Kubernetes - Persistent Volume Claims 🚩

Description 👀

Persistent Volume Claims, otherwise known as PVC, and Persistent Volumes are two separate Kubernetes resources. PVC are a way to dynamically provision from a persistent volume based on the request and properties set on the volume such as size, access mode, storage class, etc. PVC are also used to bind persistent volumes to pods and containers in order to persist data. PVC are also used to reclaim persistent volumes when they are no longer needed. Every PVC is bound to a single persistent volume. There is a 1:1 relationship between PVC and persistent volumes.

Basic Commands 📝

• get pvc

    kubectl get pvc
  

• delete pvc

    kubectl delete pvc <pvc-name>
  

  • but what happens to the underlying persistent volume 🤔

    • by default the persistent volume reclaim policy is set to retain, but can be changed to delete or recycle.

            # persistent volume reclaim policy can be set to delete, retain, or recycle
            # this is placed in the pv spec section
            persistentVolumeReclaimPolicy: Retain
      

Examples 🧩

• persistent volume claim definition

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

  • similar to persistent volumes, accessMode can be ReadWriteOnce, ReadOnlyMany, or ReadWriteMany

• use persistent volume claim in a pod definition

    apiVersion: v1
    kind: Pod
    metadata:
        name: mypod
    spec:
        containers:
          - name: myfrontend
            image: nginx
            volumeMounts:
              - mountPath: "/var/www/html"
                name: mypd
        volumes:
          - name: mypd
            persistentVolumeClaim:
                claimName: myclaim
  

  • persistent volume claim is defined in the volumes section of the pod definition
  • persistent volume claim is mounted to the pod in the volumeMounts section of the pod definition

• pvc for use with examples in pv and volumes section

    apiVersion: v1
    kind: PersistentVolumeClaim
    metadata:
        name: claim-log-1
    spec:
        accessModes:
          - ReadWriteOnce
        resources:
            requests:
                storage: 50Mi
  

  • update pod from initial example to use pvc

    apiVersion: v1
    kind: Pod
    metadata:
        name: webapp
    spec:
        containers:
            - name: event-simulator
            image: kodekloud/event-simulator
            env:
              - name: LOG_HANDLERS
                value: file
            volumeMounts:
              - mountPath: /log
                name: log-volume
        volumes:
          - name: log-volume
            persistentVolumeClaim:
                claimName: claim-log-1
    

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