while trying to figure out why it takes so long to install Single node OpenShift I noticed that the kube-controller-manager cluster operator is degraded for ~5 minutes due to:
GarbageCollectorDegraded: error fetching rules: Get "https://thanos-querier.openshift-monitoring.svc:9091/api/v1/rules": dial tcp 172.30.119.108:9091: connect: connection refused
I don't understand how the prometheusClient is successfully initialized, but we get a connection refused once we try to query the rules.
Note that if the client initialization fails the kube-controller-manger won't set the  GarbageCollectorDegraded to true.

4.12

100%

1. install SNO with bootstrap in place (https://github.com/eranco74/bootstrap-in-place-poc)

2. monitor the cluster operators staus 

GarbageCollectorDegraded: error fetching rules: Get "https://thanos-querier.openshift-monitoring.svc:9091/api/v1/rules": dial tcp 172.30.119.108:9091: connect: connection refused 

Expected the GarbageCollectorDegraded status to be false

It seems that for PrometheusClient to be successfully initialised it needs to successfully create a connection but we get connection refused once we make the query.
Note that installing SNO with this patch (https://github.com/eranco74/cluster-kube-controller-manager-operator/commit/26e644503a8f04aa6d116ace6b9eb7b9b9f2f23f) reduces the installation time by 3 minutes