diff --git a/vendor/go.etcd.io/etcd/etcdserver/api/membership/cluster.go b/vendor/go.etcd.io/etcd/etcdserver/api/membership/cluster.go
new file mode 100644
index 0000000..89a6edd
--- /dev/null
+++ b/vendor/go.etcd.io/etcd/etcdserver/api/membership/cluster.go
@@ -0,0 +1,841 @@
+// 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"
+
+	"go.etcd.io/etcd/etcdserver/api/v2store"
+	"go.etcd.io/etcd/mvcc/backend"
+	"go.etcd.io/etcd/pkg/netutil"
+	"go.etcd.io/etcd/pkg/types"
+	"go.etcd.io/etcd/raft"
+	"go.etcd.io/etcd/raft/raftpb"
+	"go.etcd.io/etcd/version"
+
+	"github.com/coreos/go-semver/semver"
+	"github.com/prometheus/client_golang/prometheus"
+	"go.uber.org/zap"
+)
+
+const maxLearners = 1
+
+// RaftCluster is a list of Members that belong to the same raft cluster
+type RaftCluster struct {
+	lg *zap.Logger
+
+	localID types.ID
+	cid     types.ID
+	token   string
+
+	v2store v2store.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
+}
+
+// ConfigChangeContext represents a context for confChange.
+type ConfigChangeContext struct {
+	Member
+	// IsPromote indicates if the config change is for promoting a learner member.
+	// This flag is needed because both adding a new member and promoting a learner member
+	// uses the same config change type 'ConfChangeAddNode'.
+	IsPromote bool `json:"isPromote"`
+}
+
+// NewClusterFromURLsMap creates a new raft cluster using provided urls map. Currently, it does not support creating
+// cluster with raft learner member.
+func NewClusterFromURLsMap(lg *zap.Logger, token string, urlsmap types.URLsMap) (*RaftCluster, error) {
+	c := NewCluster(lg, 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(lg *zap.Logger, token string, id types.ID, membs []*Member) *RaftCluster {
+	c := NewCluster(lg, token)
+	c.cid = id
+	for _, m := range membs {
+		c.members[m.ID] = m
+	}
+	return c
+}
+
+func NewCluster(lg *zap.Logger, token string) *RaftCluster {
+	return &RaftCluster{
+		lg:      lg,
+		token:   token,
+		members: make(map[types.ID]*Member),
+		removed: make(map[types.ID]bool),
+	}
+}
+
+func (c *RaftCluster) ID() types.ID { return c.cid }
+
+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()
+}
+
+func (c *RaftCluster) VotingMembers() []*Member {
+	c.Lock()
+	defer c.Unlock()
+	var ms MembersByID
+	for _, m := range c.members {
+		if !m.IsLearner {
+			ms = append(ms, m.Clone())
+		}
+	}
+	sort.Sort(ms)
+	return []*Member(ms)
+}
+
+// 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 {
+				if c.lg != nil {
+					c.lg.Panic("two member with same name found", zap.String("name", name))
+				} else {
+					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.cid)
+	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.cid = types.ID(binary.BigEndian.Uint64(hash[:8]))
+}
+
+func (c *RaftCluster) SetID(localID, cid types.ID) {
+	c.localID = localID
+	c.cid = cid
+}
+
+func (c *RaftCluster) SetStore(st v2store.Store) { c.v2store = st }
+
+func (c *RaftCluster) SetBackend(be backend.Backend) {
+	c.be = be
+	mustCreateBackendBuckets(c.be)
+}
+
+func (c *RaftCluster) Recover(onSet func(*zap.Logger, *semver.Version)) {
+	c.Lock()
+	defer c.Unlock()
+
+	c.members, c.removed = membersFromStore(c.lg, c.v2store)
+	c.version = clusterVersionFromStore(c.lg, c.v2store)
+	mustDetectDowngrade(c.lg, c.version)
+	onSet(c.lg, c.version)
+
+	for _, m := range c.members {
+		if c.lg != nil {
+			c.lg.Info(
+				"recovered/added member from store",
+				zap.String("cluster-id", c.cid.String()),
+				zap.String("local-member-id", c.localID.String()),
+				zap.String("recovered-remote-peer-id", m.ID.String()),
+				zap.Strings("recovered-remote-peer-urls", m.PeerURLs),
+			)
+		} else {
+			plog.Infof("added member %s %v to cluster %s from store", m.ID, m.PeerURLs, c.cid)
+		}
+	}
+	if c.version != nil {
+		if c.lg != nil {
+			c.lg.Info(
+				"set cluster version from store",
+				zap.String("cluster-version", version.Cluster(c.version.String())),
+			)
+		} else {
+			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.lg, c.v2store)
+	id := types.ID(cc.NodeID)
+	if removed[id] {
+		return ErrIDRemoved
