diff --git a/vendor/github.com/coreos/etcd/etcdserver/membership/cluster.go b/vendor/github.com/coreos/etcd/etcdserver/membership/cluster.go
new file mode 100644
index 0000000..ba5c541
--- /dev/null
+++ b/vendor/github.com/coreos/etcd/etcdserver/membership/cluster.go
@@ -0,0 +1,518 @@
+// Copyright 2015 The etcd Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package membership
+
+import (
+	"bytes"
+	"context"
+	"crypto/sha1"
+	"encoding/binary"
+	"encoding/json"
+	"fmt"
+	"path"
+	"sort"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/coreos/etcd/mvcc/backend"
+	"github.com/coreos/etcd/pkg/netutil"
+	"github.com/coreos/etcd/pkg/types"
+	"github.com/coreos/etcd/raft"
+	"github.com/coreos/etcd/raft/raftpb"
+	"github.com/coreos/etcd/store"
+	"github.com/coreos/etcd/version"
+
+	"github.com/coreos/go-semver/semver"
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+// RaftCluster is a list of Members that belong to the same raft cluster
+type RaftCluster struct {
+	id    types.ID
+	token string
+
+	store store.Store
+	be    backend.Backend
+
+	sync.Mutex // guards the fields below
+	version    *semver.Version
+	members    map[types.ID]*Member
+	// removed contains the ids of removed members in the cluster.
+	// removed id cannot be reused.
+	removed map[types.ID]bool
+}
+
+func NewClusterFromURLsMap(token string, urlsmap types.URLsMap) (*RaftCluster, error) {
+	c := NewCluster(token)
+	for name, urls := range urlsmap {
+		m := NewMember(name, urls, token, nil)
+		if _, ok := c.members[m.ID]; ok {
+			return nil, fmt.Errorf("member exists with identical ID %v", m)
+		}
+		if uint64(m.ID) == raft.None {
+			return nil, fmt.Errorf("cannot use %x as member id", raft.None)
+		}
+		c.members[m.ID] = m
+	}
+	c.genID()
+	return c, nil
+}
+
+func NewClusterFromMembers(token string, id types.ID, membs []*Member) *RaftCluster {
+	c := NewCluster(token)
+	c.id = id
+	for _, m := range membs {
+		c.members[m.ID] = m
+	}
+	return c
+}
+
+func NewCluster(token string) *RaftCluster {
+	return &RaftCluster{
+		token:   token,
+		members: make(map[types.ID]*Member),
+		removed: make(map[types.ID]bool),
+	}
+}
+
+func (c *RaftCluster) ID() types.ID { return c.id }
+
+func (c *RaftCluster) Members() []*Member {
+	c.Lock()
+	defer c.Unlock()
+	var ms MembersByID
+	for _, m := range c.members {
+		ms = append(ms, m.Clone())
+	}
+	sort.Sort(ms)
+	return []*Member(ms)
+}
+
+func (c *RaftCluster) Member(id types.ID) *Member {
+	c.Lock()
+	defer c.Unlock()
+	return c.members[id].Clone()
+}
+
+// MemberByName returns a Member with the given name if exists.
+// If more than one member has the given name, it will panic.
+func (c *RaftCluster) MemberByName(name string) *Member {
+	c.Lock()
+	defer c.Unlock()
+	var memb *Member
+	for _, m := range c.members {
+		if m.Name == name {
+			if memb != nil {
+				plog.Panicf("two members with the given name %q exist", name)
+			}
+			memb = m
+		}
+	}
+	return memb.Clone()
+}
+
+func (c *RaftCluster) MemberIDs() []types.ID {
+	c.Lock()
+	defer c.Unlock()
+	var ids []types.ID
+	for _, m := range c.members {
+		ids = append(ids, m.ID)
+	}
+	sort.Sort(types.IDSlice(ids))
+	return ids
+}
+
+func (c *RaftCluster) IsIDRemoved(id types.ID) bool {
+	c.Lock()
+	defer c.Unlock()
+	return c.removed[id]
+}
+
+// PeerURLs returns a list of all peer addresses.
+// The returned list is sorted in ascending lexicographical order.
+func (c *RaftCluster) PeerURLs() []string {
+	c.Lock()
+	defer c.Unlock()
+	urls := make([]string, 0)
+	for _, p := range c.members {
+		urls = append(urls, p.PeerURLs...)
