K8s references: K8s Persistent Volume

April 02, 2022

Created by Ranjith Vijayan on Apr 04, 2022

This post is created for my own reference of k8s resources as part of learning

A PersistentVolume (PV) is a piece of storage in the cluster that has been provisioned by an administrator or dynamically provisioned using Storage Classes.

Kubernetes provides 2 API resources namely PersistentVolume and PersistentVolumeClaim to achieve this

PersistentVolume types are implemented as plugins. Kubernetes currently supports various plugins including cloud service providers specific (AWS EBS,Azure Disk etc), NFS, HostPath etc.

In this chapter we will document a simple HostPath type of Persistent volume. HostPath Volumes are not recommended for production. This is only for Testing. This works only when the same host-path is available on every worker nodes of K8s.

In this example we assume that you already have NFS mount with same path (/scratch/share/kbz-file-share) available on every worker node (so that regardless of which node the pod will be scheduled the file can be shared using NFS mount point) To setup NFS and mount them to the required VMs refer to NFS Server documentation.

Create PV

pv.yaml

apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv-test
  labels:
    type: local
spec:
  storageClassName: manual
  capacity:
    storage: 10Gi
  accessModes:
    - ReadWriteOnce
  hostPath:
    path: "/scratch/share/kbz-file-share"

Apply

        kubectl apply -f pv.yaml

Check - kubectl get pv

        ¿ kubectl get pv
        NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS      CLAIM                   STORAGECLASS   REASON   AGE
        pv-test                                    10Gi       RWO            Retain           Bound       pv-test/task-pv-claim   manual                  114m

Create Persistence Volume Claim (PVC)

    pvc.yaml ``` yaml apiVersion: v1 kind: PersistentVolumeClaim metadata:   name: task-pv-claim   namespace: pv-test spec:   storageClassName: manual   accessModes:
- ReadWriteOnce   resources:
requests:
  storage: 3Gi ```

Check

        ¿ kubectl get pvc -n pv-test
        NAME            STATUS   VOLUME    CAPACITY   ACCESS MODES   STORAGECLASS   AGE
        task-pv-claim   Bound    pv-test   10Gi       RWO            manual         115m

Example Podcheck

pod.yaml

apiVersion: v1
kind: Pod
metadata:
  name: task-pv-pod
  namespace: pv-test
spec:
  volumes:
    - name: task-pv-storage
      persistentVolumeClaim:
        claimName: task-pv-claim
  containers:
    - name: task-pv-container
      env:
      - name: OB_POD_NAME
        valueFrom:
          fieldRef:
            apiVersion: v1
            fieldPath: metadata.name
      - name: OB_NAMESPACE_NAME
        valueFrom:
          fieldRef:
            apiVersion: v1
            fieldPath: metadata.namespace
      - name: OB_ENV_NAME
        value: sit
      image: fsgbu-mum-128.snbomprshared1.gbucdsint02bom.oraclevcn.com:5000/utils/nginx:latest
      ports:
        - containerPort: 80
          name: "http-server"
      volumeMounts:
        - mountPath: "/u01/oracle/logs"
          name: task-pv-storage
          subPathExpr: logs/$(OB_ENV_NAME)/$(OB_NAMESPACE_NAME)/$(OB_POD_NAME)

Note: a subPathExpr is used in this example to mount a sub-directory within the main volume directory. the sub-path will be automatically created if its not present.

Apply

kubectl apply -f pod.yaml
pod/task-pv-pod created

Check

kubectl get po -n pv-test   
NAME          READY   STATUS    RESTARTS   AGE
task-pv-pod   1/1     Running   0          86s

Test the directory is mounted and we are able to write file

kubectl exec -it -n pv-test task-pv-pod -- sh
# cd /u01/oracle/logs
# ls
# touch abcd.txt
# exit

check the file is available on the physical host

        ls /scratch/share/kbz-file-share/logs/sit/pv-test/task-pv-pod/        
        abcd.txt