feat: implement standby mode

Change log: 1. PeerServer - estimate initial mode from its log through removedInLog variable - refactor FindCluster to return the estimation - refactor Start to call FindCluster explicitly - move raftServer start and cluster init from FindCluster to Start - remove stopNotify from PeerServer because it is not used anymore 2. Etcd - refactor Run logic to fit the specification 3. ClusterConfig - rename promoteDelay to removeDelay for better naming - add SyncClusterInterval field to ClusterConfig - commit command to set default cluster config when cluster is created - store cluster config info into key space for consistency - reload cluster config when reboot 4. add StandbyServer 5. Error - remove unused EcodePromoteError
2024-09-27 06:25:44 +00:00 · 2014-05-08 19:47:19 -07:00 · 2014-05-08 19:47:19 -07:00 · baadf63912
commit baadf63912
parent 5bd08a327d
22 changed files with 1186 additions and 384 deletions
--- a/error/error.go
+++ b/error/error.go
@ -52,12 +52,11 @@ var errors = map[int]string{
 	EcodeLeaderElect:  "During Leader Election",

 	// etcd related errors
-	EcodeWatcherCleared:      "watcher is cleared due to etcd recovery",
-	EcodeEventIndexCleared:   "The event in requested index is outdated and cleared",
-	EcodeStandbyInternal:     "Standby Internal Error",
-	EcodeInvalidActiveSize:   "Invalid active size",
-	EcodeInvalidPromoteDelay: "Standby promote delay",
-	EcodePromoteError:        "Standby promotion error",
+	EcodeWatcherCleared:     "watcher is cleared due to etcd recovery",
+	EcodeEventIndexCleared:  "The event in requested index is outdated and cleared",
+	EcodeStandbyInternal:    "Standby Internal Error",
+	EcodeInvalidActiveSize:  "Invalid active size",
+	EcodeInvalidRemoveDelay: "Standby remove delay",

 	// client related errors
 	EcodeClientInternal: "Client Internal Error",
@ -89,12 +88,11 @@ const (
 	EcodeRaftInternal = 300
 	EcodeLeaderElect  = 301

-	EcodeWatcherCleared      = 400
-	EcodeEventIndexCleared   = 401
-	EcodeStandbyInternal     = 402
-	EcodeInvalidActiveSize   = 403
-	EcodeInvalidPromoteDelay = 404
-	EcodePromoteError        = 405
+	EcodeWatcherCleared     = 400
+	EcodeEventIndexCleared  = 401
+	EcodeStandbyInternal    = 402
+	EcodeInvalidActiveSize  = 403
+	EcodeInvalidRemoveDelay = 404

 	EcodeClientInternal = 500
 )
--- a/etcd/etcd.go
+++ b/etcd/etcd.go
@ -17,12 +17,12 @@ limitations under the License.
 package etcd

 import (
-	"net"
 	"net/http"
 	"os"
 	"path/filepath"
 	"runtime"
 	"strings"
+	"sync"
 	"time"

 	goetcd "github.com/coreos/etcd/third_party/github.com/coreos/go-etcd/etcd"
@ -47,14 +47,23 @@ import (
 const extraTimeout = time.Duration(1000) * time.Millisecond

 type Etcd struct {
-	Config       *config.Config     // etcd config
-	Store        store.Store        // data store
-	Registry     *server.Registry   // stores URL information for nodes
-	Server       *server.Server     // http server, runs on 4001 by default
-	PeerServer   *server.PeerServer // peer server, runs on 7001 by default
-	listener     net.Listener       // Listener for Server
-	peerListener net.Listener       // Listener for PeerServer
-	readyC       chan bool          // To signal when server is ready to accept connections
+	Config *config.Config // etcd config
+
+	Store         store.Store        // data store
+	Registry      *server.Registry   // stores URL information for nodes
+	Server        *server.Server     // http server, runs on 4001 by default
+	PeerServer    *server.PeerServer // peer server, runs on 7001 by default
+	StandbyServer *server.StandbyServer
+
+	server     *http.Server
+	peerServer *http.Server
+
+	mode        Mode
+	modeMutex   sync.Mutex
+	closeChan   chan bool
+	readyNotify chan bool // To signal when server is ready to accept connections
+	onceReady   sync.Once
+	stopNotify  chan bool // To signal when server is stopped totally
 }

 // New returns a new Etcd instance.
@ -63,8 +72,10 @@ func New(c *config.Config) *Etcd {
 		c = config.New()
 	}
 	return &Etcd{
-		Config: c,
-		readyC: make(chan bool),
+		Config:      c,
+		closeChan:   make(chan bool),
+		readyNotify: make(chan bool),
+		stopNotify:  make(chan bool),
 	}
 }

@ -188,7 +199,7 @@ func (e *Etcd) Run() {

 	// Create raft transporter and server
 	raftTransporter := server.NewTransporter(followersStats, serverStats, e.Registry, heartbeatInterval, dialTimeout, responseHeaderTimeout)
-	if psConfig.Scheme == "https" {
+	if e.Config.PeerTLSInfo().Scheme() == "https" {
 		raftClientTLSConfig, err := e.Config.PeerTLSInfo().ClientConfig()
 		if err != nil {
 			log.Fatal("raft client TLS error: ", err)
@ -201,7 +212,7 @@ func (e *Etcd) Run() {
 	}
 	raftServer.SetElectionTimeout(electionTimeout)
 	raftServer.SetHeartbeatInterval(heartbeatInterval)
-	e.PeerServer.SetRaftServer(raftServer)
+	e.PeerServer.SetRaftServer(raftServer, e.Config.Snapshot)

 	// Create etcd server
 	e.Server = server.New(e.Config.Name, e.Config.Addr, e.PeerServer, e.Registry, e.Store, &mb)
@ -212,72 +223,179 @@ func (e *Etcd) Run() {

 	e.PeerServer.SetServer(e.Server)

+	// Create standby server
+	ssConfig := server.StandbyServerConfig{
+		Name:       e.Config.Name,
+		PeerScheme: e.Config.PeerTLSInfo().Scheme(),
+		PeerURL:    e.Config.Peer.Addr,
+		ClientURL:  e.Config.Addr,
+	}
+	e.StandbyServer = server.NewStandbyServer(ssConfig, client)
+
 	// Generating config could be slow.
 	// Put it here to make listen happen immediately after peer-server starting.
 	peerTLSConfig := server.TLSServerConfig(e.Config.PeerTLSInfo())
 	etcdTLSConfig := server.TLSServerConfig(e.Config.EtcdTLSInfo())

+	toStartPeerServer, possiblePeers, err := e.PeerServer.FindCluster(e.Config.Discovery, e.Config.Peers)
+	if err != nil {
+		log.Fatal(err)
+	}
+	if toStartPeerServer {
+		e.setMode(PeerMode)
+	} else {
+		e.StandbyServer.SyncCluster(possiblePeers)
+		e.setMode(StandbyMode)
+	}
+
+	serverHTTPHandler := &ehttp.CORSHandler{e.Server.HTTPHandler(), corsInfo}
+	peerServerHTTPHandler := &ehttp.CORSHandler{e.PeerServer.HTTPHandler(), corsInfo}
+	standbyServerHTTPHandler := &ehttp.CORSHandler{e.StandbyServer.ClientHTTPHandler(), corsInfo}
+
 	log.Infof("etcd server [name %s, listen on %s, advertised url %s]", e.Server.Name, e.Config.BindAddr, e.Server.URL())
-	e.listener = server.NewListener(e.Config.EtcdTLSInfo().Scheme(), e.Config.BindAddr, etcdTLSConfig)
+	listener := server.NewListener(e.Config.EtcdTLSInfo().Scheme(), e.Config.BindAddr, etcdTLSConfig)
+	e.server = &http.Server{Handler: &ModeHandler{e, serverHTTPHandler, standbyServerHTTPHandler}}
+	log.Infof("peer server [name %s, listen on %s, advertised url %s]", e.PeerServer.Config.Name, e.Config.Peer.BindAddr, e.PeerServer.Config.URL)
+	peerListener := server.NewListener(e.Config.PeerTLSInfo().Scheme(), e.Config.Peer.BindAddr, peerTLSConfig)
+	e.peerServer = &http.Server{Handler: &ModeHandler{e, peerServerHTTPHandler, http.NotFoundHandler()}}

-	// An error string equivalent to net.errClosing for using with
-	// http.Serve() during server shutdown. Need to re-declare
-	// here because it is not exported by "net" package.
-	const errClosing = "use of closed network connection"
-
-	peerServerClosed := make(chan bool)
+	wg := sync.WaitGroup{}
+	wg.Add(2)
 	go func() {
-		// Starting peer server should be followed close by listening on its port
-		// If not, it may leave many requests unaccepted, or cannot receive heartbeat from the cluster.
-		// One severe problem caused if failing receiving heartbeats is when the second node joins one-node cluster,
-		// the cluster could be out of work as long as the two nodes cannot transfer messages.
-		e.PeerServer.Start(e.Config.Snapshot, e.Config.Discovery, e.Config.Peers)
-
-		go func() {
-			select {
-			case <-e.PeerServer.StopNotify():
-			case <-e.PeerServer.RemoveNotify():
-				log.Infof("peer server is removed")
-				os.Exit(0)
-			}
-		}()
-
-		log.Infof("peer server [name %s, listen on %s, advertised url %s]", e.PeerServer.Config.Name, e.Config.Peer.BindAddr, e.PeerServer.Config.URL)
-		e.peerListener = server.NewListener(psConfig.Scheme, e.Config.Peer.BindAddr, peerTLSConfig)
-
-		close(e.readyC) // etcd server is ready to accept connections, notify waiters.
-
-		sHTTP := &ehttp.CORSHandler{e.PeerServer.HTTPHandler(), corsInfo}
-		if err := http.Serve(e.peerListener, sHTTP); err != nil {
-			if !strings.Contains(err.Error(), errClosing) {
+		<-e.readyNotify
+		defer wg.Done()
+		if err := e.server.Serve(listener); err != nil {
+			if !isListenerClosing(err) {
+				log.Fatal(err)
+			}
+		}
+	}()
+	go func() {
+		<-e.readyNotify
+		defer wg.Done()
+		if err := e.peerServer.Serve(peerListener); err != nil {
+			if !isListenerClosing(err) {
 				log.Fatal(err)
 			}
 		}
-		close(peerServerClosed)
 	}()

-	sHTTP := &ehttp.CORSHandler{e.Server.HTTPHandler(), corsInfo}
-	if err := http.Serve(e.listener, sHTTP); err != nil {
-		if !strings.Contains(err.Error(), errClosing) {
-			log.Fatal(err)
+	e.runServer()
+
+	listener.Close()
+	peerListener.Close()
+	wg.Wait()
+	log.Infof("etcd instance is stopped [name %s]", e.Config.Name)
+	close(e.stopNotify)
+}
+
+func (e *Etcd) runServer() {
+	var removeNotify <-chan bool
+	for {
+		if e.mode == PeerMode {
+			log.Infof("%v starts to run in peer mode", e.Config.Name)
+			// Starting peer server should be followed close by listening on its port
+			// If not, it may leave many requests unaccepted, or cannot receive heartbeat from the cluster.
+			// One severe problem caused if failing receiving heartbeats is when the second node joins one-node cluster,
+			// the cluster could be out of work as long as the two nodes cannot transfer messages.
+			e.PeerServer.Start(e.Config.Snapshot)
+			removeNotify = e.PeerServer.RemoveNotify()
+		} else {
+			log.Infof("%v starts to run in standby mode", e.Config.Name)
+			e.StandbyServer.Start()
+			removeNotify = e.StandbyServer.RemoveNotify()
+		}
+
+		// etcd server is ready to accept connections, notify waiters.
+		e.onceReady.Do(func() { close(e.readyNotify) })
+
+		select {
+		case <-e.closeChan:
+			e.PeerServer.Stop()
+			e.StandbyServer.Stop()
+			return
+		case <-removeNotify:
+		}
+
+		if e.mode == PeerMode {
+			peerURLs := e.Registry.PeerURLs(e.PeerServer.RaftServer().Leader(), e.Config.Name)
+			e.StandbyServer.SyncCluster(peerURLs)
+			e.setMode(StandbyMode)
+		} else {
+			// Generate new peer server here.
+			// TODO(yichengq): raft server cannot be started after stopped.
+			// It should be removed when raft restart is implemented.
+			heartbeatInterval := time.Duration(e.Config.Peer.HeartbeatInterval) * time.Millisecond
+			electionTimeout := time.Duration(e.Config.Peer.ElectionTimeout) * time.Millisecond
+			raftServer, err := raft.NewServer(e.Config.Name, e.Config.DataDir, e.PeerServer.RaftServer().Transporter(), e.Store, e.PeerServer, "")
+			if err != nil {
+				log.Fatal(err)
+			}
+			raftServer.SetElectionTimeout(electionTimeout)
+			raftServer.SetHeartbeatInterval(heartbeatInterval)
+			e.PeerServer.SetRaftServer(raftServer, e.Config.Snapshot)
+
+			e.PeerServer.SetJoinIndex(e.StandbyServer.JoinIndex())
+			e.setMode(PeerMode)
 		}
 	}
-
-	<-peerServerClosed
-	log.Infof("etcd instance is stopped [name %s]", e.Config.Name)
 }

