In case of Kubernetes Volumes, once the Pod is deleted the specification of the volume in the Pod is also lost. Even though VMDK file persists but from Kubernetes’s perspective the volume is deleted.
Persistent Volumes API resource solves this problem where PVs have lifecycle independent of the Pods and not created when Pod is spawned. PVs are units of storage provisioned in advance, they are Kubernetes objects backed by vSphere storage. PVs are created, deleted using kubectl commands.
In order to use these PVs user needs to create PersistentVolumeClaims which is nothing but a request for PVs. A claim must specify the access mode and storage capacity, once a claim is created PV is automatically bound to this claim. Kubernetes will bind a PV to PVC based on access mode and storage capacity but claim can also mention volume name, selectors and volume class for a better match. This design of PV-PVCs not only abstract storage provisioning and consumption but also ensures security through access control.
All the example yamls can be found here unless otherwise specified. Please download these examples.
Here is an example of how to use PV and PVC to add persistent storage to your Pods.
First ssh into ESX and then use following command to create vmdk,
vmkfstools -c 2G /vmfs/volumes/datastore1/volumes/myDisk.vmdk
Create Persistent Volume
#vsphere-volume-pv.yaml apiVersion: v1 kind: PersistentVolume metadata: name: pv0001 spec: capacity: storage: 2Gi accessModes: - ReadWriteOnce persistentVolumeReclaimPolicy: Retain vsphereVolume: volumePath: "[datastore1] volumes/myDisk" fsType: ext4
In the above example, datastore1 is located in the root folder. If datastore is the member of Datastore Cluster or located in sub folder, then folder path needs to be provided in the VolumePath as mentioned below.
vsphereVolume: VolumePath: "[DatastoreCluster/datastore1] volumes/myDisk"
Create the persistent volume
$ kubectl create -f vsphere-volume-pv.yaml
Verify persistent volume is created
$ kubectl describe pv pv0001 Name: pv0001 Labels: <none> Status: Available Claim: Reclaim Policy: Retain Access Modes: RWO Capacity: 2Gi Message: Source: Type: vSphereVolume (a Persistent Disk resource in vSphere) VolumePath: [datastore1] volumes/myDisk FSType: ext4 No events.
Create Persistent Volume Claim
#vsphere-volume-pvc.yaml kind: PersistentVolumeClaim apiVersion: v1 metadata: name: pvc0001 spec: accessModes: - ReadWriteOnce resources: requests: storage: 2Gi
Create the persistent volume claim
$ kubectl create -f vsphere-volume-pvc.yaml
Verify persistent volume claim is created
$ kubectl describe pvc pvc0001 Name: pvc0001 Namespace: default Status: Bound Volume: pv0001 Labels: <none> Capacity: 2Gi Access Modes: RWO No events.
Create Pod which uses Persistent Volume Claim
#vpshere-volume-pvcpod.yaml apiVersion: v1 kind: Pod metadata: name: pvpod spec: containers: - name: test-container image: gcr.io/google_containers/test-webserver volumeMounts: - name: test-volume mountPath: /test-vmdk volumes: - name: test-volume persistentVolumeClaim: claimName: pvc0001
Create the pod
$ kubectl create -f vsphere-volume-pvcpod.yaml
Verify pod is created
$ kubectl get pod pvpod NAME READY STATUS RESTARTS AGE pvpod 1/1 Running 0 48m