embed: advance ticks on restart

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

embed/etcd.go

@@ -199,11 +199,44 @@ func StartEtcd(inCfg *Config) (e *Etcd, err error) {
 			return e, err
 		}
 	}
+
+	restarted := e.Server.IsRestarted()
+	clusterN := len(e.Server.Cluster().Members())
+
+	// bootstrapping to fresh cluster, or single-node;
+	// advance ticks before starting Raft
+	needAdv := !restarted && clusterN == 1
+	if needAdv {
+		ticks := srvcfg.ElectionTicks - 1
+		plog.Infof("%s is advancing %d ticks for faster election (election tick %d, restarted '%v', %d found peer(s))", e.Server.ID(), ticks, srvcfg.ElectionTicks, restarted, clusterN)
+		e.Server.AdvanceRaftTicks(ticks)
+		needAdv = false
+	}
 	e.Server.Start()
 
 	if err = e.servePeers(); err != nil {
 		return e, err
 	}
+
+	// have not advanced ticks yet AND restarted,
+	// BUT no active peers have been found yet
+	actives := e.Server.CountActivePeers()
+	if !needAdv && restarted && actives == 0 {
+		// restart node, but we still want to advance ticks
+		// because even after starting peer transport
+		// no active peers have been found, maybe this node
+		// is the first node that started
+		// instead, adjust ticks to lower value in case
+		// active leader sends heartbeats to this node
+		// thus preventing disruptive elections
+		ticks := srvcfg.ElectionTicks / 10
+		plog.Infof("%s is advancing %d ticks after serving peers (election tick %d, restarted '%v', %d found peer(s))", e.Server.ID(), ticks, srvcfg.ElectionTicks, restarted, actives)
+		e.Server.AdvanceRaftTicks(ticks)
+		needAdv = false
+	} else {
+		plog.Infof("%s started serving peers with %d found peer(s) (no fast-forwarding election ticks after serving peers)", e.Server.ID(), actives)
+	}
+
 	if err = e.serveClients(); err != nil {
 		return e, err
 	}