Dynamic Storage Provisioning

Dynamic Storage Provisioning

In our environment, we have a cluster with storage provisioner configured. Now, we need to create a PVC object and consume it in a pod.

Let’s create a PVC.

First of all, create a folder for this lab:

mkdir ~/storage ; cd ~/storage

The following description of a persistentVolumeClaim (PVC) uses our storageClass to request 1GB of storage that can be used to populate a volume in a pod. Place it in a file pvc01.yaml:

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: pvc01
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 1G
  storageClassName: <your_sc>

Create the PVC:

kubectl apply -f pvc01.yaml

persistentvolumeclaim/pvc01 created

kubectl get pvc pvc01

The following yaml describes a pod which uses the above PVC to populate a volume, mounts that volume into a container, and periodically writes a message to that storage location so we can see it in action. Place this in a file named pod-pvc.yaml:

apiVersion: v1
kind: Pod
metadata:
  name: hello-pvc-pod
spec:
  volumes:
  - name: volume01
    persistentVolumeClaim:
      claimName: pvc01
  containers:
  - name: hello-container
    image: busybox
    command:
      - sh
      - -c
      - 'while true; do echo "`date` [`hostname`] Hello from the dynamically provisioned \
          Persistent Volume." >> /mnt/store/greet.txt; sleep $(($RANDOM % 5 + 300)); done'
    volumeMounts:
    - mountPath: /mnt/store
      name: volume01

Deploy this pod:

kubectl apply -f pod-pvc.yaml

pod/hello-pvc-pod created

kubectl get pod hello-pvc-pod

NAME                       READY   STATUS    RESTARTS   AGE
hello-pvc-pod              1/1     Running   0          11s

Verify data is being written within the container’s filesystem where we mounted the PV:

kubectl exec hello-pvc-pod  -- cat /mnt/store/greet.txt

Verify that the container is writing to the local persistent volume:

kubectl describe pod hello-pvc-pod

Name:         hello-pvc-pod
Namespace:    default
Priority:     0
Node:         node1/10.10.65.94
....
Volumes:
  volume01:
    Type:       PersistentVolumeClaim (a reference to a PersistentVolumeClaim in the same namespace)
    ClaimName:  pvc01
    ReadOnly:   false
....

Check the details of the PVC:

kubectl get pvc pvc01

NAME                 STATUS   VOLUME    CAPACITY   ACCESS MODES   STORAGECLASS     AGE
pvc01   Bound    pvc-xxx   1G         RWO            local-hostpath   10m

A new persistent volume named pvc-xxx has been dynamically provisioned by our storage class. Let’s look at the details of the persistent volume.

Check the details of the persistent volume:

kubectl describe pv <Volume name from above>

Name:           pvc-xxx
....
Node Affinity:
  Required Terms:
    Term 0:        kubernetes.io/hostname in [node1]
....
Source:
    Type:  LocalVolume (a persistent volume backed by local storage on a node)
    Path:  /data/pvc-xxx

Note in the output the name of the node node1 and actual location within the node’s filesystem /data/pvc-xxx. We can confirm that the greet.txt file is accessible from the source path.

Confirm the greet.txt file location, where nodeX is whichever node you found your pod and volume scheduled on:

cat <PV host path found above>/greet.txt

Fri May 29 20:02:55 UTC 2020 [master01] Hello from the dynamically provisioned Persistent Volume.
Fri May 29 20:02:55 UTC 2020 [master01] Hello from the dynamically provisioned Persistent Volume.

Clean Up

Delete the pod.

kubectl delete pod hello-pod-pvc

Delete the pvc.

kubectl delete pvc pvc01