 // Stop the etcd instance.
-//
-// TODO Shutdown gracefully.
 func (e *Etcd) Stop() {
-	e.PeerServer.Stop()
-	e.peerListener.Close()
-	e.listener.Close()
+	close(e.closeChan)
+	<-e.stopNotify
 }

 // ReadyNotify returns a channel that is going to be closed
 // when the etcd instance is ready to accept connections.
 func (e *Etcd) ReadyNotify() <-chan bool {
-	return e.readyC
+	return e.readyNotify
 }
+
+func (e *Etcd) Mode() Mode {
+	e.modeMutex.Lock()
+	defer e.modeMutex.Unlock()
+	return e.mode
+}
+
+func (e *Etcd) setMode(m Mode) {
+	e.modeMutex.Lock()
+	defer e.modeMutex.Unlock()
+	e.mode = m
+}
+
+func isListenerClosing(err error) bool {
+	// An error string equivalent to net.errClosing for using with
+	// http.Serve() during server shutdown. Need to re-declare
+	// here because it is not exported by "net" package.
+	const errClosing = "use of closed network connection"
+
+	return strings.Contains(err.Error(), errClosing)
+}
+
+type ModeGetter interface {
+	Mode() Mode
+}
+
+type ModeHandler struct {
+	ModeGetter
+	PeerModeHandler    http.Handler
+	StandbyModeHandler http.Handler
+}
+
+func (h *ModeHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	switch h.Mode() {
+	case PeerMode:
+		h.PeerModeHandler.ServeHTTP(w, r)
+	case StandbyMode:
+		h.StandbyModeHandler.ServeHTTP(w, r)
+	}
+}
+
+type Mode int
+
+const (
+	PeerMode Mode = iota
+	StandbyMode
+)
--- a/scripts/test-cluster
+++ b/scripts/test-cluster
@ -31,7 +31,7 @@ done
 tmux new-window -t $SESSION:2 -n 'proxy'
 tmux split-window -h
 tmux select-pane -t 0
-tmux send-keys "curl -XPUT -H \"Content-Type: application/json\" -d '{\"activeSize\":3, \"promoteDelay\":30}' http://127.0.0.1:7001/v2/admin/config" C-m
+tmux send-keys "curl -XPUT -H \"Content-Type: application/json\" -d '{\"activeSize\":3, \"removeDelay\":30}' http://127.0.0.1:7001/v2/admin/config" C-m

 for i in 4 5 6; do
 	tmux select-pane -t 0
--- a/server/client.go
+++ b/server/client.go
@ -30,7 +30,7 @@ func NewClient(transport http.RoundTripper) *Client {
 	return &Client{http.Client{Transport: transport}}
 }

-// CheckVersion checks whether the version is available.
+// CheckVersion returns true when the version check on the server returns 200.
 func (c *Client) CheckVersion(url string, version int) (bool, *etcdErr.Error) {
 	resp, err := c.Get(url + fmt.Sprintf("/version/%d/check", version))
 	if err != nil {
--- a/server/cluster_config.go
+++ b/server/cluster_config.go
@ -11,11 +11,17 @@ const (
 	// MinActiveSize is the minimum active size allowed.
 	MinActiveSize = 3

-	// DefaultPromoteDelay is the default elapsed time before promotion.
-	DefaultPromoteDelay = int((30 * time.Minute) / time.Second)
+	// DefaultRemoveDelay is the default elapsed time before promotion.
+	DefaultRemoveDelay = int((30 * time.Minute) / time.Second)

-	// MinPromoteDelay is the minimum promote delay allowed.
-	MinPromoteDelay = int((2 * time.Second) / time.Second)
+	// MinRemoveDelay is the minimum promote delay allowed.
+	MinRemoveDelay = int((2 * time.Second) / time.Second)
+
+	// DefaultSyncClusterInterval is the default interval for cluster sync.
+	DefaultSyncClusterInterval = int((30 * time.Minute) / time.Second)
+
+	// MinSyncClusterInterval is the minimum sync interval allowed.
+	MinSyncClusterInterval = int((1 * time.Second) / time.Second)
 )

 // ClusterConfig represents cluster-wide configuration settings.
@ -25,15 +31,20 @@ type ClusterConfig struct {
 	// Nodes that join the cluster after the limit is reached are standbys.
 	ActiveSize int `json:"activeSize"`

-	// PromoteDelay is the amount of time, in seconds, after a node is
-	// unreachable that it will be swapped out for a standby node, if available.
-	PromoteDelay int `json:"promoteDelay"`
+	// RemoveDelay is the amount of time, in seconds, after a node is
+	// unreachable that it will be swapped out as a standby node.
+	RemoveDelay int `json:"removeDelay"`
+
+	// SyncClusterInterval is the amount of time, in seconds, between
+	// cluster sync when it runs in standby mode.
+	SyncClusterInterval int `json:"syncClusterInterval"`
 }

 // NewClusterConfig returns a cluster configuration with default settings.
 func NewClusterConfig() *ClusterConfig {
 	return &ClusterConfig{
-		ActiveSize:   DefaultActiveSize,
-		PromoteDelay: DefaultPromoteDelay,
+		ActiveSize:          DefaultActiveSize,
+		RemoveDelay:         DefaultRemoveDelay,
+		SyncClusterInterval: DefaultSyncClusterInterval,
 	}
 }
--- a/server/join_command.go
+++ b/server/join_command.go
@ -61,6 +61,9 @@ func applyJoin(c *JoinCommand, context raft.Context) (uint64, error) {
 				return 0, err
 			}
 		}
+		if c.Name == context.Server().Name() {
+			ps.removedInLog = false
+		}
 		return commitIndex, nil
 	}

@ -74,7 +77,9 @@ func applyJoin(c *JoinCommand, context raft.Context) (uint64, error) {
 	}

 	// Check peer number in the cluster
-	if ps.registry.Count() >= ps.ClusterConfig().ActiveSize {
+	count := ps.registry.Count()
+	// ClusterConfig doesn't init until first machine is added
+	if count > 0 && count >= ps.ClusterConfig().ActiveSize {
 		log.Debug("Reject join request from ", c.Name)
 		return 0, etcdErr.NewError(etcdErr.EcodeNoMorePeer, "", context.CommitIndex())
 	}
@ -93,6 +98,9 @@ func applyJoin(c *JoinCommand, context raft.Context) (uint64, error) {
 		ps.followersStats.Followers[c.Name].Latency.Minimum = 1 << 63
 	}

+	if c.Name == context.Server().Name() {
+		ps.removedInLog = false
+	}
 	return commitIndex, nil
 }

--- a/server/peer_server.go
+++ b/server/peer_server.go
@ -35,6 +35,9 @@ const (
 	// PeerActivityMonitorTimeout is the time between checks for dead nodes in
 	// the cluster.
 	PeerActivityMonitorTimeout = 1 * time.Second
+
+	// The location of cluster config in key space.
+	ClusterConfigKey = "/_etcd/config"
 )

 type PeerServerConfig struct {
@ -49,17 +52,18 @@ type PeerServerConfig struct {
 type PeerServer struct {
 	Config         PeerServerConfig
 	client         *Client
-	clusterConfig  *ClusterConfig
 	raftServer     raft.Server
 	server         *Server
-	joinIndex      uint64
 	followersStats *raftFollowersStats
 	serverStats    *raftServerStats
 	registry       *Registry
 	store          store.Store
 	snapConf       *snapshotConf

-	stopNotify           chan bool
+	joinIndex    uint64
+	isNewCluster bool
+	removedInLog bool
+
 	removeNotify         chan bool
 	started              bool
 	closeChan            chan bool
@ -87,7 +91,6 @@ func NewPeerServer(psConfig PeerServerConfig, client *Client, registry *Registry
 	s := &PeerServer{
 		Config:         psConfig,
 		client:         client,
-		clusterConfig:  NewClusterConfig(),
 		registry:       registry,
 		store:          store,
 		followersStats: followersStats,
@ -101,7 +104,7 @@ func NewPeerServer(psConfig PeerServerConfig, client *Client, registry *Registry
 	return s
 }

-func (s *PeerServer) SetRaftServer(raftServer raft.Server) {
+func (s *PeerServer) SetRaftServer(raftServer raft.Server, snapshot bool) {
 	s.snapConf = &snapshotConf{
 		checkingInterval: time.Second * 3,
 		// this is not accurate, we will update raft to provide an api
@ -120,130 +123,7 @@ func (s *PeerServer) SetRaftServer(raftServer raft.Server) {
 	raftServer.AddEventListener(raft.HeartbeatEventType, s.recordMetricEvent)

 	s.raftServer = raftServer
-}
-
-// ClusterConfig retrieves the current cluster configuration.
-func (s *PeerServer) ClusterConfig() *ClusterConfig {
-	return s.clusterConfig
-}
-
-// SetClusterConfig updates the current cluster configuration.
-// Adjusting the active size will cause the PeerServer to demote peers or
-// promote standbys to match the new size.
-func (s *PeerServer) SetClusterConfig(c *ClusterConfig) {
-	// Set minimums.
-	if c.ActiveSize < MinActiveSize {
-		c.ActiveSize = MinActiveSize
-	}
-	if c.PromoteDelay < MinPromoteDelay {
-		c.PromoteDelay = MinPromoteDelay
-	}
-
-	s.clusterConfig = c
-}
-
-// Try all possible ways to find clusters to join
-// Include log data in -data-dir, -discovery and -peers
-//
-// Peer discovery follows this order:
-// 1. previous peers in -data-dir
-// 2. -discovery
-// 3. -peers
-//
-// TODO(yichengq): RaftServer should be started as late as possible.
-// Current implementation to start it is not that good,
-// and should be refactored later.
-func (s *PeerServer) findCluster(discoverURL string, peers []string) {
-	name := s.Config.Name
-	isNewNode := s.raftServer.IsLogEmpty()
-
-	// Try its best to find possible peers, and connect with them.
-	if !isNewNode {
-		// It is not allowed to join the cluster with existing peer address
-		// This prevents old node joining with different name by mistake.
-		if !s.checkPeerAddressNonconflict() {
-			log.Fatalf("%v is not allowed to join the cluster with existing URL %v", s.Config.Name, s.Config.URL)
-		}
-
-		// Take old nodes into account.
-		allPeers := s.getKnownPeers()
-		// Discover registered peers.
-		// TODO(yichengq): It may mess up discoverURL if this is
-		// set wrong by mistake. This may need to refactor discovery
-		// module. Fix it later.
-		if discoverURL != "" {
-			discoverPeers, _ := s.handleDiscovery(discoverURL)
-			allPeers = append(allPeers, discoverPeers...)
-		}
-		allPeers = append(allPeers, peers...)
-		allPeers = s.removeSelfFromList(allPeers)
-
-		// If there is possible peer list, use it to find cluster.
-		if len(allPeers) > 0 {
-			// TODO(yichengq): joinCluster may fail if there's no leader for
-			// current cluster. It should wait if the cluster is under
-			// leader election, or the node with changed IP cannot join
-			// the cluster then.
-			if err := s.startAsFollower(allPeers, 1); err == nil {
-				log.Debugf("%s joins to the previous cluster %v", name, allPeers)
-				return
-			}
-
-			log.Warnf("%s cannot connect to previous cluster %v", name, allPeers)
-		}
-
-		// TODO(yichengq): Think about the action that should be done
-		// if it cannot connect any of the previous known node.
-		s.raftServer.Start()
-		log.Debugf("%s is restarting the cluster %v", name, allPeers)
-		return
-	}
-
-	// Attempt cluster discovery
-	if discoverURL != "" {
-		discoverPeers, discoverErr := s.handleDiscovery(discoverURL)
-		// It is registered in discover url
-		if discoverErr == nil {
-			// start as a leader in a new cluster
-			if len(discoverPeers) == 0 {
-				log.Debugf("%s is starting a new cluster via discover service", name)
-				s.startAsLeader()
-			} else {
-				log.Debugf("%s is joining a cluster %v via discover service", name, discoverPeers)
-				if err := s.startAsFollower(discoverPeers, s.Config.RetryTimes); err != nil {
-					log.Fatal(err)
-				}
-			}
-			return
-		}
-		log.Warnf("%s failed to connect discovery service[%v]: %v", name, discoverURL, discoverErr)
-
-		if len(peers) == 0 {
-			log.Fatalf("%s, the new leader, must register itself to discovery service as required", name)
-		}
-	}
-
-	if len(peers) > 0 {
-		if err := s.startAsFollower(peers, s.Config.RetryTimes); err != nil {
-			log.Fatalf("%s cannot connect to existing cluster %v", name, peers)
-		}
-		return
-	}
-
-	log.Infof("%s is starting a new cluster.", s.Config.Name)
-	s.startAsLeader()
-	return
-}
-
-// Start starts the raft server.
-// The function assumes that join has been accepted successfully.
-func (s *PeerServer) Start(snapshot bool, discoverURL string, peers []string) error {
-	s.Lock()
-	defer s.Unlock()
-	if s.started {
-		return nil
-	}
-	s.started = true
+	s.removedInLog = false