+	}
+	sort.Strings(urls)
+	return urls
+}
+
+// ClientURLs returns a list of all client addresses.
+// The returned list is sorted in ascending lexicographical order.
+func (c *RaftCluster) ClientURLs() []string {
+	c.Lock()
+	defer c.Unlock()
+	urls := make([]string, 0)
+	for _, p := range c.members {
+		urls = append(urls, p.ClientURLs...)
+	}
+	sort.Strings(urls)
+	return urls
+}
+
+func (c *RaftCluster) String() string {
+	c.Lock()
+	defer c.Unlock()
+	b := &bytes.Buffer{}
+	fmt.Fprintf(b, "{ClusterID:%s ", c.id)
+	var ms []string
+	for _, m := range c.members {
+		ms = append(ms, fmt.Sprintf("%+v", m))
+	}
+	fmt.Fprintf(b, "Members:[%s] ", strings.Join(ms, " "))
+	var ids []string
+	for id := range c.removed {
+		ids = append(ids, id.String())
+	}
+	fmt.Fprintf(b, "RemovedMemberIDs:[%s]}", strings.Join(ids, " "))
+	return b.String()
+}
+
+func (c *RaftCluster) genID() {
+	mIDs := c.MemberIDs()
+	b := make([]byte, 8*len(mIDs))
+	for i, id := range mIDs {
+		binary.BigEndian.PutUint64(b[8*i:], uint64(id))
+	}
+	hash := sha1.Sum(b)
+	c.id = types.ID(binary.BigEndian.Uint64(hash[:8]))
+}
+
+func (c *RaftCluster) SetID(id types.ID) { c.id = id }
+
+func (c *RaftCluster) SetStore(st store.Store) { c.store = st }
+
+func (c *RaftCluster) SetBackend(be backend.Backend) {
+	c.be = be
+	mustCreateBackendBuckets(c.be)
+}
+
+func (c *RaftCluster) Recover(onSet func(*semver.Version)) {
+	c.Lock()
+	defer c.Unlock()
+
+	c.members, c.removed = membersFromStore(c.store)
+	c.version = clusterVersionFromStore(c.store)
+	mustDetectDowngrade(c.version)
+	onSet(c.version)
+
+	for _, m := range c.members {
+		plog.Infof("added member %s %v to cluster %s from store", m.ID, m.PeerURLs, c.id)
+	}
+	if c.version != nil {
+		plog.Infof("set the cluster version to %v from store", version.Cluster(c.version.String()))
+	}
+}
+
+// ValidateConfigurationChange takes a proposed ConfChange and
+// ensures that it is still valid.
+func (c *RaftCluster) ValidateConfigurationChange(cc raftpb.ConfChange) error {
+	members, removed := membersFromStore(c.store)
+	id := types.ID(cc.NodeID)
+	if removed[id] {
+		return ErrIDRemoved
+	}
+	switch cc.Type {
+	case raftpb.ConfChangeAddNode:
+		if members[id] != nil {
+			return ErrIDExists
+		}
+		urls := make(map[string]bool)
+		for _, m := range members {
+			for _, u := range m.PeerURLs {
+				urls[u] = true
+			}
+		}
+		m := new(Member)
+		if err := json.Unmarshal(cc.Context, m); err != nil {
+			plog.Panicf("unmarshal member should never fail: %v", err)
+		}
+		for _, u := range m.PeerURLs {
+			if urls[u] {
+				return ErrPeerURLexists
+			}
+		}
+	case raftpb.ConfChangeRemoveNode:
+		if members[id] == nil {
+			return ErrIDNotFound
+		}
+	case raftpb.ConfChangeUpdateNode:
+		if members[id] == nil {
+			return ErrIDNotFound
+		}
+		urls := make(map[string]bool)
+		for _, m := range members {
+			if m.ID == id {
+				continue
+			}
+			for _, u := range m.PeerURLs {
+				urls[u] = true
+			}
+		}
+		m := new(Member)
+		if err := json.Unmarshal(cc.Context, m); err != nil {
+			plog.Panicf("unmarshal member should never fail: %v", err)
+		}
+		for _, u := range m.PeerURLs {
+			if urls[u] {
+				return ErrPeerURLexists
+			}
+		}
+	default:
+		plog.Panicf("ConfChange type should be either AddNode, RemoveNode or UpdateNode")
+	}
+	return nil
+}
+
+// AddMember adds a new Member into the cluster, and saves the given member's
+// raftAttributes into the store. The given member should have empty attributes.
