to retain data, such as databases or file storage.

Steps:

1. Create a Persistent Volume (PV) using a YAML file on your node.

   pv.yml:

    apiVersion: v1
    kind: PersistentVolume
    metadata:
      name: pv-todo-app
    spec:
      capacity:
        storage: 1Gi
      accessModes:
        - ReadWriteOnce
      persistentVolumeReclaimPolicy: Retain
      hostPath:
        path: "/tmp/data"
   

2. Create a Persistent Volume Claim (PVC) that requests storage from the PV.

   pvc.yml:

    apiVersion: v1
    kind: PersistentVolumeClaim
    metadata:
      name: pvc-todo-app
    spec:
      accessModes:
        - ReadWriteOnce
      resources:
        requests:
          storage: 500Mi
   

3. Update the deployment file to use the Persistent Volume Claim.

   deployment.yml:

    apiVersion: apps/v1
    kind: Deployment
    metadata:
      name: todo-app-deployment
    spec:
      replicas: 1
      selector:
        matchLabels:
          app: todo-app
      template:
        metadata:
          labels:
            app: todo-app
        spec:
          containers:
            - name: todo-app
              image: rishikeshops/todo-app
              ports:
                - containerPort: 8000
              volumeMounts:
                - name: todo-app-data
                  mountPath: /app
          volumes:
            - name: todo-app-data
              persistentVolumeClaim:
                claimName: pvc-todo-app
   

4. Apply the Persistent Volume and Claim:

    kubectl apply -f pv.yml
    kubectl apply -f pvc.yml
    kubectl apply -f deployment.yml
   

5. Verify the addition of Persistent Volume:

    kubectl get pv
    kubectl get pvc
    kubectl get pods
   

Note: Remember to apply each YAML file separately before applying the deployment changes.

Task 2: Accessing Data in the Persistent Volume

Once the Persistent Volume is added to your app, it’s time to ensure that the data can be accessed from within the pod.

Steps:

1. Connect to a Pod in your deployment using this command:

    kubectl exec -it <pod-name> -- /bin/bash
   

2. Verify Access to the data stored in the Persistent Volume from within the Pod:

   • Navigate to the mounted path (/app) inside the container.

   • Check if the data is present and accessible.

Need help understanding how Persistent Volumes work? Check out this helpful video tutorial.

🎉 Conclusion

Today, we explored how to use Persistent Volumes to ensure that your Kubernetes applications can store data permanently, even across pod restarts. This is a crucial feature for any stateful application. With the addition of PVs and PVCs, your app can now manage data efficiently.

What you learned:

• How to create a Persistent Volume (PV) and Persistent Volume Claim (PVC).

• How to integrate them into your Kubernetes deployments.

• How to verify and access data stored in PVs from your app's pod.

Keep building your Kubernetes skills, and don’t forget to share your progress on LinkedIn with #90DaysOfDevOps! 🚀