client-go: Add metrics into informer

[chenk008]

Enhancement Description

• One-line enhancement description (can be used as a release note):
  Add metrics into informer.

• Kubernetes Enhancement Proposal: KEP-4346: client-go: Add informer metrics #4349

• Discussion Link: client-go: Add metrics into Informer kubernetes#122067

• Primary contact (assignee): @chenk008

• Responsible SIGs:
  sig/api-machinery

• Enhancement target (which target equals to which milestone):

  • Alpha release target (v1.30):
  • Beta release target (v1.31):
  • Stable release target (v1.33):

• Alpha

  • KEP (k/enhancements) update PR(s):
    • KEP-4346: client-go: Add informer metrics #4349 Initial KEP PR
    • Supplement for KEP-4346 #4504 Add missing push
    • KEP-4346: add PRR metadata file for 4346 #4511 Add PRR metadata file
  • Code (k/k) update PR(s):
    • Introduce reflector metrics with featuregate InformerMetrics kubernetes#123367
    • [WIP] Introduce informer fifo/handler metrics kubernetes#123510
  • Docs (k/website) update PR(s):
    • [WIP] [KEP-4346]: feature-gate InformerMetrics to alpha website#45273

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

[chenk008]

/sig api-machinery

[chenk008]

related issue:
https://github.com/kubernetes/client-go/issues/1027
kubernetes-sigs/controller-runtime#817
kubernetes/kubernetes#121662
kubernetes/kubernetes#117123

[lzlaa]

It's useful to find out whether there are unhandled events received by reflector.

[fedebongio]

/assign @logicalhan

[jpbetz]

/label lead-opted-in
/milestone v1.30