+// A Member with a matching id must not exist.
+func (c *RaftCluster) AddMember(m *Member) {
+	c.Lock()
+	defer c.Unlock()
+	if c.store != nil {
+		mustSaveMemberToStore(c.store, m)
+	}
+	if c.be != nil {
+		mustSaveMemberToBackend(c.be, m)
+	}
+
+	c.members[m.ID] = m
+
+	plog.Infof("added member %s %v to cluster %s", m.ID, m.PeerURLs, c.id)
+}
+
+// RemoveMember removes a member from the store.
+// The given id MUST exist, or the function panics.
+func (c *RaftCluster) RemoveMember(id types.ID) {
+	c.Lock()
+	defer c.Unlock()
+	if c.store != nil {
+		mustDeleteMemberFromStore(c.store, id)
+	}
+	if c.be != nil {
+		mustDeleteMemberFromBackend(c.be, id)
+	}
+
+	delete(c.members, id)
+	c.removed[id] = true
+
+	plog.Infof("removed member %s from cluster %s", id, c.id)
+}
+
+func (c *RaftCluster) UpdateAttributes(id types.ID, attr Attributes) {
+	c.Lock()
+	defer c.Unlock()
+	if m, ok := c.members[id]; ok {
+		m.Attributes = attr
+		if c.store != nil {
+			mustUpdateMemberAttrInStore(c.store, m)
+		}
+		if c.be != nil {
+			mustSaveMemberToBackend(c.be, m)
+		}
+		return
+	}
+	_, ok := c.removed[id]
+	if !ok {
+		plog.Panicf("error updating attributes of unknown member %s", id)
+	}
+	plog.Warningf("skipped updating attributes of removed member %s", id)
+}
+
+func (c *RaftCluster) UpdateRaftAttributes(id types.ID, raftAttr RaftAttributes) {
+	c.Lock()
+	defer c.Unlock()
+
+	c.members[id].RaftAttributes = raftAttr
+	if c.store != nil {
+		mustUpdateMemberInStore(c.store, c.members[id])
+	}
+	if c.be != nil {
+		mustSaveMemberToBackend(c.be, c.members[id])
+	}
+
+	plog.Noticef("updated member %s %v in cluster %s", id, raftAttr.PeerURLs, c.id)
+}
+
+func (c *RaftCluster) Version() *semver.Version {
+	c.Lock()
+	defer c.Unlock()
+	if c.version == nil {
+		return nil
+	}
+	return semver.Must(semver.NewVersion(c.version.String()))
+}
+
+func (c *RaftCluster) SetVersion(ver *semver.Version, onSet func(*semver.Version)) {
+	c.Lock()
+	defer c.Unlock()
+	if c.version != nil {
+		plog.Noticef("updated the cluster version from %v to %v", version.Cluster(c.version.String()), version.Cluster(ver.String()))
+	} else {
+		plog.Noticef("set the initial cluster version to %v", version.Cluster(ver.String()))
+	}
+	oldVer := c.version
+	c.version = ver
+	mustDetectDowngrade(c.version)
+	if c.store != nil {
+		mustSaveClusterVersionToStore(c.store, ver)
+	}
+	if c.be != nil {
+		mustSaveClusterVersionToBackend(c.be, ver)
+	}
+	if oldVer != nil {
+		ClusterVersionMetrics.With(prometheus.Labels{"cluster_version": version.Cluster(oldVer.String())}).Set(0)
+	}
+	ClusterVersionMetrics.With(prometheus.Labels{"cluster_version": version.Cluster(ver.String())}).Set(1)
+	onSet(ver)
+}
+
+func (c *RaftCluster) IsReadyToAddNewMember() bool {
+	nmembers := 1
+	nstarted := 0
+
+	for _, member := range c.members {
+		if member.IsStarted() {
+			nstarted++
+		}
+		nmembers++
+	}
+
+	if nstarted == 1 && nmembers == 2 {
+		// a case of adding a new node to 1-member cluster for restoring cluster data
+		// https://github.com/coreos/etcd/blob/master/Documentation/v2/admin_guide.md#restoring-the-cluster
+
+		plog.Debugf("The number of started member is 1. This cluster can accept add member request.")