 	// LoadSnapshot
 	if snapshot {
@ -264,13 +144,142 @@ func (s *PeerServer) Start(snapshot bool, discoverURL string, peers []string) er
 			log.Warnf("Failed setting NOCOW: %v", err)
 		}
 	}
+}

-	s.findCluster(discoverURL, peers)
+// Try all possible ways to find clusters to join
+// Include log data in -data-dir, -discovery and -peers
+//
+// Peer discovery follows this order:
+// 1. previous peers in -data-dir
+// 2. -discovery
+// 3. -peers
+func (s *PeerServer) FindCluster(discoverURL string, peers []string) (toStart bool, possiblePeers []string, err error) {
+	name := s.Config.Name
+	isNewNode := s.raftServer.IsLogEmpty()
+
+	// Try its best to find possible peers, and connect with them.
+	if !isNewNode {
+		// It is not allowed to join the cluster with existing peer address
+		// This prevents old node joining with different name by mistake.
+		if !s.checkPeerAddressNonconflict() {
+			err = fmt.Errorf("%v is not allowed to join the cluster with existing URL %v", s.Config.Name, s.Config.URL)
+			return
+		}
+
+		// Take old nodes into account.
+		possiblePeers = s.getKnownPeers()
+		// Discover registered peers.
+		// TODO(yichengq): It may mess up discoverURL if this is
+		// set wrong by mistake. This may need to refactor discovery
+		// module. Fix it later.
+		if discoverURL != "" {
+			discoverPeers, _ := s.handleDiscovery(discoverURL)
+			possiblePeers = append(possiblePeers, discoverPeers...)
+		}
+		possiblePeers = append(possiblePeers, peers...)
+		possiblePeers = s.removeSelfFromList(possiblePeers)
+
+		if s.removedInLog {
+			return
+		}
+
+		// If there is possible peer list, use it to find cluster.
+		if len(possiblePeers) > 0 {
+			// TODO(yichengq): joinCluster may fail if there's no leader for
+			// current cluster. It should wait if the cluster is under
+			// leader election, or the node with changed IP cannot join
+			// the cluster then.
+			if rejected, ierr := s.startAsFollower(possiblePeers, 1); rejected {
+				log.Debugf("%s should work as standby for the cluster %v: %v", name, possiblePeers, ierr)
+				return
+			} else if ierr != nil {
+				log.Warnf("%s cannot connect to previous cluster %v: %v", name, possiblePeers, ierr)
+			} else {
+				log.Debugf("%s joins to the previous cluster %v", name, possiblePeers)
+				toStart = true
+				return
+			}
+		}
+
+		// TODO(yichengq): Think about the action that should be done
+		// if it cannot connect any of the previous known node.
+		log.Debugf("%s is restarting the cluster %v", name, possiblePeers)
+		toStart = true
+		return
+	}
+
+	// Attempt cluster discovery
+	if discoverURL != "" {
+		discoverPeers, discoverErr := s.handleDiscovery(discoverURL)
+		// It is registered in discover url
+		if discoverErr == nil {
+			// start as a leader in a new cluster
+			if len(discoverPeers) == 0 {
+				s.isNewCluster = true
+				log.Debugf("%s is starting a new cluster via discover service", name)
+				toStart = true
+				return
+			}
+
+			log.Debugf("%s is joining a cluster %v via discover service", name, discoverPeers)
+			if rejected, ierr := s.startAsFollower(discoverPeers, s.Config.RetryTimes); rejected {
+				log.Debugf("%s should work as standby for the cluster %v: %v", name, discoverPeers, ierr)
+				possiblePeers = discoverPeers
+			} else if ierr != nil {
+				log.Warnf("%s cannot connect to existing cluster %v: %v", name, discoverPeers, ierr)
+				err = ierr
+			} else {
+				toStart = true
+			}
+			return
+		}
+		log.Warnf("%s failed to connect discovery service[%v]: %v", name, discoverURL, discoverErr)
+
+		if len(peers) == 0 {
+			err = fmt.Errorf("%s, the new instance, must register itself to discovery service as required", name)
+			return
+		}
+	}
+
+	if len(peers) > 0 {
+		log.Debugf("%s is joining peers %v from -peers flag", name, peers)
+		if rejected, ierr := s.startAsFollower(peers, s.Config.RetryTimes); rejected {
+			log.Debugf("%s should work as standby for the cluster %v: %v", name, peers, ierr)
+			possiblePeers = peers
+		} else if ierr != nil {
+			log.Warnf("%s cannot connect to existing peers %v: %v", name, peers, ierr)
+			err = ierr
+		} else {
+			toStart = true
+		}
+		return
+	}
+
+	s.isNewCluster = true
+	log.Infof("%s is starting a new cluster.", s.Config.Name)
+	toStart = true
+	return
+}
+
+// Start starts the raft server.
+// The function assumes that join has been accepted successfully.
+func (s *PeerServer) Start(snapshot bool) error {
+	s.Lock()
+	defer s.Unlock()
+	if s.started {
+		return nil
+	}
+	s.started = true

-	s.stopNotify = make(chan bool)
 	s.removeNotify = make(chan bool)
 	s.closeChan = make(chan bool)

+	s.raftServer.Start()
+	if s.isNewCluster {
+		s.InitNewCluster()
+		s.isNewCluster = false
+	}
+
 	s.startRoutine(s.monitorSync)
 	s.startRoutine(s.monitorTimeoutThreshold)
 	s.startRoutine(s.monitorActiveSize)
@ -298,7 +307,6 @@ func (s *PeerServer) Stop() {
 	// but this functionality has not been implemented.
 	s.raftServer.Stop()
 	s.routineGroup.Wait()
-	close(s.stopNotify)
 }

 // asyncRemove stops the server in peer mode.
@ -326,11 +334,6 @@ func (s *PeerServer) asyncRemove() {
 	}()
 }

-// StopNotify notifies the server is stopped.
-func (s *PeerServer) StopNotify() <-chan bool {
-	return s.stopNotify
-}
-
 // RemoveNotify notifies the server is removed from peer mode due to
 // removal from the cluster.
 func (s *PeerServer) RemoveNotify() <-chan bool {
@ -362,6 +365,48 @@ func (s *PeerServer) HTTPHandler() http.Handler {
 	return router
 }

+func (s *PeerServer) SetJoinIndex(joinIndex uint64) {
+	s.joinIndex = joinIndex
+}
+
+// ClusterConfig retrieves the current cluster configuration.
+func (s *PeerServer) ClusterConfig() *ClusterConfig {
+	e, err := s.store.Get(ClusterConfigKey, false, false)
+	// This is useful for backward compatibility because it doesn't
+	// set cluster config in older version.
+	if err != nil {
+		log.Debugf("failed getting cluster config key: %v", err)
+		return NewClusterConfig()
+	}
+
+	var c ClusterConfig
+	if err = json.Unmarshal([]byte(*e.Node.Value), &c); err != nil {
+		log.Debugf("failed unmarshaling cluster config: %v", err)
+		return NewClusterConfig()
+	}
+	return &c
+}
+
+// SetClusterConfig updates the current cluster configuration.
+// Adjusting the active size will cause the PeerServer to demote peers or
+// promote standbys to match the new size.
+func (s *PeerServer) SetClusterConfig(c *ClusterConfig) {
+	// Set minimums.
+	if c.ActiveSize < MinActiveSize {
+		c.ActiveSize = MinActiveSize
+	}
+	if c.RemoveDelay < MinRemoveDelay {
+		c.RemoveDelay = MinRemoveDelay
+	}
+	if c.SyncClusterInterval < MinSyncClusterInterval {
+		c.SyncClusterInterval = MinSyncClusterInterval
+	}
+
+	log.Debugf("set cluster config as %v", c)
+	b, _ := json.Marshal(c)
+	s.store.Set(ClusterConfigKey, false, string(b), store.Permanent)
+}
+
 // Retrieves the underlying Raft server.
 func (s *PeerServer) RaftServer() raft.Server {
 	return s.raftServer
@ -372,40 +417,48 @@ func (s *PeerServer) SetServer(server *Server) {
 	s.server = server
 }

-func (s *PeerServer) startAsLeader() {
-	s.raftServer.Start()
+func (s *PeerServer) InitNewCluster() {
 	// leader need to join self as a peer
+	s.doCommand(&JoinCommand{
+		MinVersion: store.MinVersion(),
+		MaxVersion: store.MaxVersion(),
+		Name:       s.raftServer.Name(),
+		RaftURL:    s.Config.URL,
+		EtcdURL:    s.server.URL(),
+	})
+	log.Debugf("%s start as a leader", s.Config.Name)
+	s.joinIndex = 1
+
+	conf := NewClusterConfig()
+	s.doCommand(&SetClusterConfigCommand{Config: conf})
+	log.Debugf("%s sets cluster config as %v", s.Config.Name, conf)
+}
+
+func (s *PeerServer) doCommand(cmd raft.Command) {
 	for {
-		c := &JoinCommand{
-			MinVersion: store.MinVersion(),
-			MaxVersion: store.MaxVersion(),
-			Name:       s.raftServer.Name(),
-			RaftURL:    s.Config.URL,
-			EtcdURL:    s.server.URL(),
-		}
-		if _, err := s.raftServer.Do(c); err == nil {
+		if _, err := s.raftServer.Do(cmd); err == nil {
 			break
 		}
 	}
 	log.Debugf("%s start as a leader", s.Config.Name)
 }

-func (s *PeerServer) startAsFollower(cluster []string, retryTimes int) error {
+func (s *PeerServer) startAsFollower(cluster []string, retryTimes int) (bool, error) {
 	// start as a follower in a existing cluster
 	for i := 0; ; i++ {
-		ok := s.joinCluster(cluster)
-		if ok {
-			break
+		if rejected, err := s.joinCluster(cluster); rejected {
+			return true, err
+		} else if err == nil {
+			return false, nil
 		}
 		if i == retryTimes-1 {
-			return fmt.Errorf("Cannot join the cluster via given peers after %x retries", s.Config.RetryTimes)
+			break
 		}
-		log.Warnf("%v is unable to join the cluster using any of the peers %v at %dth time. Retrying in %.1f seconds", s.Config.Name, cluster, i, s.Config.RetryInterval)
+		log.Infof("%v is unable to join the cluster using any of the peers %v at %dth time. Retrying in %.1f seconds", s.Config.Name, cluster, i, s.Config.RetryInterval)
 		time.Sleep(time.Second * time.Duration(s.Config.RetryInterval))
+		continue
 	}
-
-	s.raftServer.Start()
-	return nil
+	return false, fmt.Errorf("fail joining the cluster via given peers after %x retries", retryTimes)
 }

 // Upgradable checks whether all peers in a cluster support an upgrade to the next store version.
@ -483,7 +536,7 @@ func (s *PeerServer) getKnownPeers() []string {
 	for i := range peers {
 		u, err := url.Parse(peers[i])
 		if err != nil {
-			log.Debug("getPrevPeers cannot parse url %v", peers[i])
+			log.Debugf("getKnownPeers cannot parse url %v", peers[i])
 		}
 		peers[i] = u.Host
 	}
@ -495,57 +548,55 @@ func (s *PeerServer) removeSelfFromList(peers []string) []string {
 	// Remove its own peer address from the peer list to join
 	u, err := url.Parse(s.Config.URL)
 	if err != nil {
-		log.Fatalf("removeSelfFromList cannot parse peer address %v", s.Config.URL)
+		log.Warnf("failed parsing self peer address %v", s.Config.URL)
+		u = nil
 	}
 	newPeers := make([]string, 0)
 	for _, v := range peers {
-		if v != u.Host {
+		if u == nil || v != u.Host {
 			newPeers = append(newPeers, v)
 		}
 	}
 	return newPeers
 }

-func (s *PeerServer) joinCluster(cluster []string) bool {
+func (s *PeerServer) joinCluster(cluster []string) (bool, error) {
 	for _, peer := range cluster {
 		if len(peer) == 0 {
 			continue
 		}

