Handle immutable fields with a ValidatingWebhook

[Skaronator]

I'm just in the evaluation process of a memcached / redis operator and dragonfly seems to be a valid option. While initial testing the operator I noticed that it doesn't handle some changes correctly, resulting in a "broken" deployment.

For example adding snapshot to a existing PVC breaks the Dragonfly resource.

Deploy this:

apiVersion: dragonflydb.io/v1alpha1
kind: Dragonfly
metadata:
  name: dragonfly-sample
spec:
  replicas: 3
  resources:
    requests:
      cpu: 100m
      memory: 256Mi

Then add a PVC and you can successfully apply this resource, resulting in many errors in the operator.

apiVersion: dragonflydb.io/v1alpha1
kind: Dragonfly
metadata:
  name: dragonfly-sample
spec:
  replicas: 3
  resources:
    requests:
      cpu: 100m
      memory: 256Mi
  snapshot:
    cron: "* * * * *"
    persistentVolumeClaimSpec:
      storageClassName: efs
      accessModes:
        - ReadWriteOnce
      resources:
        requests:
          storage: 2Gi

Other Operators handle this way better with an ValidatingWebhookConfiguration. They throw an error and saying that the snapshot field is immutable and cannot be changed without recreating that resource.

[Pothulapati]

Other Operators handle this way better with an ValidatingWebhookConfiguration. They throw an error and saying that the snapshot field is immutable and cannot be changed without recreating that resource.

Thanks for the report.We can do the same I think.