+	}
+	switch cc.Type {
+	case raftpb.ConfChangeAddNode, raftpb.ConfChangeAddLearnerNode:
+		confChangeContext := new(ConfigChangeContext)
+		if err := json.Unmarshal(cc.Context, confChangeContext); err != nil {
+			if c.lg != nil {
+				c.lg.Panic("failed to unmarshal confChangeContext", zap.Error(err))
+			} else {
+				plog.Panicf("unmarshal confChangeContext should never fail: %v", err)
+			}
+		}
+
+		if confChangeContext.IsPromote { // promoting a learner member to voting member
+			if members[id] == nil {
+				return ErrIDNotFound
+			}
+			if !members[id].IsLearner {
+				return ErrMemberNotLearner
+			}
+		} else { // adding a new member
+			if members[id] != nil {
+				return ErrIDExists
+			}
+
+			urls := make(map[string]bool)
+			for _, m := range members {
+				for _, u := range m.PeerURLs {
+					urls[u] = true
+				}
+			}
+			for _, u := range confChangeContext.Member.PeerURLs {
+				if urls[u] {
+					return ErrPeerURLexists
+				}
+			}
+
+			if confChangeContext.Member.IsLearner { // the new member is a learner
+				numLearners := 0
+				for _, m := range members {
+					if m.IsLearner {
+						numLearners++
+					}
+				}
+				if numLearners+1 > maxLearners {
+					return ErrTooManyLearners
+				}
+			}
+		}
+	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 {
+			if c.lg != nil {
+				c.lg.Panic("failed to unmarshal member", zap.Error(err))
+			} else {
+				plog.Panicf("unmarshal member should never fail: %v", err)
+			}
+		}
+		for _, u := range m.PeerURLs {
+			if urls[u] {
+				return ErrPeerURLexists
+			}
+		}
+
+	default:
+		if c.lg != nil {
+			c.lg.Panic("unknown ConfChange type", zap.String("type", cc.Type.String()))
+		} else {
+			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.v2store != nil {
+		mustSaveMemberToStore(c.v2store, m)
+	}
+	if c.be != nil {
+		mustSaveMemberToBackend(c.be, m)
+	}
+
+	c.members[m.ID] = m
+
+	if c.lg != nil {
+		c.lg.Info(
+			"added member",
+			zap.String("cluster-id", c.cid.String()),
+			zap.String("local-member-id", c.localID.String()),
+			zap.String("added-peer-id", m.ID.String()),
+			zap.Strings("added-peer-peer-urls", m.PeerURLs),
+		)
+	} else {
+		plog.Infof("added member %s %v to cluster %s", m.ID, m.PeerURLs, c.cid)
+	}
+}
+
+// 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.v2store != nil {
+		mustDeleteMemberFromStore(c.v2store, id)
+	}
+	if c.be != nil {
+		mustDeleteMemberFromBackend(c.be, id)
+	}
+
+	m, ok := c.members[id]
+	delete(c.members, id)
+	c.removed[id] = true
+
+	if c.lg != nil {
+		if ok {
+			c.lg.Info(
+				"removed member",
+				zap.String("cluster-id", c.cid.String()),
+				zap.String("local-member-id", c.localID.String()),
+				zap.String("removed-remote-peer-id", id.String()),
+				zap.Strings("removed-remote-peer-urls", m.PeerURLs),
+			)
+		} else {
+			c.lg.Warn(
+				"skipped removing already removed member",
+				zap.String("cluster-id", c.cid.String()),
+				zap.String("local-member-id", c.localID.String()),
+				zap.String("removed-remote-peer-id", id.String()),
+			)
+		}
+	} else {
+		plog.Infof("removed member %s from cluster %s", id, c.cid)
+	}
+}
+
+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.v2store != nil {
+			mustUpdateMemberAttrInStore(c.v2store, m)
+		}
+		if c.be != nil {
+			mustSaveMemberToBackend(c.be, m)
+		}
+		return
+	}
+
+	_, ok := c.removed[id]
+	if !ok {
+		if c.lg != nil {
+			c.lg.Panic(
+				"failed to update; member unknown",
+				zap.String("cluster-id", c.cid.String()),
+				zap.String("local-member-id", c.localID.String()),
+				zap.String("unknown-remote-peer-id", id.String()),
+			)
+		} else {
+			plog.Panicf("error updating attributes of unknown member %s", id)
+		}
+	}
+
+	if c.lg != nil {
+		c.lg.Warn(
+			"skipped attributes update of removed member",
+			zap.String("cluster-id", c.cid.String()),
+			zap.String("local-member-id", c.localID.String()),
+			zap.String("updated-peer-id", id.String()),
+		)
+	} else {
+		plog.Warningf("skipped updating attributes of removed member %s", id)
+	}
+}
+
+// PromoteMember marks the member's IsLearner RaftAttributes to false.