-		err := s.joinByPeer(s.raftServer, peer, s.Config.Scheme)
-		if err == nil {
-			log.Debugf("%s joined the cluster via peer %s", s.Config.Name, peer)
-			return true
-
+		if rejected, err := s.joinByPeer(s.raftServer, peer, s.Config.Scheme); rejected {
+			return true, fmt.Errorf("rejected by peer %s: %v", peer, err)
+		} else if err == nil {
+			log.Infof("%s joined the cluster via peer %s", s.Config.Name, peer)
+			return false, nil
+		} else {
+			log.Infof("%s attempted to join via %s failed: %v", s.Config.Name, peer, err)
 		}
-
-		if _, ok := err.(etcdErr.Error); ok {
-			log.Fatal(err)
-		}
-
-		log.Warnf("Attempt to join via %s failed: %s", peer, err)
 	}

-	return false
+	return false, fmt.Errorf("unreachable cluster")
 }

 // Send join requests to peer.
-func (s *PeerServer) joinByPeer(server raft.Server, peer string, scheme string) error {
+// The first return tells whether it is rejected by the cluster directly.
+func (s *PeerServer) joinByPeer(server raft.Server, peer string, scheme string) (bool, error) {
 	u := (&url.URL{Host: peer, Scheme: scheme}).String()

 	// Our version must match the leaders version
 	version, err := s.client.GetVersion(u)
 	if err != nil {
-		return fmt.Errorf("fail checking join version: %v", err)
+		return false, fmt.Errorf("fail checking join version: %v", err)
 	}
 	if version < store.MinVersion() || version > store.MaxVersion() {
-		return fmt.Errorf("fail passing version compatibility(%d-%d) using %d", store.MinVersion(), store.MaxVersion(), version)
+		return true, fmt.Errorf("fail passing version compatibility(%d-%d) using %d", store.MinVersion(), store.MaxVersion(), version)
 	}

 	// Fetch current peer list
 	machines, err := s.client.GetMachines(u)
 	if err != nil {
-		return fmt.Errorf("fail getting machine messages: %v", err)
+		return false, fmt.Errorf("fail getting machine messages: %v", err)
 	}
 	exist := false
 	for _, machine := range machines {
@ -558,10 +609,10 @@ func (s *PeerServer) joinByPeer(server raft.Server, peer string, scheme string)
 	// Fetch cluster config to see whether exists some place.
 	clusterConfig, err := s.client.GetClusterConfig(u)
 	if err != nil {
-		return fmt.Errorf("fail getting cluster config: %v", err)
+		return false, fmt.Errorf("fail getting cluster config: %v", err)
 	}
 	if !exist && clusterConfig.ActiveSize <= len(machines) {
-		return fmt.Errorf("stop joining because the cluster is full with %d nodes", len(machines))
+		return true, fmt.Errorf("stop joining because the cluster is full with %d nodes", len(machines))
 	}

 	joinIndex, err := s.client.AddMachine(u,
@ -573,11 +624,11 @@ func (s *PeerServer) joinByPeer(server raft.Server, peer string, scheme string)
 			EtcdURL:    s.server.URL(),
 		})
 	if err != nil {
-		return fmt.Errorf("fail on join request: %v", err)
+		return err.ErrorCode == etcdErr.EcodeNoMorePeer, fmt.Errorf("fail on join request: %v", err)
 	}

 	s.joinIndex = joinIndex
-	return nil
+	return false, nil
 }

 func (s *PeerServer) Stats() []byte {
@ -748,7 +799,7 @@ func (s *PeerServer) monitorActiveSize() {
 		// Retrieve target active size and actual active size.
 		activeSize := s.ClusterConfig().ActiveSize
 		peers := s.registry.Names()
-		peerCount := s.registry.Count()
+		peerCount := len(peers)
 		if index := sort.SearchStrings(peers, s.Config.Name); index < len(peers) && peers[index] == s.Config.Name {
 			peers = append(peers[:index], peers[index+1:]...)
 		}
@ -783,12 +834,12 @@ func (s *PeerServer) monitorPeerActivity() {

 		// Check last activity for all peers.
 		now := time.Now()
-		promoteDelay := time.Duration(s.ClusterConfig().PromoteDelay) * time.Second
+		removeDelay := time.Duration(s.ClusterConfig().RemoveDelay) * time.Second
 		peers := s.raftServer.Peers()
 		for _, peer := range peers {
 			// If the last response from the peer is longer than the promote delay
 			// then automatically demote the peer.
-			if !peer.LastActivity().IsZero() && now.Sub(peer.LastActivity()) > promoteDelay {
+			if !peer.LastActivity().IsZero() && now.Sub(peer.LastActivity()) > removeDelay {
 				log.Infof("%s: removing node: %v; last activity %v ago", s.Config.Name, peer.Name, now.Sub(peer.LastActivity()))
 				if _, err := s.raftServer.Do(&RemoveCommand{Name: peer.Name}); err != nil {
 					log.Infof("%s: warning: autodemotion error: %v", s.Config.Name, err)
--- a/server/peer_server_handlers.go
+++ b/server/peer_server_handlers.go
@ -188,7 +188,7 @@ func (ps *PeerServer) RemoveHttpHandler(w http.ResponseWriter, req *http.Request

 // Returns a JSON-encoded cluster configuration.
 func (ps *PeerServer) getClusterConfigHttpHandler(w http.ResponseWriter, req *http.Request) {
-	json.NewEncoder(w).Encode(&ps.clusterConfig)
+	json.NewEncoder(w).Encode(ps.ClusterConfig())
 }

 // Updates the cluster configuration.
@ -201,15 +201,15 @@ func (ps *PeerServer) setClusterConfigHttpHandler(w http.ResponseWriter, req *ht
 	}

 	// Copy config and update fields passed in.
-	config := &ClusterConfig{
-		ActiveSize:   ps.clusterConfig.ActiveSize,
-		PromoteDelay: ps.clusterConfig.PromoteDelay,
-	}
+	config := ps.ClusterConfig()
 	if activeSize, ok := m["activeSize"].(float64); ok {
 		config.ActiveSize = int(activeSize)
 	}
-	if promoteDelay, ok := m["promoteDelay"].(float64); ok {
-		config.PromoteDelay = int(promoteDelay)
+	if removeDelay, ok := m["removeDelay"].(float64); ok {
+		config.RemoveDelay = int(removeDelay)
+	}
+	if syncClusterInterval, ok := m["syncClusterInterval"].(float64); ok {
+		config.SyncClusterInterval = int(syncClusterInterval)
 	}

 	// Issue command to update.
@ -217,10 +217,11 @@ func (ps *PeerServer) setClusterConfigHttpHandler(w http.ResponseWriter, req *ht
 	log.Debugf("[recv] Update Cluster Config Request")
 	ps.server.Dispatch(c, w, req)

-	json.NewEncoder(w).Encode(&ps.clusterConfig)
+	json.NewEncoder(w).Encode(ps.ClusterConfig())
 }

 // Retrieves a list of peers and standbys.
+// If leader exists, it is at the first place.
 func (ps *PeerServer) getMachinesHttpHandler(w http.ResponseWriter, req *http.Request) {
 	machines := make([]*machineMessage, 0)
 	leader := ps.raftServer.Leader()
@ -229,6 +230,7 @@ func (ps *PeerServer) getMachinesHttpHandler(w http.ResponseWriter, req *http.Re
 			machines = append(machines, msg)
 		}
 	}
+
 	json.NewEncoder(w).Encode(&machines)
 }

--- a/server/remove_command.go
+++ b/server/remove_command.go
@ -68,6 +68,7 @@ func applyRemove(c *RemoveCommand, context raft.Context) (uint64, error) {
 		} else {
 			// else ignore remove
 			log.Debugf("ignore previous remove command.")
+			ps.removedInLog = true
 		}
 	}
 	return commitIndex, nil
--- a/server/standby_server.go
+++ b/server/standby_server.go
@ -0,0 +1,256 @@
+package server
+
+import (
+	"fmt"
+	"net/http"
+	"net/url"
+	"sync"
+	"time"
+
+	"github.com/coreos/etcd/third_party/github.com/goraft/raft"
+
+	etcdErr "github.com/coreos/etcd/error"
+	"github.com/coreos/etcd/log"
+	uhttp "github.com/coreos/etcd/pkg/http"
+	"github.com/coreos/etcd/store"
+)
+
+const UninitedSyncClusterInterval = time.Duration(5) * time.Second
+
+type StandbyServerConfig struct {
+	Name       string
+	PeerScheme string
+	PeerURL    string
+	ClientURL  string
+}
+
+type StandbyServer struct {
+	Config StandbyServerConfig
+	client *Client
+
+	cluster             []*machineMessage
+	syncClusterInterval time.Duration
+	joinIndex           uint64
+
+	removeNotify chan bool
+	started      bool
+	closeChan    chan bool
+	routineGroup sync.WaitGroup
+
+	sync.Mutex
+}
+
+func NewStandbyServer(config StandbyServerConfig, client *Client) *StandbyServer {
+	return &StandbyServer{
+		Config:              config,
+		client:              client,
+		syncClusterInterval: UninitedSyncClusterInterval,
+	}
+}
+
+func (s *StandbyServer) Start() {
+	s.Lock()
+	defer s.Unlock()
+	if s.started {
+		return
+	}
+	s.started = true
+
+	s.removeNotify = make(chan bool)
+	s.closeChan = make(chan bool)
+
+	s.routineGroup.Add(1)
+	go func() {
+		defer s.routineGroup.Done()
+		s.monitorCluster()
+	}()
+}
+
+// Stop stops the server gracefully.
+func (s *StandbyServer) Stop() {
+	s.Lock()
+	defer s.Unlock()
+	if !s.started {
+		return
+	}
+	s.started = false
+
+	close(s.closeChan)
+	s.routineGroup.Wait()
+}
+
+// RemoveNotify notifies the server is removed from standby mode and ready
+// for peer mode. It should have joined the cluster successfully.
+func (s *StandbyServer) RemoveNotify() <-chan bool {
+	return s.removeNotify
+}
+
+func (s *StandbyServer) ClientHTTPHandler() http.Handler {
+	return http.HandlerFunc(s.redirectRequests)
+}
+
+func (s *StandbyServer) Cluster() []string {
+	peerURLs := make([]string, 0)
+	for _, peer := range s.cluster {
+		peerURLs = append(peerURLs, peer.PeerURL)
+	}
+	return peerURLs
+}
+
+func (s *StandbyServer) ClusterSize() int {
+	return len(s.cluster)
+}
+
+func (s *StandbyServer) setCluster(cluster []*machineMessage) {
+	s.cluster = cluster
+}
+
+func (s *StandbyServer) SyncCluster(peers []string) error {
+	for i, url := range peers {
+		peers[i] = s.fullPeerURL(url)
+	}
+
+	if err := s.syncCluster(peers); err != nil {
+		log.Infof("fail syncing cluster(%v): %v", s.Cluster(), err)
+		return err
+	}
+
+	log.Infof("set cluster(%v) for standby server", s.Cluster())
+	return nil
+}
+
+func (s *StandbyServer) SetSyncClusterInterval(second int) {
+	s.syncClusterInterval = time.Duration(second) * time.Second
+}
+
+func (s *StandbyServer) ClusterLeader() *machineMessage {
+	for _, machine := range s.cluster {
+		if machine.State == raft.Leader {
+			return machine
+		}
+	}
+	return nil
+}
+
+func (s *StandbyServer) JoinIndex() uint64 {
+	return s.joinIndex
+}
+
+func (s *StandbyServer) redirectRequests(w http.ResponseWriter, r *http.Request) {
+	leader := s.ClusterLeader()
+	if leader == nil {
+		w.Header().Set("Content-Type", "application/json")
+		etcdErr.NewError(etcdErr.EcodeStandbyInternal, "", 0).Write(w)
+		return
+	}
+	uhttp.Redirect(leader.ClientURL, w, r)
+}
+
+func (s *StandbyServer) monitorCluster() {
+	for {
+		timer := time.NewTimer(s.syncClusterInterval)
+		defer timer.Stop()
+		select {
+		case <-s.closeChan:
+			return
+		case <-timer.C:
+		}
+
+		if err := s.syncCluster(nil); err != nil {
+			log.Warnf("fail syncing cluster(%v): %v", s.Cluster(), err)
+			continue
+		}
+
+		leader := s.ClusterLeader()
+		if leader == nil {
+			log.Warnf("fail getting leader from cluster(%v)", s.Cluster())
+			continue
+		}
+
+		if err := s.join(leader.PeerURL); err != nil {
+			log.Debugf("fail joining through leader %v: %v", leader, err)
+			continue
+		}
+
+		log.Infof("join through leader %v", leader.PeerURL)
+		go func() {
+			s.Stop()
+			close(s.removeNotify)
+		}()
+		return
+	}
+}
+
+func (s *StandbyServer) syncCluster(peerURLs []string) error {
+	peerURLs = append(s.Cluster(), peerURLs...)
+
+	for _, peerURL := range peerURLs {
+		// Fetch current peer list
+		machines, err := s.client.GetMachines(peerURL)
+		if err != nil {
+			log.Debugf("fail getting machine messages from %v", peerURL)
+			continue
+		}
+
+		config, err := s.client.GetClusterConfig(peerURL)
+		if err != nil {
+			log.Debugf("fail getting cluster config from %v", peerURL)
+			continue
+		}
+
+		s.setCluster(machines)
+		s.SetSyncClusterInterval(config.SyncClusterInterval)
+		return nil
+	}
+	return fmt.Errorf("unreachable cluster")
+}
+
+func (s *StandbyServer) join(peer string) error {
+	// Our version must match the leaders version
+	version, err := s.client.GetVersion(peer)
+	if err != nil {
+		log.Debugf("fail checking join version")
+		return err
+	}
+	if version < store.MinVersion() || version > store.MaxVersion() {
+		log.Debugf("fail passing version compatibility(%d-%d) using %d", store.MinVersion(), store.MaxVersion(), version)
+		return fmt.Errorf("incompatible version")
+	}
+
+	// Fetch cluster config to see whether exists some place.
+	clusterConfig, err := s.client.GetClusterConfig(peer)
+	if err != nil {
+		log.Debugf("fail getting cluster config")
+		return err
+	}
+	if clusterConfig.ActiveSize <= len(s.Cluster()) {
+		log.Debugf("stop joining because the cluster is full with %d nodes", len(s.Cluster()))
+		return fmt.Errorf("out of quota")
+	}
+
+	commitIndex, err := s.client.AddMachine(peer,
+		&JoinCommand{
+			MinVersion: store.MinVersion(),
+			MaxVersion: store.MaxVersion(),
+			Name:       s.Config.Name,
+			RaftURL:    s.Config.PeerURL,
+			EtcdURL:    s.Config.ClientURL,
+		})
+	if err != nil {
+		log.Debugf("fail on join request")
+		return err
+	}
+	s.joinIndex = commitIndex
+
+	return nil
+}
+
+func (s *StandbyServer) fullPeerURL(urlStr string) string {
+	u, err := url.Parse(urlStr)
+	if err != nil {
+		log.Warnf("fail parsing url %v", u)
+		return urlStr
+	}
+	u.Scheme = s.Config.PeerScheme
+	return u.String()
+}
--- a/server/v1/tests/delete_handler_test.go
+++ b/server/v1/tests/delete_handler_test.go
@ -26,6 +26,6 @@ func TestV1DeleteKey(t *testing.T) {
 		assert.Equal(t, resp.StatusCode, http.StatusOK)
 		body := tests.ReadBody(resp)
 		assert.Nil(t, err, "")
-		assert.Equal(t, string(body), `{"action":"delete","key":"/foo/bar","prevValue":"XXX","index":3}`, "")
+		assert.Equal(t, string(body), `{"action":"delete","key":"/foo/bar","prevValue":"XXX","index":4}`, "")
 	})
 }
--- a/server/v1/tests/get_handler_test.go
+++ b/server/v1/tests/get_handler_test.go
@ -36,7 +36,7 @@ func TestV1GetKey(t *testing.T) {
 		assert.Equal(t, body["action"], "get", "")
 		assert.Equal(t, body["key"], "/foo/bar", "")
 		assert.Equal(t, body["value"], "XXX", "")
-		assert.Equal(t, body["index"], 2, "")
+		assert.Equal(t, body["index"], 3, "")
 	})
 }

