Consider adding liveness/readiness probes and metrics endpoint to test extension

[sbueringer]

To make our test extension / the reference implementation more production ready it would be great if we have readiness/liveness and metrics endpoints.

Details

I think we have at least two options:

• start a manager which gives us the additional endpoints always for free
  • we have to figure out how that can work with our custom extension server (which uses a webhook server underneath)
• implement similar endpoints as CR in our webhook server library

It would be great if we could also use the webhookServer.StartedChecker for our liveness/readiness endpoints like we do in our controllers here:

cluster-api/main.go

Lines 284 to 292 in 73f436e

	if err := mgr.AddReadyzCheck("webhook", mgr.GetWebhookServer().StartedChecker()); err != nil {
	setupLog.Error(err, "unable to create ready check")
	os.Exit(1)
	}
	if err := mgr.AddHealthzCheck("webhook", mgr.GetWebhookServer().StartedChecker()); err != nil {
	setupLog.Error(err, "unable to create health check")
	os.Exit(1)
	}

P.S. tilt-prepare already modifies our test extension deployment as if it would have a metrics endpoint (it adds the metrics port)

/area topology
/kind feature

[sbueringer]

cc @killianmuldoon

[fabriziopandini]

That's a nice improvement!
/triage accepted

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/lifecycle stale

[fabriziopandini]

/lifecycle frozen