embed: add "InitialElectionTickAdvance"

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

embed/config.go

@@ -123,6 +123,36 @@ type Config struct {
 	// make ticks a cluster wide configuration.
 	TickMs     uint `json:"heartbeat-interval"`
 	ElectionMs uint `json:"election-timeout"`
+
+	// InitialElectionTickAdvance is true, then local member fast-forwards
+	// election ticks to speed up "initial" leader election trigger. This
+	// benefits the case of larger election ticks. For instance, cross
+	// datacenter deployment may require longer election timeout of 10-second.
+	// If true, local node does not need wait up to 10-second. Instead,
+	// forwards its election ticks to 8-second, and have only 2-second left
+	// before leader election.
+	//
+	// Major assumptions are that:
+	//  - cluster has no active leader thus advancing ticks enables faster
+	//    leader election, or
+	//  - cluster already has an established leader, and rejoining follower
+	//    is likely to receive heartbeats from the leader after tick advance
+	//    and before election timeout.
+	//
+	// However, when network from leader to rejoining follower is congested,
+	// and the follower does not receive leader heartbeat within left election
+	// ticks, disruptive election has to happen thus affecting cluster
+	// availabilities.
+	//
+	// Disabling this would slow down initial bootstrap process for cross
+	// datacenter deployments. Make your own tradeoffs by configuring
+	// --initial-election-tick-advance at the cost of slow initial bootstrap.
+	//
+	// If single-node, it advances ticks regardless.
+	//
+	// See https://github.com/coreos/etcd/issues/9333 for more detail.
+	InitialElectionTickAdvance bool `json:"initial-election-tick-advance"`
+
 	QuotaBackendBytes int64 `json:"quota-backend-bytes"`
 	MaxTxnOps         uint  `json:"max-txn-ops"`
 	MaxRequestBytes   uint  `json:"max-request-bytes"`
@@ -307,6 +337,7 @@ func NewConfig() *Config {
 
 		TickMs:                     100,
 		ElectionMs:                 1000,
+		InitialElectionTickAdvance: true,
 
 		LPUrls: []url.URL{*lpurl},
 		LCUrls: []url.URL{*lcurl},

embed/etcd.go

@@ -174,6 +174,7 @@ func StartEtcd(inCfg *Config) (e *Etcd, err error) {
 		PeerTLSInfo:                cfg.PeerTLSInfo,
 		TickMs:                     cfg.TickMs,
 		ElectionTicks:              cfg.ElectionTicks(),
+		InitialElectionTickAdvance: cfg.InitialElectionTickAdvance,
 		AutoCompactionRetention:    autoCompactionRetention,
 		AutoCompactionMode:         cfg.AutoCompactionMode,
 		QuotaBackendBytes:          cfg.QuotaBackendBytes,