@ -117,7 +117,7 @@ func TestV1WatchKey(t *testing.T) {

 		assert.Equal(t, body["key"], "/foo/bar", "")
 		assert.Equal(t, body["value"], "XXX", "")
-		assert.Equal(t, body["index"], 2, "")
+		assert.Equal(t, body["index"], 3, "")
 	})
 }

@ -133,7 +133,7 @@ func TestV1WatchKeyWithIndex(t *testing.T) {
 		c := make(chan bool)
 		go func() {
 			v := url.Values{}
-			v.Set("index", "3")
+			v.Set("index", "4")
 			resp, _ := tests.PostForm(fmt.Sprintf("%s%s", s.URL(), "/v1/watch/foo/bar"), v)
 			body = tests.ReadBodyJSON(resp)
 			c <- true
@ -173,7 +173,7 @@ func TestV1WatchKeyWithIndex(t *testing.T) {

 		assert.Equal(t, body["key"], "/foo/bar", "")
 		assert.Equal(t, body["value"], "YYY", "")
-		assert.Equal(t, body["index"], 3, "")
+		assert.Equal(t, body["index"], 4, "")
 	})
 }

--- a/server/v1/tests/put_handler_test.go
+++ b/server/v1/tests/put_handler_test.go
@ -25,7 +25,7 @@ func TestV1SetKey(t *testing.T) {
 		body := tests.ReadBody(resp)
 		assert.Nil(t, err, "")

-		assert.Equal(t, string(body), `{"action":"set","key":"/foo/bar","value":"XXX","newKey":true,"index":2}`, "")
+		assert.Equal(t, string(body), `{"action":"set","key":"/foo/bar","value":"XXX","newKey":true,"index":3}`, "")
 	})
 }

@ -127,7 +127,7 @@ func TestV1SetKeyCASOnValueSuccess(t *testing.T) {
 		body := tests.ReadBodyJSON(resp)
 		assert.Equal(t, body["action"], "testAndSet", "")
 		assert.Equal(t, body["value"], "YYY", "")
-		assert.Equal(t, body["index"], 3, "")
+		assert.Equal(t, body["index"], 4, "")
 	})
 }

@ -152,6 +152,6 @@ func TestV1SetKeyCASOnValueFail(t *testing.T) {
 		assert.Equal(t, body["errorCode"], 101, "")
 		assert.Equal(t, body["message"], "Compare failed", "")
 		assert.Equal(t, body["cause"], "[AAA != XXX]", "")
-		assert.Equal(t, body["index"], 2, "")
+		assert.Equal(t, body["index"], 3, "")
 	})
 }
--- a/server/v2/tests/delete_handler_test.go
+++ b/server/v2/tests/delete_handler_test.go
@ -26,7 +26,7 @@ func TestV2DeleteKey(t *testing.T) {
 		assert.Equal(t, resp.StatusCode, http.StatusOK)
 		body := tests.ReadBody(resp)
 		assert.Nil(t, err, "")
-		assert.Equal(t, string(body), `{"action":"delete","node":{"key":"/foo/bar","modifiedIndex":3,"createdIndex":2},"prevNode":{"key":"/foo/bar","value":"XXX","modifiedIndex":2,"createdIndex":2}}`, "")
+		assert.Equal(t, string(body), `{"action":"delete","node":{"key":"/foo/bar","modifiedIndex":4,"createdIndex":3},"prevNode":{"key":"/foo/bar","value":"XXX","modifiedIndex":3,"createdIndex":3}}`, "")
 	})
 }

@ -48,7 +48,7 @@ func TestV2DeleteEmptyDirectory(t *testing.T) {
 		assert.Equal(t, resp.StatusCode, http.StatusOK)
 		body := tests.ReadBody(resp)
 		assert.Nil(t, err, "")
-		assert.Equal(t, string(body), `{"action":"delete","node":{"key":"/foo","dir":true,"modifiedIndex":3,"createdIndex":2},"prevNode":{"key":"/foo","dir":true,"modifiedIndex":2,"createdIndex":2}}`, "")
+		assert.Equal(t, string(body), `{"action":"delete","node":{"key":"/foo","dir":true,"modifiedIndex":4,"createdIndex":3},"prevNode":{"key":"/foo","dir":true,"modifiedIndex":3,"createdIndex":3}}`, "")
 	})
 }

@ -70,7 +70,7 @@ func TestV2DeleteNonEmptyDirectory(t *testing.T) {
 		assert.Equal(t, resp.StatusCode, http.StatusOK)
 		body := tests.ReadBody(resp)
 		assert.Nil(t, err, "")
-		assert.Equal(t, string(body), `{"action":"delete","node":{"key":"/foo","dir":true,"modifiedIndex":3,"createdIndex":2},"prevNode":{"key":"/foo","dir":true,"modifiedIndex":2,"createdIndex":2}}`, "")
+		assert.Equal(t, string(body), `{"action":"delete","node":{"key":"/foo","dir":true,"modifiedIndex":4,"createdIndex":3},"prevNode":{"key":"/foo","dir":true,"modifiedIndex":3,"createdIndex":3}}`, "")
 	})
 }

@ -87,14 +87,14 @@ func TestV2DeleteDirectoryRecursiveImpliesDir(t *testing.T) {
 		assert.Equal(t, resp.StatusCode, http.StatusOK)
 		body := tests.ReadBody(resp)
 		assert.Nil(t, err, "")
-		assert.Equal(t, string(body), `{"action":"delete","node":{"key":"/foo","dir":true,"modifiedIndex":3,"createdIndex":2},"prevNode":{"key":"/foo","dir":true,"modifiedIndex":2,"createdIndex":2}}`, "")
+		assert.Equal(t, string(body), `{"action":"delete","node":{"key":"/foo","dir":true,"modifiedIndex":4,"createdIndex":3},"prevNode":{"key":"/foo","dir":true,"modifiedIndex":3,"createdIndex":3}}`, "")
 	})
 }

 // Ensures that a key is deleted if the previous index matches
 //
 //   $ curl -X PUT localhost:4001/v2/keys/foo -d value=XXX
-//   $ curl -X DELETE localhost:4001/v2/keys/foo?prevIndex=2
+//   $ curl -X DELETE localhost:4001/v2/keys/foo?prevIndex=3
 //
 func TestV2DeleteKeyCADOnIndexSuccess(t *testing.T) {
 	tests.RunServer(func(s *server.Server) {
@ -102,14 +102,14 @@ func TestV2DeleteKeyCADOnIndexSuccess(t *testing.T) {
 		v.Set("value", "XXX")
 		resp, err := tests.PutForm(fmt.Sprintf("%s%s", s.URL(), "/v2/keys/foo"), v)
 		tests.ReadBody(resp)
-		resp, err = tests.DeleteForm(fmt.Sprintf("%s%s", s.URL(), "/v2/keys/foo?prevIndex=2"), url.Values{})
+		resp, err = tests.DeleteForm(fmt.Sprintf("%s%s", s.URL(), "/v2/keys/foo?prevIndex=3"), url.Values{})
 		assert.Nil(t, err, "")
 		body := tests.ReadBodyJSON(resp)
 		assert.Equal(t, body["action"], "compareAndDelete", "")

 		node := body["node"].(map[string]interface{})
 		assert.Equal(t, node["key"], "/foo", "")
-		assert.Equal(t, node["modifiedIndex"], 3, "")
+		assert.Equal(t, node["modifiedIndex"], 4, "")
 	})
 }

@ -164,7 +164,7 @@ func TestV2DeleteKeyCADOnValueSuccess(t *testing.T) {
 		assert.Equal(t, body["action"], "compareAndDelete", "")

 		node := body["node"].(map[string]interface{})
-		assert.Equal(t, node["modifiedIndex"], 3, "")
+		assert.Equal(t, node["modifiedIndex"], 4, "")
 	})
 }

--- a/server/v2/tests/get_handler_test.go
+++ b/server/v2/tests/get_handler_test.go
@ -36,7 +36,7 @@ func TestV2GetKey(t *testing.T) {
 		node := body["node"].(map[string]interface{})
 		assert.Equal(t, node["key"], "/foo/bar", "")
 		assert.Equal(t, node["value"], "XXX", "")
-		assert.Equal(t, node["modifiedIndex"], 2, "")
+		assert.Equal(t, node["modifiedIndex"], 3, "")
 	})
 }

@ -65,7 +65,7 @@ func TestV2GetKeyRecursively(t *testing.T) {
 		node := body["node"].(map[string]interface{})
 		assert.Equal(t, node["key"], "/foo", "")
 		assert.Equal(t, node["dir"], true, "")
-		assert.Equal(t, node["modifiedIndex"], 2, "")
+		assert.Equal(t, node["modifiedIndex"], 3, "")
 		assert.Equal(t, len(node["nodes"].([]interface{})), 2, "")

 		node0 := node["nodes"].([]interface{})[0].(map[string]interface{})
@ -130,7 +130,7 @@ func TestV2WatchKey(t *testing.T) {
 		node := body["node"].(map[string]interface{})
 		assert.Equal(t, node["key"], "/foo/bar", "")
 		assert.Equal(t, node["value"], "XXX", "")
-		assert.Equal(t, node["modifiedIndex"], 2, "")
+		assert.Equal(t, node["modifiedIndex"], 3, "")
 	})
 }

