Day 36- 90DaysOfDevOps

Hey Learners! Welcome back. In the previous task, we learned about ConfigMap and Secret to store our non-confidential as well as confidential data. In this challenge, we'll dig in depth with the concept of Persistent Volume. Let's start...

What are Persistent Volumes in K8s?

Problem:- As we know if the container (Pod) gets down then it will be restarted but the data present in the container/pod will be lost. Using Hostpath we can eliminate this data loss but in the K8s cluster Pod might get restarted on another worker so in this case Hostpath will not be accessible.

Solution:- To avoid data loss in the K8s cluster we'll use Persistent Volumes.

A Persistent Volume(PV) is a cluster-wide resource that you can use to store data in a way that persists beyond the lifetime of the Pod. The PV is not backed by locally attached storage on a work node but by a networked storage system such as EBS or NFS or a Distributed File System like Ceph.

Persistent Volume Claim(PVC):-

To Use PV you need to claim it first, using a persistent volume Claim.

The PVC request a PV with your desired specification(Size, Access, Speed, etc.) from K8s and once a suitable PV is found it is bound to be PVC.

After a successful bound to a Pod, you can mount it as a volume.

Task 1- Add a Persistent Volume to your Deployment todo-app.

1. Create a PV using a file on the node. vim todo-app-PV.yml and create PV using kubectl apply -f todo-app-PV command.

    kind: PersistentVolume
    metadata:
      name: todo-app-pv
    spec:
      capacity:
        storage: 200Mi
      accessModes:
        - ReadWriteOnce
      persistentVolumeReclaimPolicy: Retain
      hostPath:
        path: "/tmp/pv"
   

   

2. Now create PVC that refers to the PV. vim todo-app-PVC.yml and create PVC using kubectl apply -f todo-app-PVC.yml command

    apiVersion: v1
    kind: PersistentVolumeClaim
    metadata:
      name: todo-app-pvc
    spec:
      accessModes:
        - ReadWriteOnce
      resources:
        requests:
          storage: 100Mi
   

   

3. Update the deployment.yml file as shown vim deployment.yml and apply the changes using kubectl apply -f deployment.yml command.

    apiVersion: apps/v1
    kind: Deployment
    metadata:
      name: todo
      namespace: node-app
      labels:
        app: todo-app
    spec:
      replicas: 2
      selector:
        matchLabels:
          app: todo-app
      template:
        metadata:
          namespace: node-app 
          labels:
            app: todo-app
        spec:
          containers:
            - name: todo-container
              image: amitvpawar/node-app:v2
              ports:
                - containerPort: 5000
              volumeMounts:
                - name: todo-app-data
                  mountPath: /app
          volumes:
            - name: todo-app-data
              persistentVolumeClaim:
                claimName: todo-app-pvc
   

   

4. To list PVs and Pod use kubectl get pods -n <namespace-if-any> and kubectl get pv

   

Task 2- Accessing data in the Persistent Volume.

1. First, connect/execute one of the running Pods using kubectl exec -it <pod-name> -- /bin/bas. Add some files.

2. Delete the pod in which we made changes.

3. Check whether the new pod have created files or not.

Thank you so much for taking the time to read till the end! Hope you found this blog informative.

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Happy Learning!