exposing hashed storage versions via the discovery API

Enhancement Description

• One-line enhancement description (can be used as a release note): exposing hashed storage versions via the discovery API
• Kubernetes Enhancement Proposal: https://github.com/kubernetes/enhancements/tree/master/keps/sig-api-machinery/2342-exposing-hashed-storage-versions-via-the-discovery-API
  We propose to expose the hashed storage versions in the discovery API.

Motivation

We intend to use the exposed storage version hash to trigger the storage
version migrator.

In short, the storage version migrator detects if objects in etcd are stored in
a version different than the configured storage version. If so, the migrator
issues no-op update for the objects to migrate them to the storage version.

The storage version migrator can keep track of the versions the objects are
stored as. However, today the migrator has no way to tell what the expected
storage versions are. Thus we propose to expose this piece of information via
the discovery API.

• Discussion Link:
• Primary contact (assignee): @caesarxuchao
• Responsible SIGs: sig-api-machinery
• Enhancement target (which target equals to which milestone):
  • Alpha release target (x.y): 1.14
  • Beta release target (x.y): 1.15
  • Stable release target (x.y):
• Alpha
  • KEP (k/enhancements) update PR(s): [KEP] Adding StorageVersionHash to the discovery API #675
  • Code (k/k) update PR(s):
    • Populate the storage version hash kubernetes#72942
    • Adding the storage version hash to the discovery API kubernetes#73191
  • Docs (k/website) update PR(s):
• Beta
  • KEP (k/enhancements) update PR(s):
  • Code (k/k) update PR(s): Graduate storageVersionHash field in the discovery doc to beta kubernetes#78325
  • Docs (k/website) update(s):

Please keep this description up to date. This will help the Enhancement Team to track the evolution of the enhancement efficiently.

#2331 created for migrating the old keps into new template.

[lasomethingsomething]

/sig api-machinery

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[pacoxu]

/reopen
@caesarxuchao @roycaihw @liggitt

	genericfeatures.StorageVersionHash: {
		{Version: version.MustParse("1.14"), Default: false, PreRelease: featuregate.Alpha},
		{Version: version.MustParse("1.15"), Default: true, PreRelease: featuregate.Beta},
	},

The feature gate StorageVersionHash keeps beta for a long time. Do we want to promote it to GA?

BTW, https://github.com/kubernetes-sigs/kube-storage-version-migrator has no update for 2 years.