etcdserver/api/rafthttp: document round-trip metrics, clean up

Signed-off-by: Gyuho Lee <gyuhox@gmail.com>

etcdserver/api/rafthttp/metrics.go

@@ -53,7 +53,7 @@ var (
 		[]string{"From"},
 	)
 
-	rtts = prometheus.NewHistogramVec(prometheus.HistogramOpts{
+	rttSec = prometheus.NewHistogramVec(prometheus.HistogramOpts{
 		Namespace: "etcd",
 		Subsystem: "network",
 		Name:      "peer_round_trip_time_seconds",
@@ -72,5 +72,5 @@ func init() {
 	prometheus.MustRegister(receivedBytes)
 	prometheus.MustRegister(sentFailures)
 	prometheus.MustRegister(recvFailures)
-	prometheus.MustRegister(rtts)
+	prometheus.MustRegister(rttSec)
 }

etcdserver/api/rafthttp/probing_status.go

@@ -44,9 +44,10 @@ func addPeerToProber(lg *zap.Logger, p probing.Prober, id string, us []string) {
 		} else {
 			plog.Errorf("failed to add peer %s into prober", id)
 		}
-	} else {
-		go monitorProbingStatus(lg, s, id)
+		return
 	}
+
+	go monitorProbingStatus(lg, s, id)
 }
 
 func monitorProbingStatus(lg *zap.Logger, s probing.Status, id string) {
@@ -83,7 +84,8 @@ func monitorProbingStatus(lg *zap.Logger, s probing.Status, id string) {
 					plog.Warningf("the clock difference against peer %s is too high [%v > %v]", id, s.ClockDiff(), time.Second)
 				}
 			}
-			rtts.WithLabelValues(id).Observe(s.SRTT().Seconds())
+			rttSec.WithLabelValues(id).Observe(s.SRTT().Seconds())
+
 		case <-s.StopNotify():
 			return
 		}