@ -145,7 +145,7 @@ func TestV2WatchKeyWithIndex(t *testing.T) {
 		var body map[string]interface{}
 		c := make(chan bool)
 		go func() {
-			resp, _ := tests.Get(fmt.Sprintf("%s%s", s.URL(), "/v2/keys/foo/bar?wait=true&waitIndex=3"))
+			resp, _ := tests.Get(fmt.Sprintf("%s%s", s.URL(), "/v2/keys/foo/bar?wait=true&waitIndex=4"))
 			body = tests.ReadBodyJSON(resp)
 			c <- true
 		}()
@ -185,7 +185,7 @@ func TestV2WatchKeyWithIndex(t *testing.T) {
 		node := body["node"].(map[string]interface{})
 		assert.Equal(t, node["key"], "/foo/bar", "")
 		assert.Equal(t, node["value"], "YYY", "")
-		assert.Equal(t, node["modifiedIndex"], 3, "")
+		assert.Equal(t, node["modifiedIndex"], 4, "")
 	})
 }

--- a/server/v2/tests/post_handler_test.go
+++ b/server/v2/tests/post_handler_test.go
@ -26,9 +26,9 @@ func TestV2CreateUnique(t *testing.T) {
 		assert.Equal(t, body["action"], "create", "")

 		node := body["node"].(map[string]interface{})
-		assert.Equal(t, node["key"], "/foo/bar/2", "")
+		assert.Equal(t, node["key"], "/foo/bar/3", "")
 		assert.Nil(t, node["dir"], "")
-		assert.Equal(t, node["modifiedIndex"], 2, "")
+		assert.Equal(t, node["modifiedIndex"], 3, "")

 		// Second POST should add next index to list.
 		resp, _ = tests.PostForm(fullURL, nil)
@ -36,7 +36,7 @@ func TestV2CreateUnique(t *testing.T) {
 		body = tests.ReadBodyJSON(resp)

 		node = body["node"].(map[string]interface{})
-		assert.Equal(t, node["key"], "/foo/bar/3", "")
+		assert.Equal(t, node["key"], "/foo/bar/4", "")

 		// POST to a different key should add index to that list.
 		resp, _ = tests.PostForm(fmt.Sprintf("%s%s", s.URL(), "/v2/keys/foo/baz"), nil)
@ -44,6 +44,6 @@ func TestV2CreateUnique(t *testing.T) {
 		body = tests.ReadBodyJSON(resp)

 		node = body["node"].(map[string]interface{})
-		assert.Equal(t, node["key"], "/foo/baz/4", "")
+		assert.Equal(t, node["key"], "/foo/baz/5", "")
 	})
 }
--- a/server/v2/tests/put_handler_test.go
+++ b/server/v2/tests/put_handler_test.go
@ -24,7 +24,7 @@ func TestV2SetKey(t *testing.T) {
 		assert.Equal(t, resp.StatusCode, http.StatusCreated)
 		body := tests.ReadBody(resp)
 		assert.Nil(t, err, "")
-		assert.Equal(t, string(body), `{"action":"set","node":{"key":"/foo/bar","value":"XXX","modifiedIndex":2,"createdIndex":2}}`, "")
+		assert.Equal(t, string(body), `{"action":"set","node":{"key":"/foo/bar","value":"XXX","modifiedIndex":3,"createdIndex":3}}`, "")
 	})
 }

@ -38,7 +38,7 @@ func TestV2SetDirectory(t *testing.T) {
 		assert.Equal(t, resp.StatusCode, http.StatusCreated)
 		body := tests.ReadBody(resp)
 		assert.Nil(t, err, "")
-		assert.Equal(t, string(body), `{"action":"set","node":{"key":"/foo","dir":true,"modifiedIndex":2,"createdIndex":2}}`, "")
+		assert.Equal(t, string(body), `{"action":"set","node":{"key":"/foo","dir":true,"modifiedIndex":3,"createdIndex":3}}`, "")
 	})
 }

@ -244,14 +244,14 @@ func TestV2SetKeyCASOnIndexSuccess(t *testing.T) {
 		assert.Equal(t, resp.StatusCode, http.StatusCreated)
 		tests.ReadBody(resp)
 		v.Set("value", "YYY")
-		v.Set("prevIndex", "2")
+		v.Set("prevIndex", "3")
 		resp, _ = tests.PutForm(fullURL, v)
 		assert.Equal(t, resp.StatusCode, http.StatusOK)
 		body := tests.ReadBodyJSON(resp)
 		assert.Equal(t, body["action"], "compareAndSwap", "")
 		node := body["node"].(map[string]interface{})
 		assert.Equal(t, node["value"], "YYY", "")
-		assert.Equal(t, node["modifiedIndex"], 3, "")
+		assert.Equal(t, node["modifiedIndex"], 4, "")
 	})
 }

@ -275,8 +275,8 @@ func TestV2SetKeyCASOnIndexFail(t *testing.T) {
 		body := tests.ReadBodyJSON(resp)
 		assert.Equal(t, body["errorCode"], 101, "")
 		assert.Equal(t, body["message"], "Compare failed", "")
-		assert.Equal(t, body["cause"], "[10 != 2]", "")
-		assert.Equal(t, body["index"], 2, "")
+		assert.Equal(t, body["cause"], "[10 != 3]", "")
+		assert.Equal(t, body["index"], 3, "")
 	})
 }

@ -319,7 +319,7 @@ func TestV2SetKeyCASOnValueSuccess(t *testing.T) {
 		assert.Equal(t, body["action"], "compareAndSwap", "")
 		node := body["node"].(map[string]interface{})
 		assert.Equal(t, node["value"], "YYY", "")
-		assert.Equal(t, node["modifiedIndex"], 3, "")
+		assert.Equal(t, node["modifiedIndex"], 4, "")
 	})
 }

@ -344,7 +344,7 @@ func TestV2SetKeyCASOnValueFail(t *testing.T) {
 		assert.Equal(t, body["errorCode"], 101, "")
 		assert.Equal(t, body["message"], "Compare failed", "")
 		assert.Equal(t, body["cause"], "[AAA != XXX]", "")
-		assert.Equal(t, body["index"], 2, "")
+		assert.Equal(t, body["index"], 3, "")
 	})
 }

@ -369,7 +369,7 @@ func TestV2SetKeyCASWithMissingValueFails(t *testing.T) {
 // Ensures that a key is not set if both previous value and index do not match.
 //
 //   $ curl -X PUT localhost:4001/v2/keys/foo/bar -d value=XXX
-//   $ curl -X PUT localhost:4001/v2/keys/foo/bar -d value=YYY -d prevValue=AAA -d prevIndex=3
+//   $ curl -X PUT localhost:4001/v2/keys/foo/bar -d value=YYY -d prevValue=AAA -d prevIndex=4
 //
 func TestV2SetKeyCASOnValueAndIndexFail(t *testing.T) {
 	tests.RunServer(func(s *server.Server) {
@ -381,21 +381,21 @@ func TestV2SetKeyCASOnValueAndIndexFail(t *testing.T) {
 		tests.ReadBody(resp)
 		v.Set("value", "YYY")
 		v.Set("prevValue", "AAA")
-		v.Set("prevIndex", "3")
+		v.Set("prevIndex", "4")
 		resp, _ = tests.PutForm(fullURL, v)
 		assert.Equal(t, resp.StatusCode, http.StatusPreconditionFailed)
 		body := tests.ReadBodyJSON(resp)
 		assert.Equal(t, body["errorCode"], 101, "")
 		assert.Equal(t, body["message"], "Compare failed", "")
-		assert.Equal(t, body["cause"], "[AAA != XXX] [3 != 2]", "")
-		assert.Equal(t, body["index"], 2, "")
+		assert.Equal(t, body["cause"], "[AAA != XXX] [4 != 3]", "")
+		assert.Equal(t, body["index"], 3, "")
 	})
 }

 // Ensures that a key is not set if previous value match but index does not.
 //
 //   $ curl -X PUT localhost:4001/v2/keys/foo/bar -d value=XXX
-//   $ curl -X PUT localhost:4001/v2/keys/foo/bar -d value=YYY -d prevValue=XXX -d prevIndex=3
+//   $ curl -X PUT localhost:4001/v2/keys/foo/bar -d value=YYY -d prevValue=XXX -d prevIndex=4
 //
 func TestV2SetKeyCASOnValueMatchAndIndexFail(t *testing.T) {
 	tests.RunServer(func(s *server.Server) {
@ -407,21 +407,21 @@ func TestV2SetKeyCASOnValueMatchAndIndexFail(t *testing.T) {
 		tests.ReadBody(resp)
 		v.Set("value", "YYY")
 		v.Set("prevValue", "XXX")
-		v.Set("prevIndex", "3")
+		v.Set("prevIndex", "4")
 		resp, _ = tests.PutForm(fullURL, v)
 		assert.Equal(t, resp.StatusCode, http.StatusPreconditionFailed)
 		body := tests.ReadBodyJSON(resp)
 		assert.Equal(t, body["errorCode"], 101, "")
 		assert.Equal(t, body["message"], "Compare failed", "")
-		assert.Equal(t, body["cause"], "[3 != 2]", "")
-		assert.Equal(t, body["index"], 2, "")
+		assert.Equal(t, body["cause"], "[4 != 3]", "")
+		assert.Equal(t, body["index"], 3, "")
 	})
 }

 // Ensures that a key is not set if previous index matches but value does not.
 //
 //   $ curl -X PUT localhost:4001/v2/keys/foo/bar -d value=XXX
-//   $ curl -X PUT localhost:4001/v2/keys/foo/bar -d value=YYY -d prevValue=AAA -d prevIndex=2
+//   $ curl -X PUT localhost:4001/v2/keys/foo/bar -d value=YYY -d prevValue=AAA -d prevIndex=3
 //
 func TestV2SetKeyCASOnIndexMatchAndValueFail(t *testing.T) {
 	tests.RunServer(func(s *server.Server) {
@ -433,14 +433,14 @@ func TestV2SetKeyCASOnIndexMatchAndValueFail(t *testing.T) {
 		tests.ReadBody(resp)
 		v.Set("value", "YYY")
 		v.Set("prevValue", "AAA")
-		v.Set("prevIndex", "2")
+		v.Set("prevIndex", "3")
 		resp, _ = tests.PutForm(fullURL, v)
 		assert.Equal(t, resp.StatusCode, http.StatusPreconditionFailed)
 		body := tests.ReadBodyJSON(resp)
 		assert.Equal(t, body["errorCode"], 101, "")
 		assert.Equal(t, body["message"], "Compare failed", "")
 		assert.Equal(t, body["cause"], "[AAA != XXX]", "")
-		assert.Equal(t, body["index"], 2, "")
+		assert.Equal(t, body["index"], 3, "")
 	})
 }

@ -455,6 +455,6 @@ func TestV2SetKeyCASWithEmptyValueSuccess(t *testing.T) {
 		resp, _ := tests.PutForm(fmt.Sprintf("%s%s", s.URL(), "/v2/keys/foo/bar"), v)
 		assert.Equal(t, resp.StatusCode, http.StatusCreated)
 		body := tests.ReadBody(resp)
-		assert.Equal(t, string(body), `{"action":"set","node":{"key":"/foo/bar","value":"","modifiedIndex":2,"createdIndex":2}}`)
+		assert.Equal(t, string(body), `{"action":"set","node":{"key":"/foo/bar","value":"","modifiedIndex":3,"createdIndex":3}}`)
 	})
 }
--- a/tests/functional/cluster_config_test.go
+++ b/tests/functional/cluster_config_test.go
@ -12,12 +12,12 @@ import (
 )

 // Ensure that the cluster configuration can be updated.
-func TestClusterConfig(t *testing.T) {
+func TestClusterConfigSet(t *testing.T) {
 	_, etcds, err := CreateCluster(3, &os.ProcAttr{Files: []*os.File{nil, os.Stdout, os.Stderr}}, false)
 	assert.NoError(t, err)
 	defer DestroyCluster(etcds)