+func (c *RaftCluster) PromoteMember(id types.ID) {
+	c.Lock()
+	defer c.Unlock()
+
+	c.members[id].RaftAttributes.IsLearner = false
+	if c.v2store != nil {
+		mustUpdateMemberInStore(c.v2store, c.members[id])
+	}
+	if c.be != nil {
+		mustSaveMemberToBackend(c.be, c.members[id])
+	}
+
+	if c.lg != nil {
+		c.lg.Info(
+			"promote member",
+			zap.String("cluster-id", c.cid.String()),
+			zap.String("local-member-id", c.localID.String()),
+		)
+	} else {
+		plog.Noticef("promote member %s in cluster %s", id, c.cid)
+	}
+}
+
+func (c *RaftCluster) UpdateRaftAttributes(id types.ID, raftAttr RaftAttributes) {
+	c.Lock()
+	defer c.Unlock()
+
+	c.members[id].RaftAttributes = raftAttr
+	if c.v2store != nil {
+		mustUpdateMemberInStore(c.v2store, c.members[id])
+	}
+	if c.be != nil {
+		mustSaveMemberToBackend(c.be, c.members[id])
+	}
+
+	if c.lg != nil {
+		c.lg.Info(
+			"updated member",
+			zap.String("cluster-id", c.cid.String()),
+			zap.String("local-member-id", c.localID.String()),
+			zap.String("updated-remote-peer-id", id.String()),
+			zap.Strings("updated-remote-peer-urls", raftAttr.PeerURLs),
+		)
+	} else {
+		plog.Noticef("updated member %s %v in cluster %s", id, raftAttr.PeerURLs, c.cid)
+	}
+}
+
+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(*zap.Logger, *semver.Version)) {
+	c.Lock()
+	defer c.Unlock()
+	if c.version != nil {
+		if c.lg != nil {
+			c.lg.Info(
+				"updated cluster version",
+				zap.String("cluster-id", c.cid.String()),
+				zap.String("local-member-id", c.localID.String()),
+				zap.String("from", version.Cluster(c.version.String())),
+				zap.String("from", version.Cluster(ver.String())),
+			)
+		} else {
+			plog.Noticef("updated the cluster version from %v to %v", version.Cluster(c.version.String()), version.Cluster(ver.String()))
+		}
+	} else {
+		if c.lg != nil {
+			c.lg.Info(
+				"set initial cluster version",
+				zap.String("cluster-id", c.cid.String()),
+				zap.String("local-member-id", c.localID.String()),
+				zap.String("cluster-version", version.Cluster(ver.String())),
+			)
+		} else {
+			plog.Noticef("set the initial cluster version to %v", version.Cluster(ver.String()))
+		}
+	}
+	c.version = ver
+	mustDetectDowngrade(c.lg, c.version)
+	if c.v2store != nil {
+		mustSaveClusterVersionToStore(c.v2store, ver)
+	}
+	if c.be != nil {
+		mustSaveClusterVersionToBackend(c.be, ver)
+	}
+	ClusterVersionMetrics.With(prometheus.Labels{"cluster_version": ver.String()}).Set(1)
+	onSet(c.lg, ver)
+}
+
+func (c *RaftCluster) IsReadyToAddVotingMember() bool {
+	nmembers := 1
+	nstarted := 0
+
+	for _, member := range c.VotingMembers() {
+		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/etcd-io/etcd/blob/master/Documentation/v2/admin_guide.md#restoring-the-cluster
+		if c.lg != nil {
+			c.lg.Debug("number of started member is 1; can accept add member request")
+		} else {
+			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 {
+		if c.lg != nil {
+			c.lg.Warn(
+				"rejecting member add; started member will be less than quorum",
+				zap.Int("number-of-started-member", nstarted),
+				zap.Int("quorum", nquorum),
+				zap.String("cluster-id", c.cid.String()),
+				zap.String("local-member-id", c.localID.String()),
+			)
+		} else {
+			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) IsReadyToRemoveVotingMember(id uint64) bool {
+	nmembers := 0
+	nstarted := 0
+
+	for _, member := range c.VotingMembers() {
+		if uint64(member.ID) == id {
+			continue
+		}
+
+		if member.IsStarted() {
+			nstarted++
+		}
+		nmembers++
+	}
+
+	nquorum := nmembers/2 + 1
+	if nstarted < nquorum {
+		if c.lg != nil {
+			c.lg.Warn(
+				"rejecting member remove; started member will be less than quorum",
+				zap.Int("number-of-started-member", nstarted),
+				zap.Int("quorum", nquorum),
+				zap.String("cluster-id", c.cid.String()),
+				zap.String("local-member-id", c.localID.String()),
+			)
+		} else {
+			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 (c *RaftCluster) IsReadyToPromoteMember(id uint64) bool {
+	nmembers := 1
+	nstarted := 0
