How to update a storageClassName in a statefulset? - kubernetes

Question

I am new to k8's and trying to update storageClassName in a StatefulSet.(from default to default-t1 only change in the yaml)
I tried running kubectl apply -f test.yaml
The only difference between 1st and 2nd Yaml(one using to apply update) is storageClassName: default-t1 instead of default
apiVersion: apps/v1
kind: StatefulSet
metadata:
name: web
spec:
serviceName: "nginx"
podManagementPolicy: "Parallel"
replicas: 2
selector:
matchLabels:
app: nginx
template:
metadata:
labels:
app: nginx
spec:
containers:
- name: nginx
image: k8s.gcr.io/nginx-slim:0.8
ports:
- containerPort: 80
name: web
volumeMounts:
- name: www
mountPath: /usr/share/nginx/html
volumeClaimTemplates:
- metadata:
name: www
spec:
accessModes: [ "ReadWriteOnce" ]
storageClassName: default
resources:
requests:
storage: 1Gi
Every-time I try to update it I get The StatefulSet "web" is invalid: spec: Forbidden: updates to statefulset spec for fields other than 'replicas', 'template', and 'updateStrategy' are forbidden
What am I missing or what steps should I take to do this?

Answer 1

There's no easy way as far as I know but it's possible.
Save your current StatefulSet configuration to yaml file:
kubectl get statefulset some-statefulset -o yaml > statefulset.yaml
Change storageClassName in volumeClaimTemplate section of StatefulSet configuration saved in yaml file
Delete StatefulSet without removing pods using:
kubectl delete statefulset some-statefulset --cascade=orphan
Recreate StatefulSet with changed StorageClass:
kubectl apply -f statefulset.yaml
For each Pod in StatefulSet, first delete its PVC (it will get stuck in terminating state until you delete the pod) and then delete the Pod itself
After deleting each Pod, StatefulSet will recreate a Pod (and since there is no PVC) also a new PVC for that Pod using changed StorageClass defined in StatefulSet.

Answer 2

apiVersion: apps/v1
kind: StatefulSet
metadata:
name: web
spec:
serviceName: "nginx"
podManagementPolicy: "Parallel"
replicas: 2
selector:
matchLabels:
app: nginx
template:
metadata:
labels:
app: nginx
spec:
containers:
- name: nginx
image: k8s.gcr.io/nginx-slim:0.8
ports:
- containerPort: 80
name: web
volumeMounts:
- name: www
mountPath: /usr/share/nginx/html
volumeClaimTemplates:
- metadata:
name: www
spec:
accessModes: [ "ReadWriteOnce" ]
storageClassName: <storage class name>
resources:
requests:
storage: 1Gi
in the above file add storage class and you can apply it like.
kubectl apply -f .yaml

Answer 3

First line of StatefulSet shoud define an "apiVersion", you can see example here statefulset. Please add it in first line:
apiVersion: apps/v1
Could you show me output of your 'www' PVC file?
kubectl get pvc www -o yaml
In PVC you have field "storageClassName", which should be set on your StorageClass you want to use, so in your case it would be:
storageClassName: default-t1