-	resp, _ := tests.Put("http://localhost:7001/v2/admin/config", "application/json", bytes.NewBufferString(`{"activeSize":3, "promoteDelay":60}`))
+	resp, _ := tests.Put("http://localhost:7001/v2/admin/config", "application/json", bytes.NewBufferString(`{"activeSize":3, "removeDelay":60}`))
 	assert.Equal(t, resp.StatusCode, 200)

 	time.Sleep(1 * time.Second)
@ -26,7 +26,41 @@ func TestClusterConfig(t *testing.T) {
 	body := tests.ReadBodyJSON(resp)
 	assert.Equal(t, resp.StatusCode, 200)
 	assert.Equal(t, body["activeSize"], 3)
-	assert.Equal(t, body["promoteDelay"], 60)
+	assert.Equal(t, body["removeDelay"], 60)
+}
+
+// Ensure that the cluster configuration can be reloaded.
+func TestClusterConfigReload(t *testing.T) {
+	procAttr := &os.ProcAttr{Files: []*os.File{nil, os.Stdout, os.Stderr}}
+	argGroup, etcds, err := CreateCluster(3, procAttr, false)
+	assert.NoError(t, err)
+	defer DestroyCluster(etcds)
+
+	resp, _ := tests.Put("http://localhost:7001/v2/admin/config", "application/json", bytes.NewBufferString(`{"activeSize":3, "removeDelay":60}`))
+	assert.Equal(t, resp.StatusCode, 200)
+
+	time.Sleep(1 * time.Second)
+
+	resp, _ = tests.Get("http://localhost:7002/v2/admin/config")
+	body := tests.ReadBodyJSON(resp)
+	assert.Equal(t, resp.StatusCode, 200)
+	assert.Equal(t, body["activeSize"], 3)
+	assert.Equal(t, body["removeDelay"], 60)
+
+	// kill all
+	DestroyCluster(etcds)
+
+	for i := 0; i < 3; i++ {
+		etcds[i], err = os.StartProcess(EtcdBinPath, argGroup[i], procAttr)
+	}
+
+	time.Sleep(1 * time.Second)
+
+	resp, _ = tests.Get("http://localhost:7002/v2/admin/config")
+	body = tests.ReadBodyJSON(resp)
+	assert.Equal(t, resp.StatusCode, 200)
+	assert.Equal(t, body["activeSize"], 3)
+	assert.Equal(t, body["removeDelay"], 60)
 }

 // TestGetMachines tests '/v2/admin/machines' sends back messages of all machines.
--- a/tests/functional/kill_leader_test.go
+++ b/tests/functional/kill_leader_test.go
@ -1,12 +1,18 @@
 package test

 import (
+	"bytes"
 	"fmt"
 	"os"
 	"strconv"
 	"strings"
 	"testing"
 	"time"
+
+	"github.com/coreos/etcd/server"
+	"github.com/coreos/etcd/tests"
+	"github.com/coreos/etcd/third_party/github.com/coreos/go-etcd/etcd"
+	"github.com/coreos/etcd/third_party/github.com/stretchr/testify/assert"
 )

 // This test will kill the current leader and wait for the etcd cluster to elect a new leader for 200 times.
@ -15,7 +21,7 @@ func TestKillLeader(t *testing.T) {
 	procAttr := new(os.ProcAttr)
 	procAttr.Files = []*os.File{nil, os.Stdout, os.Stderr}

-	clusterSize := 5
+	clusterSize := 3
 	argGroup, etcds, err := CreateCluster(clusterSize, procAttr, false)
 	if err != nil {
 		t.Fatal("cannot create cluster")
@ -60,3 +66,88 @@ func TestKillLeader(t *testing.T) {
 	}
 	stop <- true
 }
+
+// This test will kill the current leader and wait for the etcd cluster to elect a new leader for 200 times.
+// It will print out the election time and the average election time.
+// It runs in a cluster with standby nodes.
+func TestKillLeaderWithStandbys(t *testing.T) {
+	// https://github.com/goraft/raft/issues/222
+	t.Skip("stuck on raft issue")
+
+	procAttr := new(os.ProcAttr)
+	procAttr.Files = []*os.File{nil, os.Stdout, os.Stderr}
+
+	clusterSize := 5
+	argGroup, etcds, err := CreateCluster(clusterSize, procAttr, false)
+	if err != nil {
+		t.Fatal("cannot create cluster")
+	}
+	defer DestroyCluster(etcds)
+
+	stop := make(chan bool)
+	leaderChan := make(chan string, 1)
+	all := make(chan bool, 1)
+
+	time.Sleep(time.Second)
+
+	go Monitor(clusterSize, 1, leaderChan, all, stop)
+
+	c := etcd.NewClient(nil)
+	c.SyncCluster()
+
+	// Reconfigure with a small active size.
+	resp, _ := tests.Put("http://localhost:7001/v2/admin/config", "application/json", bytes.NewBufferString(`{"activeSize":3, "removeDelay":2, "syncClusterInterval":1}`))
+	if !assert.Equal(t, resp.StatusCode, 200) {
+		t.FailNow()
+	}
+
+	// Wait for two monitor cycles before checking for demotion.
+	time.Sleep((2 * server.ActiveMonitorTimeout) + (2 * time.Second))
+
+	// Verify that we have 3 peers.
+	result, err := c.Get("_etcd/machines", true, true)
+	assert.NoError(t, err)
+	assert.Equal(t, len(result.Node.Nodes), 3)
+
+	var totalTime time.Duration
+
+	leader := "http://127.0.0.1:7001"
+
+	for i := 0; i < clusterSize; i++ {
+		fmt.Println("leader is ", leader)
+		port, _ := strconv.Atoi(strings.Split(leader, ":")[2])
+		num := port - 7001
+		fmt.Println("kill server ", num)
+		etcds[num].Kill()
+		etcds[num].Release()
+
+		start := time.Now()
+		for {
+			newLeader := <-leaderChan
+			if newLeader != leader {
+				leader = newLeader
+				break
+			}
+		}
+		take := time.Now().Sub(start)
+
+		totalTime += take
+		avgTime := totalTime / (time.Duration)(i+1)
+		fmt.Println("Total time:", totalTime, "; Avg time:", avgTime)
+
+		time.Sleep(server.ActiveMonitorTimeout + (1 * time.Second))
+		time.Sleep(2 * time.Second)
+
+		// Verify that we have 3 peers.
+		result, err = c.Get("_etcd/machines", true, true)
+		assert.NoError(t, err)
+		assert.Equal(t, len(result.Node.Nodes), 3)
+
+		// Verify that killed node is not one of those peers.
+		_, err = c.Get(fmt.Sprintf("_etcd/machines/node%d", num+1), false, false)
+		assert.Error(t, err)
+
+		etcds[num], err = os.StartProcess(EtcdBinPath, argGroup[num], procAttr)
+	}
+	stop <- true
+}
--- a/tests/functional/multi_node_kill_all_and_recovery_test.go
+++ b/tests/functional/multi_node_kill_all_and_recovery_test.go
@ -1,12 +1,16 @@
 package test

 import (
+	"bytes"
 	"os"
 	"strconv"
 	"testing"
 	"time"

+	"github.com/coreos/etcd/server"
+	"github.com/coreos/etcd/tests"
 	"github.com/coreos/etcd/third_party/github.com/coreos/go-etcd/etcd"
+	"github.com/coreos/etcd/third_party/github.com/stretchr/testify/assert"
 )

 // Create a five nodes
@ -73,8 +77,8 @@ func TestMultiNodeKillAllAndRecovery(t *testing.T) {
 		t.Fatalf("Recovery error: %s", err)
 	}

-	if result.Node.ModifiedIndex != 16 {
-		t.Fatalf("recovery failed! [%d/16]", result.Node.ModifiedIndex)
+	if result.Node.ModifiedIndex != 17 {
+		t.Fatalf("recovery failed! [%d/17]", result.Node.ModifiedIndex)
 	}
 }

@ -148,7 +152,90 @@ func TestTLSMultiNodeKillAllAndRecovery(t *testing.T) {
 		t.Fatalf("Recovery error: %s", err)
 	}

-	if result.Node.ModifiedIndex != 16 {
-		t.Fatalf("recovery failed! [%d/16]", result.Node.ModifiedIndex)
+	if result.Node.ModifiedIndex != 17 {
+		t.Fatalf("recovery failed! [%d/17]", result.Node.ModifiedIndex)
 	}
 }
+
+// Create a five-node cluster
+// Kill all the nodes and restart
+func TestMultiNodeKillAllAndRecoveryWithStandbys(t *testing.T) {
+	procAttr := new(os.ProcAttr)
+	procAttr.Files = []*os.File{nil, os.Stdout, os.Stderr}
+
+	stop := make(chan bool)
+	leaderChan := make(chan string, 1)
+	all := make(chan bool, 1)
+
+	clusterSize := 5
+	argGroup, etcds, err := CreateCluster(clusterSize, procAttr, false)
+	defer DestroyCluster(etcds)
+
+	if err != nil {
+		t.Fatal("cannot create cluster")
+	}
+
+	c := etcd.NewClient(nil)
+
+	go Monitor(clusterSize, clusterSize, leaderChan, all, stop)
+	<-all
+	<-leaderChan
+	stop <- true
+
+	c.SyncCluster()
+
+	// Reconfigure with smaller active size (3 nodes) and wait for demotion.
+	resp, _ := tests.Put("http://localhost:7001/v2/admin/config", "application/json", bytes.NewBufferString(`{"activeSize":3}`))
+	if !assert.Equal(t, resp.StatusCode, 200) {
+		t.FailNow()
+	}
+
+	time.Sleep(2*server.ActiveMonitorTimeout + (1 * time.Second))
+
+	// Verify that there is three machines in peer mode.
+	result, err := c.Get("_etcd/machines", false, true)
+	assert.NoError(t, err)
+	assert.Equal(t, len(result.Node.Nodes), 3)
+
+	// send 10 commands
+	for i := 0; i < 10; i++ {
+		// Test Set
+		_, err := c.Set("foo", "bar", 0)
+		if err != nil {
+			panic(err)
+		}
+	}
+
+	time.Sleep(time.Second)
+
+	// kill all
+	DestroyCluster(etcds)
+
+	time.Sleep(time.Second)
+
+	stop = make(chan bool)
+	leaderChan = make(chan string, 1)
+	all = make(chan bool, 1)
+
+	time.Sleep(time.Second)
+
+	for i := 0; i < clusterSize; i++ {
+		etcds[i], err = os.StartProcess(EtcdBinPath, argGroup[i], procAttr)
+	}
+
+	time.Sleep(2 * time.Second)
+
+	// send 10 commands
+	for i := 0; i < 10; i++ {
+		// Test Set
+		_, err := c.Set("foo", "bar", 0)
+		if err != nil {
+			t.Fatalf("Recovery error: %s", err)
+		}
+	}
+
+	// Verify that we have three machines.
+	result, err = c.Get("_etcd/machines", false, true)
+	assert.NoError(t, err)
+	assert.Equal(t, len(result.Node.Nodes), 3)
+}
--- a/tests/functional/remove_node_test.go
+++ b/tests/functional/remove_node_test.go
@ -1,6 +1,7 @@
 package test

 import (
+	"bytes"
 	"fmt"
 	"net/http"
 	"os"
@ -8,6 +9,9 @@ import (
 	"time"

 	"github.com/coreos/etcd/third_party/github.com/coreos/go-etcd/etcd"
+
+	"github.com/coreos/etcd/tests"
+	"github.com/coreos/etcd/third_party/github.com/stretchr/testify/assert"
 )

 // remove the node and node rejoin with previous log
@ -25,6 +29,11 @@ func TestRemoveNode(t *testing.T) {

 	c.SyncCluster()

+	resp, _ := tests.Put("http://localhost:7001/v2/admin/config", "application/json", bytes.NewBufferString(`{"syncClusterInterval":1}`))
+	if !assert.Equal(t, resp.StatusCode, 200) {
+		t.FailNow()
+	}
+
 	rmReq, _ := http.NewRequest("DELETE", "http://127.0.0.1:7001/remove/node3", nil)

 	client := &http.Client{}
@ -33,7 +42,7 @@ func TestRemoveNode(t *testing.T) {
 			client.Do(rmReq)

 			fmt.Println("send remove to node3 and wait for its exiting")
-			etcds[2].Wait()
+			time.Sleep(100 * time.Millisecond)

 			resp, err := c.Get("_etcd/machines", false, false)

@ -45,6 +54,9 @@ func TestRemoveNode(t *testing.T) {
 				t.Fatal("cannot remove peer")
 			}

+			etcds[2].Kill()
+			etcds[2].Wait()
+
 			if i == 1 {
 				// rejoin with log
 				etcds[2], err = os.StartProcess(EtcdBinPath, argGroup[2], procAttr)
@ -57,7 +69,7 @@ func TestRemoveNode(t *testing.T) {
 				panic(err)
 			}

-			time.Sleep(time.Second)
+			time.Sleep(time.Second + time.Second)

 			resp, err = c.Get("_etcd/machines", false, false)

--- a/tests/functional/standby_test.go
+++ b/tests/functional/standby_test.go
@ -13,22 +13,44 @@ import (
 	"github.com/coreos/etcd/third_party/github.com/stretchr/testify/assert"
 )

