Day 36: Managing Persistent volumes in your Deplpoyment

• What are persistent volumes in K8s?

  In Kubernetes, a Persistent Volume (PV) is a piece of storage in the cluster that has been provisioned by an administrator. A Persistent Volume Claim (PVC) is a request for storage by a user. The PVC references the PV, and the PV is bound to a specific node.

• What is persistent volume claim?

  A PersistentVolumeClaim (PVC) is a request for storage by a user. It is similar to a Pod. Pods consume node resources and PVCs consume PV resources. Pods can request specific levels of resources (CPU and Memory).

  A user creates, or in the case of dynamic provisioning, has already created, a PersistentVolumeClaim with a specific amount of storage requested and with certain access modes. A control loop in the control plane watches for new PVCs, finds a matching PV (if possible), and binds them together.

  Basically creating only Pv(persistent volume) is not enough you need to claim that volume using PVC.

Task 1:

• Create a Persistent Volume using a file on your node.

    apiVersion: v1
    kind: PersistentVolume
    metadata:
      name: mysql-pv-volume
      namespace: mysql
      labels:
        app: mysql
  
    spec:
      storageClassName: manual
      capacity:
        storage: 2Gi
      accessModes:
        - ReadWriteOnce
      hostPath:
        path: /mnt/volumne
  

  

  Use the command to check persistent volume is created :

  kubectl get pv -n mysql

  

• Create a Persistent Volume Claim that references the Persistent Volume.

    apiVersion: v1
    kind: PersistentVolumeClaim
    metadata:
      name: mysql-pv-claim
      namespace: mysql
    spec:
      storageClassName: manual
      accessModes:
        - ReadWriteOnce
      resources:
        requests:
          storage: 1Gi
  

  

    kubectl get pvc -n mysql
  

  

  You'll see that the status is Bound , it means you've successfully claimed the volume.

• Update your deployment.yml file to include the Persistent Volume Claim. After Applying pv.yml pvc.yml your deployment file look.

    apiVersion: apps/v1
    kind: Deployment
    metadata:
      name: mysql
      namespace: mysql
      labels:
        app: mysql
    spec:
      replicas: 1
      selector:
        matchLabels:
          app: mysql
      template:
        metadata:
          labels:
            app: mysql
        spec:
          containers:
          - name: mysql
            image: mysql:8
            ports:
            - containerPort: 3306
            env:
            - name: MYSQL_ROOT_PASSWORD
              valueFrom:
                secretKeyRef:
                  name: mysql-secret
                  key: password
            - name: MYSQL_DATABASE
              valueFrom:
                configMapKeyRef:
                  name: mysql-config
                  key: MYSQL_DB
            volumeMounts:
            - name: mysql-persistent-storage
              mountPath: /var/lib/mysql
          volumes:
          - name: mysql-persistent-storage
            persistentVolumeClaim:
              claimName: mysql-pv-claim
  

• Apply the updated deployment using the command: kubectl apply -f deployment.yml

  

Task 2:

• Connect to a Pod in your Deployment using the command :

    kubectl exec -it -- /bin/bash
  

Conclusion:

Persistent Volumes and Persistent Volume Claims are the cornerstones of managing stateful applications in a Kubernetes environment. By understanding how to set up, utilize, and manage these resources, you can ensure that your applications remain stateful, even in the transient world of Kubernetes.