Changing the default storage class

Dynamic storage provisioning is a key part of scaling applications. When a storage class is not specified by a PVC, Kubernetes uses the default option. Let's perform the following steps to set our preferred storage class as the default:

1. Let's create a new storage class and define it as the default option at the same time by setting is-default-class to true:

$ cat <<EOF | kubectl apply -f -
kind: StorageClass 
apiVersion: storage.k8s.io/v1 
metadata:
  name: gce-pd-ssd 
  annotations:
    storageclass.kubernetes.io/is-default-class: "true"
provisioner: kubernetes.io/gce-pd 
parameters:
  type: pd-ssd
reclaimPolicy: Retain
allowVolumeExpansion: true
volumeBindingMode: WaitForFirstConsumer
allowedTopologies:
- matchLabelExpressions:
  - key: failure-domain.beta.kubernetes.io/zone
    values:
    - us-central1-a
    - us-central1-b
EOF

2. Having more than one default storage class will cause a problem. You need to remove one. To change the status of an existing storage class after it has been created, first pick a storage class:

$ kubectl get sc
NAME                 PROVISIONER AGE
gce-pd               kubernetes.io/gce-pd 3m52s
gce-pd-ssd (default) kubernetes.io/gce-pd 4s
standard (default)   kubernetes.io/gce-pd 21m

3. Let's set the standard and gce-pd-ssd storage classes as non-default:

$ kubectl patch storageclass standard -p '{"metadata": {"annotations":{"storageclass.beta.kubernetes.io/is-default-class":"false"}}}'
$ kubectl patch storageclass gce-pd-ssd -p '{"metadata": {"annotations":{"storageclass.kubernetes.io/is-default-class":"false"}}}'

4. Let's now define gce-pd as the default storage class again:

$ kubectl patch storageclass gce-pd -p '{"metadata": {"annotations":{"storageclass.kubernetes.io/is-default-class":"true"}}}'

5. Confirm the new default storage class:

$ kubectl get sc
NAME             PROVISIONER          AGE
gce-pd (default) kubernetes.io/gce-pd 8m25s
gce-pd-ssd       kubernetes.io/gce-pd 4m37s
standard         kubernetes.io/gce-pd 25m

Now you have learned how to replace the default storage class with a new storage class. Make sure that there is always one default storage class at a time; otherwise PVCs without a storage class defined that are expecting a default storage class will fail.