+		return true
+	}
+
+	nquorum := nmembers/2 + 1
+	if nstarted < nquorum {
+		plog.Warningf("Reject add member request: the number of started member (%d) will be less than the quorum number of the cluster (%d)", nstarted, nquorum)
+		return false
+	}
+
+	return true
+}
+
+func (c *RaftCluster) IsReadyToRemoveMember(id uint64) bool {
+	nmembers := 0
+	nstarted := 0
+
+	for _, member := range c.members {
+		if uint64(member.ID) == id {
+			continue
+		}
+
+		if member.IsStarted() {
+			nstarted++
+		}
+		nmembers++
+	}
+
+	nquorum := nmembers/2 + 1
+	if nstarted < nquorum {
+		plog.Warningf("Reject remove member request: the number of started member (%d) will be less than the quorum number of the cluster (%d)", nstarted, nquorum)
+		return false
+	}
+
+	return true
+}
+
+func membersFromStore(st store.Store) (map[types.ID]*Member, map[types.ID]bool) {
+	members := make(map[types.ID]*Member)
+	removed := make(map[types.ID]bool)
+	e, err := st.Get(StoreMembersPrefix, true, true)
+	if err != nil {
+		if isKeyNotFound(err) {
+			return members, removed
+		}
+		plog.Panicf("get storeMembers should never fail: %v", err)
+	}
+	for _, n := range e.Node.Nodes {
+		var m *Member
+		m, err = nodeToMember(n)
+		if err != nil {
+			plog.Panicf("nodeToMember should never fail: %v", err)
+		}
+		members[m.ID] = m
+	}
+
+	e, err = st.Get(storeRemovedMembersPrefix, true, true)
+	if err != nil {
+		if isKeyNotFound(err) {
+			return members, removed
+		}
+		plog.Panicf("get storeRemovedMembers should never fail: %v", err)
+	}
+	for _, n := range e.Node.Nodes {
+		removed[MustParseMemberIDFromKey(n.Key)] = true
+	}
+	return members, removed
+}
+
+func clusterVersionFromStore(st store.Store) *semver.Version {
+	e, err := st.Get(path.Join(storePrefix, "version"), false, false)
+	if err != nil {
+		if isKeyNotFound(err) {
+			return nil
+		}
+		plog.Panicf("unexpected error (%v) when getting cluster version from store", err)
+	}
+	return semver.Must(semver.NewVersion(*e.Node.Value))
+}
+
+// ValidateClusterAndAssignIDs validates the local cluster by matching the PeerURLs
+// with the existing cluster. If the validation succeeds, it assigns the IDs
+// from the existing cluster to the local cluster.
+// If the validation fails, an error will be returned.
+func ValidateClusterAndAssignIDs(local *RaftCluster, existing *RaftCluster) error {
+	ems := existing.Members()
+	lms := local.Members()
+	if len(ems) != len(lms) {
+		return fmt.Errorf("member count is unequal")
+	}
+	sort.Sort(MembersByPeerURLs(ems))
+	sort.Sort(MembersByPeerURLs(lms))
+
+	ctx, cancel := context.WithTimeout(context.TODO(), 30*time.Second)
+	defer cancel()
+	for i := range ems {
+		if ok, err := netutil.URLStringsEqual(ctx, ems[i].PeerURLs, lms[i].PeerURLs); !ok {
+			return fmt.Errorf("unmatched member while checking PeerURLs (%v)", err)
+		}
+		lms[i].ID = ems[i].ID
+	}
+	local.members = make(map[types.ID]*Member)
+	for _, m := range lms {
+		local.members[m.ID] = m
+	}
+	return nil
+}
+
+func mustDetectDowngrade(cv *semver.Version) {
+	lv := semver.Must(semver.NewVersion(version.Version))
+	// only keep major.minor version for comparison against cluster version
+	lv = &semver.Version{Major: lv.Major, Minor: lv.Minor}
+	if cv != nil && lv.LessThan(*cv) {
+		plog.Fatalf("cluster cannot be downgraded (current version: %s is lower than determined cluster version: %s).", version.Version, version.Cluster(cv.String()))
+	}
+}