Add Tuning section to README.

README.md

@@ -1169,7 +1169,50 @@ openssl ca -config openssl.cnf -policy policy_anything -extensions ssl_client -o
 
 ### Tuning
 
-TODO
+The default settings in etcd should work well for installations on a local network where the average network latency is low.
+However, when using etcd across multiple data centers or over networks with high latency you may need to tweak the heartbeat and election timeout settings.
+
+The underlying distributed consensus protocol relies on two separate timeouts to ensure that nodes can handoff leadership if one stalls or goes offline.
+The first timeout is called the *Heartbeat Timeout*.
+This is the frequency with which the leader will notify followers that it is still the leader.
+etcd batches commands together for higher throughput so this heartbeat timeout is also a delay for how long it takes for commands to be committed.
+By default, etcd uses a `50ms` heartbeat timeout.
+
+The second timeout is the *Election Timeout*.
+This timeout is how long a follower node will go without hearing a heartbeat before attempting to become leader itself.
+By default, etcd uses a `200ms` election timeout.
+
+Adjusting these values is a trade off.
+Lowering the heartbeat timeout will cause individual commands to be committed faster but it will lower the overall throughput of etcd.
+If your etcd instances have low utilization then lowering the heartbeat timeout can improve your command response time.
+
+The election timeout should be set based on the heartbeat timeout and your network ping time between nodes.
+Election timeouts should be at least 10 times your ping time so it can account for variance in your network.
+For example, if the ping time between your nodes is 10ms then you should have at least a 100ms election timeout.
+
+You should also set your election timeout to at least 4 to 5 times your heartbeat timeout to account for variance in leader replication.
+For a heartbeat timeout of 50ms you should set your election timeout to at least 200ms - 250ms.
+
+You can override the default values on the command line:
+
+```sh
+# Command line arguments:
+$ etcd -peer-heartbeat-timeout=100 -peer-election-timeout=500
+
+# Environment variables:
+$ ETCD_PEER_HEARTBEAT_TIMEOUT=100 ETCD_PEER_ELECTION_TIMEOUT=500 etcd
+```
+
+Or you can set the values within the configuration file:
+
+```toml
+[peer]
+heartbeat_timeout = 100
+election_timeout = 100
+```
+
+The values are specified in milliseconds.
+
 
 ## Project Details
 

etcd.go

@@ -86,11 +86,11 @@ func main() {
 	ps := server.NewPeerServer(info.Name, config.DataDir, info.RaftURL, info.RaftListenHost, &peerTLSConfig, &info.RaftTLS, registry, store, config.SnapshotCount)
 	ps.MaxClusterSize = config.MaxClusterSize
 	ps.RetryTimes = config.MaxRetryAttempts
-	if config.HeartbeatTimeout > 0 {
-		ps.HeartbeatTimeout = time.Duration(config.HeartbeatTimeout) * time.Millisecond
+	if config.Peer.HeartbeatTimeout > 0 {
+		ps.HeartbeatTimeout = time.Duration(config.Peer.HeartbeatTimeout) * time.Millisecond
 	}
-	if config.ElectionTimeout > 0 {
-		ps.ElectionTimeout = time.Duration(config.ElectionTimeout) * time.Millisecond
+	if config.Peer.ElectionTimeout > 0 {
+		ps.ElectionTimeout = time.Duration(config.Peer.ElectionTimeout) * time.Millisecond
 	}
 
 	// Create client server.

server/config.go

@@ -67,14 +67,14 @@ type Config struct {
 	ShowVersion      bool
 	Verbose          bool `toml:"verbose" env:"ETCD_VERBOSE"`
 	VeryVerbose      bool `toml:"very_verbose" env:"ETCD_VERY_VERBOSE"`
-	HeartbeatTimeout int  `toml:"peer_heartbeat_timeout" env:"ETCD_PEER_HEARTBEAT_TIMEOUT"`
-	ElectionTimeout  int  `toml:"peer_election_timeout" env:"ETCD_PEER_ELECTION_TIMEOUT"`
 	Peer             struct {
 		Addr     string `toml:"addr" env:"ETCD_PEER_ADDR"`
 		BindAddr string `toml:"bind_addr" env:"ETCD_PEER_BIND_ADDR"`
 		CAFile   string `toml:"ca_file" env:"ETCD_PEER_CA_FILE"`
 		CertFile string `toml:"cert_file" env:"ETCD_PEER_CERT_FILE"`
 		KeyFile  string `toml:"key_file" env:"ETCD_PEER_KEY_FILE"`
+		HeartbeatTimeout int  `toml:"heartbeat_timeout" env:"ETCD_PEER_HEARTBEAT_TIMEOUT"`
+		ElectionTimeout  int  `toml:"election_timeout" env:"ETCD_PEER_ELECTION_TIMEOUT"`
 	}
 }
 
@@ -86,10 +86,10 @@ func NewConfig() *Config {
 	c.MaxClusterSize = 9
 	c.MaxResultBuffer = 1024
 	c.MaxRetryAttempts = 3
-	c.Peer.Addr = "127.0.0.1:7001"
 	c.SnapshotCount = 10000
-	c.ElectionTimeout = 0
-	c.HeartbeatTimeout = 0
+	c.Peer.Addr = "127.0.0.1:7001"
+	c.Peer.HeartbeatTimeout = 0
+	c.Peer.ElectionTimeout = 0
 	return c
 }
 
@@ -236,8 +236,8 @@ func (c *Config) LoadFlags(arguments []string) error {
 	f.IntVar(&c.MaxResultBuffer, "max-result-buffer", c.MaxResultBuffer, "")
 	f.IntVar(&c.MaxRetryAttempts, "max-retry-attempts", c.MaxRetryAttempts, "")
 	f.IntVar(&c.MaxClusterSize, "max-cluster-size", c.MaxClusterSize, "")
-	f.IntVar(&c.HeartbeatTimeout, "peer-heartbeat-timeout", c.HeartbeatTimeout, "")
-	f.IntVar(&c.ElectionTimeout, "peer-election-timeout", c.ElectionTimeout, "")
+	f.IntVar(&c.Peer.HeartbeatTimeout, "peer-heartbeat-timeout", c.Peer.HeartbeatTimeout, "")
+	f.IntVar(&c.Peer.ElectionTimeout, "peer-election-timeout", c.Peer.ElectionTimeout, "")
 
 	f.StringVar(&cors, "cors", "", "")