In Chapter 2, Walking through Kubernetes Concepts, we learned how to declare PersistentVolume and PersistentVolumeClaim. With dynamic provisioning, you can define a set of StorageClass with different physical storage backends and use them in PersistentVolume or PersistentVolumeClaim. Let's see how it works.

To check the current default StorageClass, use kubectl get storageclasses command:

# kubectl get storageclasses
NAME                 PROVISIONER            AGE
standard (default)   kubernetes.io/gce-pd   1h

We can see we have a default storage class named standard and its provisioner is GCE PD.

Let's create a PersistentVolumeClaim request and use the standard StorageClass as the backend:

# cat gke-pvc.yaml
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
    name: pvc-example-pv
spec:
  storageClassName: standard
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 10Gi

// create resources
# kubectl create -f gke-pvc.yaml
persistentvolumeclaim "pvc-example-pv" created

storageClassName is the place to put the name of the StorageClass. If you put in something that doesn't exist, PVC will not be created, since there is no proper mapped StorageClass to use:

// check pvc status
# kubectl get pvc
NAME              STATUS    VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGE
pvc-example-pv    Bound     pvc-1491b08e-1cfc-11e8-8589-42010a800360   10Gi       RWO            standard       12m

// describe the details of created PVC
# kubectl describe pvc pvc-example-pv
Name:          pvc-example-pv
Namespace:     default
StorageClass:  standard
Status:        Bound
Volume:        pvc-1491b08e-1cfc-11e8-8589-42010a800360
Labels:        <none>
Annotations:   pv.kubernetes.io/bind-completed=yes
               pv.kubernetes.io/bound-by-controller=yes
               volume.beta.kubernetes.io/storage-provisioner=kubernetes.io/gce-pd
Finalizers:    []
Capacity:      10Gi
Access Modes:  RWO
Events:
  Type    Reason                 Age   From                         Message
  ----    ------                 ----  ----                         -------
  Normal  ProvisioningSucceeded  12m   persistentvolume-controller  Successfully provisioned volume pvc-1491b08e-1cfc-11e8-8589-42010a800360 using kubernetes.io/gce-pd

We can see volume pvc-1491b08e-1cfc-11e8-8589-42010a800360 has been created and bounded. If we list GCP disks, we'll find there was a Persistent Disk created; the suffix of the disk name indicates the volume name in Kubernetes. That's the magic of dynamic volume provisioning:

# gcloud compute disks list
NAME                                                             ZONE           SIZE_GB  TYPE         STATUS
gke-my-k8s-cluster-5ef-pvc-1491b08e-1cfc-11e8-8589-42010a800360  us-central1-a  10       pd-standard  READY