fix: readiness needs to be like liveness (#9941)

Readiness as no reasoning to be cluster scope
because that is not how the k8s networking works
for pods, all the pods to a deployment are not
sharing the network in a singleton. Instead they
are run as local scopes to themselves, with
readiness failures the pod is potentially taken
out of the network to be resolvable - this
affects the distributed setup in myriad of
different ways.

Instead readiness should behave like liveness
with local scope alone, and should be a dummy
implementation.

This PR all the startup times and overal k8s
startup time dramatically improves.

Added another handler called as `/minio/health/cluster`
to understand the cluster scope health.

cmd/healthcheck-router.go

@@ -26,6 +26,7 @@ const (
 	healthCheckPath          = "/health"
 	healthCheckLivenessPath  = "/live"
 	healthCheckReadinessPath = "/ready"
+	healthCheckClusterPath   = "/cluster"
 	healthCheckPathPrefix    = minioReservedBucketPath + healthCheckPath
 )
 
@@ -35,6 +36,9 @@ func registerHealthCheckRouter(router *mux.Router) {
 	// Healthcheck router
 	healthRouter := router.PathPrefix(healthCheckPathPrefix).Subrouter()
 
+	// Cluster check handler to verify cluster is active
+	healthRouter.Methods(http.MethodGet).Path(healthCheckClusterPath).HandlerFunc(httpTraceAll(ClusterCheckHandler))
+
 	// Liveness handler
 	healthRouter.Methods(http.MethodGet).Path(healthCheckLivenessPath).HandlerFunc(httpTraceAll(LivenessCheckHandler))
 	healthRouter.Methods(http.MethodHead).Path(healthCheckLivenessPath).HandlerFunc(httpTraceAll(LivenessCheckHandler))