-// Create a full cluster and then add extra an extra standby node.
+// Create a full cluster and then change the active size.
 func TestStandby(t *testing.T) {
-	t.Skip("functionality unimplemented")
-
-	clusterSize := 10 // DefaultActiveSize + 1
+	clusterSize := 15
 	_, etcds, err := CreateCluster(clusterSize, &os.ProcAttr{Files: []*os.File{nil, os.Stdout, os.Stderr}}, false)
-	assert.NoError(t, err)
-	defer DestroyCluster(etcds)
-
-	if err != nil {
+	if !assert.NoError(t, err) {
 		t.Fatal("cannot create cluster")
 	}
+	defer DestroyCluster(etcds)

+	resp, _ := tests.Put("http://localhost:7001/v2/admin/config", "application/json", bytes.NewBufferString(`{"syncClusterInterval":1}`))
+	if !assert.Equal(t, resp.StatusCode, 200) {
+		t.FailNow()
+	}
+
+	time.Sleep(time.Second)
 	c := etcd.NewClient(nil)
 	c.SyncCluster()

+	// Verify that we just have default machines.
+	result, err := c.Get("_etcd/machines", false, true)
+	assert.NoError(t, err)
+	assert.Equal(t, len(result.Node.Nodes), 9)
+
+	fmt.Println("Reconfigure with a smaller active size")
+	resp, _ = tests.Put("http://localhost:7001/v2/admin/config", "application/json", bytes.NewBufferString(`{"activeSize":7, "syncClusterInterval":1}`))
+	if !assert.Equal(t, resp.StatusCode, 200) {
+		t.FailNow()
+	}
+
+	// Wait for two monitor cycles before checking for demotion.
+	time.Sleep((2 * server.ActiveMonitorTimeout) + (2 * time.Second))
+
+	// Verify that we now have seven peers.
+	result, err = c.Get("_etcd/machines", false, true)
+	assert.NoError(t, err)
+	assert.Equal(t, len(result.Node.Nodes), 7)
+
+	fmt.Println("Test the functionality of all servers")
 	// Set key.
 	time.Sleep(time.Second)
 	if _, err := c.Set("foo", "bar", 0); err != nil {
@ -47,49 +69,23 @@ func TestStandby(t *testing.T) {
 		}
 	}

-	// Verify that we have one standby.
-	result, err := c.Get("_etcd/standbys", false, true)
-	assert.NoError(t, err)
-	assert.Equal(t, len(result.Node.Nodes), 1)
-
-	// Reconfigure with larger active size (10 nodes) and wait for promotion.
-	resp, _ := tests.Put("http://localhost:7001/v2/admin/config", "application/json", bytes.NewBufferString(`{"activeSize":10, "promoteDelay":1800}`))
+	fmt.Println("Reconfigure with larger active size and wait for join")
+	resp, _ = tests.Put("http://localhost:7001/v2/admin/config", "application/json", bytes.NewBufferString(`{"activeSize":8, "syncClusterInterval":1}`))
 	if !assert.Equal(t, resp.StatusCode, 200) {
 		t.FailNow()
 	}

-	time.Sleep(server.ActiveMonitorTimeout + (1 * time.Second))
+	time.Sleep((1 * time.Second) + (1 * time.Second))

-	// Verify that the standby node is now a peer.
-	result, err = c.Get("_etcd/standbys", false, true)
-	assert.NoError(t, err)
-	assert.Equal(t, len(result.Node.Nodes), 0)
-
-	// Reconfigure with a smaller active size (8 nodes).
-	resp, _ = tests.Put("http://localhost:7001/v2/admin/config", "application/json", bytes.NewBufferString(`{"activeSize":8, "promoteDelay":1800}`))
-	if !assert.Equal(t, resp.StatusCode, 200) {
-		t.FailNow()
-	}
-
-	// Wait for two monitor cycles before checking for demotion.
-	time.Sleep((2 * server.ActiveMonitorTimeout) + (1 * time.Second))
-
-	// Verify that we now have eight peers.
+	// Verify that exactly eight machines are in the cluster.
 	result, err = c.Get("_etcd/machines", false, true)
 	assert.NoError(t, err)
 	assert.Equal(t, len(result.Node.Nodes), 8)
-
-	// Verify that we now have two standbys.
-	result, err = c.Get("_etcd/standbys", false, true)
-	assert.NoError(t, err)
-	assert.Equal(t, len(result.Node.Nodes), 2)
 }

-// Create a full cluster, disconnect a peer, wait for autodemotion, wait for autopromotion.
-func TestStandbyAutoPromote(t *testing.T) {
-	t.Skip("functionality unimplemented")
-
-	clusterSize := 10 // DefaultActiveSize + 1
+// Create a full cluster, disconnect a peer, wait for removal, wait for standby join.
+func TestStandbyAutoJoin(t *testing.T) {
+	clusterSize := 5
 	_, etcds, err := CreateCluster(clusterSize, &os.ProcAttr{Files: []*os.File{nil, os.Stdout, os.Stderr}}, false)
 	if err != nil {
 		t.Fatal("cannot create cluster")
@ -105,17 +101,25 @@ func TestStandbyAutoPromote(t *testing.T) {

 	time.Sleep(1 * time.Second)

-	// Verify that we have one standby.
-	result, err := c.Get("_etcd/standbys", false, true)
+	// Verify that we have five machines.
+	result, err := c.Get("_etcd/machines", false, true)
 	assert.NoError(t, err)
-	assert.Equal(t, len(result.Node.Nodes), 1)
+	assert.Equal(t, len(result.Node.Nodes), 5)

 	// Reconfigure with a short promote delay (2 second).
-	resp, _ := tests.Put("http://localhost:7001/v2/admin/config", "application/json", bytes.NewBufferString(`{"activeSize":9, "promoteDelay":2}`))
+	resp, _ := tests.Put("http://localhost:7001/v2/admin/config", "application/json", bytes.NewBufferString(`{"activeSize":4, "removeDelay":2, "syncClusterInterval":1}`))
 	if !assert.Equal(t, resp.StatusCode, 200) {
 		t.FailNow()
 	}

+	// Wait for a monitor cycle before checking for removal.
+	time.Sleep(server.ActiveMonitorTimeout + (1 * time.Second))
+
+	// Verify that we now have four peers.
+	result, err = c.Get("_etcd/machines", false, true)
+	assert.NoError(t, err)
+	assert.Equal(t, len(result.Node.Nodes), 4)
+
 	// Remove peer.
 	etcd := etcds[1]
 	etcds = append(etcds[:1], etcds[2:]...)
@ -125,24 +129,153 @@ func TestStandbyAutoPromote(t *testing.T) {
 	etcd.Release()

 	// Wait for it to get dropped.
-	time.Sleep(server.PeerActivityMonitorTimeout + (2 * time.Second))
+	time.Sleep(server.PeerActivityMonitorTimeout + (1 * time.Second))

-	// Wait for the standby to be promoted.
-	time.Sleep(server.ActiveMonitorTimeout + (2 * time.Second))
+	// Wait for the standby to join.
+	time.Sleep((1 * time.Second) + (1 * time.Second))

-	// Verify that we have 9 peers.
+	// Verify that we have 4 peers.
 	result, err = c.Get("_etcd/machines", true, true)
 	assert.NoError(t, err)
-	assert.Equal(t, len(result.Node.Nodes), 9)
+	assert.Equal(t, len(result.Node.Nodes), 4)

-	// Verify that node10 is one of those peers.
-	result, err = c.Get("_etcd/machines/node10", false, false)
-	assert.NoError(t, err)
+	// Verify that node2 is not one of those peers.
+	_, err = c.Get("_etcd/machines/node2", false, false)
+	assert.Error(t, err)
+}

-	// Verify that there are no more standbys.
-	result, err = c.Get("_etcd/standbys", false, true)
+// Create a full cluster and then change the active size gradually.
+func TestStandbyGradualChange(t *testing.T) {
+	clusterSize := 9
+	_, etcds, err := CreateCluster(clusterSize, &os.ProcAttr{Files: []*os.File{nil, os.Stdout, os.Stderr}}, false)
 	assert.NoError(t, err)
-	if assert.Equal(t, len(result.Node.Nodes), 1) {
-		assert.Equal(t, result.Node.Nodes[0].Key, "/_etcd/standbys/node2")
+	defer DestroyCluster(etcds)
+
+	if err != nil {
+		t.Fatal("cannot create cluster")
+	}
+
+	time.Sleep(time.Second)
+	c := etcd.NewClient(nil)
+	c.SyncCluster()
+
+	num := clusterSize
+	for inc := 0; inc < 2; inc++ {
+		for i := 0; i < 6; i++ {
+			// Verify that we just have i machines.
+			result, err := c.Get("_etcd/machines", false, true)
+			assert.NoError(t, err)
+			assert.Equal(t, len(result.Node.Nodes), num)
+
+			if inc == 0 {
+				num--
+			} else {
+				num++
+			}
+
+			fmt.Println("Reconfigure with active size", num)
+			resp, _ := tests.Put("http://localhost:7001/v2/admin/config", "application/json", bytes.NewBufferString(fmt.Sprintf(`{"activeSize":%d, "syncClusterInterval":1}`, num)))
+			if !assert.Equal(t, resp.StatusCode, 200) {
+				t.FailNow()
+			}
+
+			if inc == 0 {
+				// Wait for monitor cycles before checking for demotion.
+				time.Sleep(server.ActiveMonitorTimeout + (1 * time.Second))
+			} else {
+				time.Sleep(time.Second + (1 * time.Second))
+			}
+
+			// Verify that we now have peers.
+			result, err = c.Get("_etcd/machines", false, true)
+			assert.NoError(t, err)
+			assert.Equal(t, len(result.Node.Nodes), num)
+
+			fmt.Println("Test the functionality of all servers")
+			// Set key.
+			if _, err := c.Set("foo", "bar", 0); err != nil {
+				panic(err)
+			}
+			time.Sleep(100 * time.Millisecond)
+
+			// Check that all peers and standbys have the value.
+			for i := range etcds {
+				resp, err := tests.Get(fmt.Sprintf("http://localhost:%d/v2/keys/foo", 4000+(i+1)))
+				if assert.NoError(t, err) {
+					body := tests.ReadBodyJSON(resp)
+					if node, _ := body["node"].(map[string]interface{}); assert.NotNil(t, node) {
+						assert.Equal(t, node["value"], "bar")
+					}
+				}
+			}
+		}
+	}
+}
+
+// Create a full cluster and then change the active size dramatically.
+func TestStandbyDramaticChange(t *testing.T) {
+	clusterSize := 9
+	_, etcds, err := CreateCluster(clusterSize, &os.ProcAttr{Files: []*os.File{nil, os.Stdout, os.Stderr}}, false)
+	assert.NoError(t, err)
+	defer DestroyCluster(etcds)
+
+	if err != nil {
+		t.Fatal("cannot create cluster")
+	}
+
+	time.Sleep(time.Second)
+	c := etcd.NewClient(nil)
+	c.SyncCluster()
+
+	num := clusterSize
+	for i := 0; i < 3; i++ {
+		for inc := 0; inc < 2; inc++ {
+			// Verify that we just have i machines.
+			result, err := c.Get("_etcd/machines", false, true)
+			assert.NoError(t, err)
+			assert.Equal(t, len(result.Node.Nodes), num)
+
+			if inc == 0 {
+				num -= 6
+			} else {
+				num += 6
+			}
+
+			fmt.Println("Reconfigure with active size", num)
+			resp, _ := tests.Put("http://localhost:7001/v2/admin/config", "application/json", bytes.NewBufferString(fmt.Sprintf(`{"activeSize":%d, "syncClusterInterval":1}`, num)))
+			if !assert.Equal(t, resp.StatusCode, 200) {
+				t.FailNow()
+			}
+
+			if inc == 0 {
+				// Wait for monitor cycles before checking for demotion.
+				time.Sleep(6*server.ActiveMonitorTimeout + (1 * time.Second))
+			} else {
+				time.Sleep(time.Second + (1 * time.Second))
+			}
+
+			// Verify that we now have peers.
+			result, err = c.Get("_etcd/machines", false, true)
+			assert.NoError(t, err)
+			assert.Equal(t, len(result.Node.Nodes), num)
+
+			fmt.Println("Test the functionality of all servers")
+			// Set key.
+			if _, err := c.Set("foo", "bar", 0); err != nil {
+				panic(err)
+			}
+			time.Sleep(100 * time.Millisecond)
+
+			// Check that all peers and standbys have the value.
+			for i := range etcds {
+				resp, err := tests.Get(fmt.Sprintf("http://localhost:%d/v2/keys/foo", 4000+(i+1)))
+				if assert.NoError(t, err) {
+					body := tests.ReadBodyJSON(resp)
+					if node, _ := body["node"].(map[string]interface{}); assert.NotNil(t, node) {
+						assert.Equal(t, node["value"], "bar")
+					}
+				}
+			}
+		}
 	}
 }