[3.5] enhance health check endpoint to support serializable request

[ahrtr]

Backport the PR 13399 to 3.5.

cc @serathius @spzala @hexfusion @ptabor

[serathius]

Not sure about backporting features, would want to wait for @spzala opinion.

[ahrtr]

Not sure about backporting features, would want to wait for @spzala opinion.

Actually we can regard it as a bug, because etcd doesn't process health check properly.

[ptabor]

I think cherry picking is OK from pragmatic perspective for low/risk / absolutely no behavioural changes,
taking in consideration the complexity of major etcd version upgrade.

[serathius]

Makes sense

[moonovo]

@ahrtr please, how to use health check in k8s livenessProbe when client-cert-auth is enabled

[ahrtr]

@ahrtr please, how to use health check in k8s livenessProbe when client-cert-auth is enabled

health/serializable=true and set schema as HTTPS

[moonovo]

Thanks for your reply, when client-cert-auth enabled, etcd will verify client certificate. see listener.go#L483.
but the certificate cannot be configured for the k8s livenessProbe. There seems to be no way to use /health with client-cert-auth enabled.

[ahrtr]

Please have a try on 3.5.2 or the main branch, and let me know if you run into any issue.

[moonovo]

I opened an issue 13849.

[serathius]

I think that's a goal of client-cert-auth to require client provide certificates :P
I don't think it's a bug, but a feature that might be worth implementing