In [1] we allow localhost etcd as a fallback for apiserver to connect with etcd. This is a useful failsafe, in case no other etcd member is reachable.

In some rare scenarios during bootstrapping the apiserver might end up reaching out to a scaling-up etcd member and returns a 500 error with:

 etcdserver: rpc not supported for learner

[1] https://github.com/openshift/library-go/blob/636f95d7aabaa2b46021985d2ce83bbb93fefc31/pkg/operator/configobserver/etcd/observe_etcd_endpoints.go#L141-L143    

seen in 4.17, 4.18 but is definitely longer standing

rarely, but can be grepped in loki

    1.
    2.
    3.
    

apiserver returns a 500 reaching an etcd learner 

apiserver should not error on reaching etcd learners