Static Provisioning

Introduction

In the 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 perspective the volume is deleted.

The PersistentVolumes API solves this problem where PVs have a lifecycle independent of the Pods and are not dependant on a Pod to persist. PVs are units of storage provisioned in advance, they are Kubernetes objects backed by vSphere storage. PVs are created and deleted using kubectl commands.

In order to use these PVs the user needs to create PersistentVolumeClaims which is simply a request for some storage. A PVC must specify the access mode and storage capacity, once a PVC is created a PV is automatically bound to this claim. Kubernetes will bind a PV to PVC based on the access mode and storage capacity. The PVC can also mention volume name, selectors and volume class for a better match.

This design of PV to PVC mappings not only abstracts storage provisioning and consumption but also ensures security through access control.

Manually provisioning volumes

Here is an example of how to use PVs and PVCs to add persistent storage to your Pods.

Create vSphere VMDK

Via govc (preferred)

Requests a 2GB VMDK be created on the datastore1 datastore in a folder called volumes with a name of myDisk.vmdk:

govc datastore.disk.create -ds datastore1 -size 2G volumes/myDisk.vmdk

Via ESXi CLI

SSH into an ESXi host as root and use following command to create a 2GB VMDK (this assumes your vSphere datastore is called datastore1 and you want to create the VMDK in the folder volumes):

vmkfstools -c 2G /vmfs/volumes/datastore1/volumes/myDisk.vmdk

Create a PersistentVolume

Define the PersistentVolume

As you can see below, we call the PV “pv0001” and pass in the VMDK path to the volumePath parameter.

$ cat 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 of vCenter. If the datastore is the member of a Datastore Cluster or located in subfolder, then the folder path needs to be provided in the volumePath as shown below.

vsphereVolume:
  volumePath: "[DatastoreCluster/datastore1] volumes/myDisk"

Import the PersistentVolume

Import the PersistentVolume definition we created above into our Kubernetes cluster using kubectl:

kubectl create -f vsphere-volume-pv.yaml

Verify the PersistentVolume

Verify the PV we imported above was created correctly:

$ 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 a PersistentVolumeClaim

Define the PersistentVolumeClaim

Create a PVC to consume the PV created above - in this example the PVC simply requests 2GB of storage:

$ cat vsphere-volume-pvc.yaml

kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: pvc0001
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 2Gi

Import the PersistentVolumeClaim

Import the PVC definition from above into our Kubernetes cluster:

kubectl create -f vsphere-volume-pvc.yaml

Verify the PersistentVolumeClaim

Ensure the PVC we created has been assigned a PV - the Status should show Bound and the Volume field should show the PV name from above, in this case pv0001.

$ kubectl describe pvc pvc0001
Name:		pvc0001
Namespace:	default
Status:		Bound
Volume:		pv0001
Labels:		<none>
Capacity:	2Gi
Access Modes:	RWO
No events.

Create a Pod using the PVC

Define the Pod

Create a simple Pod the consumes the PVC created above by name pvc0001:

$ cat vsphere-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

Import the Pod

Import the Pod definition from above into our Kubernetes cluster:

kubectl create -f vsphere-volume-pvcpod.yaml

Verify the Pod

Make sure the PV was bound to the pod correctly by ensuring the STATUS is set to Running:

$ kubectl get pod pvpod
NAME      READY     STATUS    RESTARTS   AGE
pvpod       1/1     Running   0          48m

You have successfully manually provisioned a Kubernetes volume on vSphere.