Support to patch annotation (like minReplica/maxReplica) in revision, and apply the modification to all it's sub resources.

[lvjing2]

In what area(s)?

/area autoscale

/kind good-first-issue

/kind spec

Describe the feature

Current, if I modify the minReplica and maxReplica in revision, the reconcile didn't apply such modification to all it's sub resources.

How to reproduce

1. create a ksvc
2. patch the label and annotations for the revision
3. check the label and annotations for the revision, it had been patched
4. check the label and annotations for it's sub resource, it had not been modified.

[yanweiguo]

Revision is immutable. We don't expect patching to a revision will make a change.

Instead, we should not allow users to modify the revision. IIUC, currently making fields of K8S CRD resource immutable is still a feature request. @mattmoor Is it possible to reconcile labels and annotations of a revision to its first status?

[markusthoemmes]

FWIW, IIRC these can be corrected "in-place" by adjusting the PodAutoscaler entity directly.

[yanweiguo]

FWIW, IIRC these can be corrected "in-place" by adjusting the PodAutoscaler entity directly.

Yeah, we allow changing the annotations of the PodAutoscaler and expect a change: https://github.com/knative/serving/tree/master/docs/scaling

[markusthoemmes]

Is this still valid @yanweiguo @lvjing2? Seems like we want to either rephrase the feature or close as "won't fix"?

[yanweiguo]

Actually I'm thinking about what the intended behavior should be.

Current behavior:

Labels are populated from revision to PA. Changes of PA labels have effect while changes of revision labels do not.

Questions

1. When we talk about a revision is immutable, which part of revision is immutable? At least status can change.
2. Shall we populate labels back from PA to revision after PA changed? Having inconsistent labels for autoscaling can cause confusion.
3. If we allow changing PA labels AND populating labels back to revision which resulting in revision labels change, why not allow changing revision labels directly?

[markusthoemmes]

Annotations are propagated from the revisionTemplate -> Revision -> PA. While the ownership is in place, the revision will be rereconciled if the annotations are changed. Maybe we should not do that and allow the mutation of annotations on revisions out of band? @mattmoor confirmed today that only the Revision.Spec is immutable. Metadata is not.

[yanweiguo]

Annotations are propagated from the revisionTemplate -> Revision -> PA. While the ownership is in place, the revision will be rereconciled if the annotations are changed. Maybe we should not do that and allow the mutation of annotations on revisions out of band? @mattmoor confirmed today that only the Revision.Spec is immutable. Metadata is not.

Then I think this request makes sense.

[lvjing2]

@markusthoemmes @yanweiguo Hi, sorry for late. What I know about our reconciler is same as @mattmoor that only the spec is immutable, and the metadata is not. And I have already implemented this in our cluster, it helps a lot for us to update the min/max replicas without creating a new revision. so I am glad to apply this to out HEAD.

[lvjing2]

/assign