+
+	for _, member := range c.VotingMembers() {
+		if member.IsStarted() {
+			nstarted++
+		}
+		nmembers++
+	}
+
+	nquorum := nmembers/2 + 1
+	if nstarted < nquorum {
+		if c.lg != nil {
+			c.lg.Warn(
+				"rejecting member promote; started member will be less than quorum",
+				zap.Int("number-of-started-member", nstarted),
+				zap.Int("quorum", nquorum),
+				zap.String("cluster-id", c.cid.String()),
+				zap.String("local-member-id", c.localID.String()),
+			)
+		} else {
+			plog.Warningf("Reject promote 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(lg *zap.Logger, st v2store.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
+		}
+		if lg != nil {
+			lg.Panic("failed to get members from store", zap.String("path", StoreMembersPrefix), zap.Error(err))
+		} else {
+			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 {
+			if lg != nil {
+				lg.Panic("failed to nodeToMember", zap.Error(err))
+			} else {
+				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
+		}
+		if lg != nil {
+			lg.Panic(
+				"failed to get removed members from store",
+				zap.String("path", storeRemovedMembersPrefix),
+				zap.Error(err),
+			)
+		} else {
+			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(lg *zap.Logger, st v2store.Store) *semver.Version {
+	e, err := st.Get(path.Join(storePrefix, "version"), false, false)
+	if err != nil {
+		if isKeyNotFound(err) {
+			return nil
+		}
+		if lg != nil {
+			lg.Panic(
+				"failed to get cluster version from store",
+				zap.String("path", path.Join(storePrefix, "version")),
+				zap.Error(err),
+			)
+		} else {
+			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(lg *zap.Logger, local *RaftCluster, existing *RaftCluster) error {
+	ems := existing.Members()
+	lms := local.Members()
+	if len(ems) != len(lms) {
+		return fmt.Errorf("member count is unequal")
+	}
+
+	ctx, cancel := context.WithTimeout(context.TODO(), 30*time.Second)
+	defer cancel()
+	for i := range ems {
+		var err error
+		ok := false
+		for j := range lms {
+			if ok, err = netutil.URLStringsEqual(ctx, lg, ems[i].PeerURLs, lms[j].PeerURLs); ok {
+				lms[j].ID = ems[i].ID
+				break
+			}
+		}
+		if !ok {
+			return fmt.Errorf("PeerURLs: no match found for existing member (%v, %v), last resolver error (%v)", ems[i].ID, ems[i].PeerURLs, err)
+		}
+	}
+	local.members = make(map[types.ID]*Member)
+	for _, m := range lms {
+		local.members[m.ID] = m
+	}
+	return nil
+}
+
+func mustDetectDowngrade(lg *zap.Logger, 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) {
+		if lg != nil {
+			lg.Fatal(
+				"invalid downgrade; server version is lower than determined cluster version",
+				zap.String("current-server-version", version.Version),
+				zap.String("determined-cluster-version", version.Cluster(cv.String())),
+			)
+		} else {
+			plog.Fatalf("cluster cannot be downgraded (current version: %s is lower than determined cluster version: %s).", version.Version, version.Cluster(cv.String()))
+		}
+	}
+}
+
+// IsLocalMemberLearner returns if the local member is raft learner
+func (c *RaftCluster) IsLocalMemberLearner() bool {
+	c.Lock()
+	defer c.Unlock()
+	localMember, ok := c.members[c.localID]
+	if !ok {
+		if c.lg != nil {
+			c.lg.Panic(
+				"failed to find local ID in cluster members",
+				zap.String("cluster-id", c.cid.String()),
+				zap.String("local-member-id", c.localID.String()),
+			)
+		} else {
+			plog.Panicf("failed to find local ID %s in cluster %s", c.localID.String(), c.cid.String())
+		}
+	}
+	return localMember.IsLearner
+}
+
+// IsMemberExist returns if the member with the given id exists in cluster.
+func (c *RaftCluster) IsMemberExist(id types.ID) bool {
+	c.Lock()
+	defer c.Unlock()
+	_, ok := c.members[id]
+	return ok
+}
+
+// VotingMemberIDs returns the ID of voting members in cluster.
+func (c *RaftCluster) VotingMemberIDs() []types.ID {
+	c.Lock()
+	defer c.Unlock()
+	var ids []types.ID
+	for _, m := range c.members {
+		if !m.IsLearner {
+			ids = append(ids, m.ID)
+		}
+	}
+	sort.Sort(types.IDSlice(ids))
+	return ids
+}