Make the readiness check fail for learner

[gojoy]

What would you like to be added?

RPC read and write operations are not supported for learners, so the readyz check should fail for the learner.

Why is this needed?

When the etcd cluster is running in Kubernetes, the learner's readiness probe should fail. #16007

[siyuanfoundation]

Thanks @gojoy for raising the issue. Would you be able to write a PR for this? It is pretty straightforward to add a check in

etcd/server/etcdserver/api/etcdhttp/health.go

Line 246 in 3cf550d

func installReadyzEndpoints(lg *zap.Logger, mux *http.ServeMux, server ServerHealth) {

based on the server method

etcd/server/etcdserver/server.go

Line 2485 in 3cf550d

func (s *EtcdServer) IsLearner() bool {

and then backport to 3.5, 3.4

[gojoy]

ok, please assign this to me @siyuanfoundation

[Dhairya-Dudhatra]

Can admin please assign this issue to me @siyuanfoundation

[siyuanfoundation]

/assign @gojoy