diff --git a/vendor/go.etcd.io/etcd/etcdserver/cluster_util.go b/vendor/go.etcd.io/etcd/etcdserver/cluster_util.go
new file mode 100644
index 0000000..f92706c
--- /dev/null
+++ b/vendor/go.etcd.io/etcd/etcdserver/cluster_util.go
@@ -0,0 +1,407 @@
+// 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 etcdserver
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+	"sort"
+	"strings"
+	"time"
+
+	"go.etcd.io/etcd/etcdserver/api/membership"
+	"go.etcd.io/etcd/pkg/types"
+	"go.etcd.io/etcd/version"
+
+	"github.com/coreos/go-semver/semver"
+	"go.uber.org/zap"
+)
+
+// isMemberBootstrapped tries to check if the given member has been bootstrapped
+// in the given cluster.
+func isMemberBootstrapped(lg *zap.Logger, cl *membership.RaftCluster, member string, rt http.RoundTripper, timeout time.Duration) bool {
+	rcl, err := getClusterFromRemotePeers(lg, getRemotePeerURLs(cl, member), timeout, false, rt)
+	if err != nil {
+		return false
+	}
+	id := cl.MemberByName(member).ID
+	m := rcl.Member(id)
+	if m == nil {
+		return false
+	}
+	if len(m.ClientURLs) > 0 {
+		return true
+	}
+	return false
+}
+
+// GetClusterFromRemotePeers takes a set of URLs representing etcd peers, and
+// attempts to construct a Cluster by accessing the members endpoint on one of
+// these URLs. The first URL to provide a response is used. If no URLs provide
+// a response, or a Cluster cannot be successfully created from a received
+// response, an error is returned.
+// Each request has a 10-second timeout. Because the upper limit of TTL is 5s,
+// 10 second is enough for building connection and finishing request.
+func GetClusterFromRemotePeers(lg *zap.Logger, urls []string, rt http.RoundTripper) (*membership.RaftCluster, error) {
+	return getClusterFromRemotePeers(lg, urls, 10*time.Second, true, rt)
+}
+
+// If logerr is true, it prints out more error messages.
+func getClusterFromRemotePeers(lg *zap.Logger, urls []string, timeout time.Duration, logerr bool, rt http.RoundTripper) (*membership.RaftCluster, error) {
+	cc := &http.Client{
+		Transport: rt,
+		Timeout:   timeout,
+	}
+	for _, u := range urls {
+		addr := u + "/members"
+		resp, err := cc.Get(addr)
+		if err != nil {
+			if logerr {
+				if lg != nil {
+					lg.Warn("failed to get cluster response", zap.String("address", addr), zap.Error(err))
+				} else {
+					plog.Warningf("could not get cluster response from %s: %v", u, err)
+				}
+			}
+			continue
+		}
+		b, err := ioutil.ReadAll(resp.Body)
+		resp.Body.Close()
+		if err != nil {
+			if logerr {
+				if lg != nil {
+					lg.Warn("failed to read body of cluster response", zap.String("address", addr), zap.Error(err))
+				} else {
+					plog.Warningf("could not read the body of cluster response: %v", err)
+				}
+			}
+			continue
+		}
+		var membs []*membership.Member
+		if err = json.Unmarshal(b, &membs); err != nil {
+			if logerr {
+				if lg != nil {
+					lg.Warn("failed to unmarshal cluster response", zap.String("address", addr), zap.Error(err))
+				} else {
+					plog.Warningf("could not unmarshal cluster response: %v", err)
+				}
+			}
+			continue
+		}
+		id, err := types.IDFromString(resp.Header.Get("X-Etcd-Cluster-ID"))
+		if err != nil {
+			if logerr {
+				if lg != nil {
+					lg.Warn(
+						"failed to parse cluster ID",
+						zap.String("address", addr),
+						zap.String("header", resp.Header.Get("X-Etcd-Cluster-ID")),
+						zap.Error(err),
+					)
+				} else {
+					plog.Warningf("could not parse the cluster ID from cluster res: %v", err)
+				}
+			}
+			continue
+		}
+
+		// check the length of membership members
+		// if the membership members are present then prepare and return raft cluster
+		// if membership members are not present then the raft cluster formed will be
+		// an invalid empty cluster hence return failed to get raft cluster member(s) from the given urls error
+		if len(membs) > 0 {
+			return membership.NewClusterFromMembers(lg, "", id, membs), nil
+		}
+		return nil, fmt.Errorf("failed to get raft cluster member(s) from the given URLs")
+	}
+	return nil, fmt.Errorf("could not retrieve cluster information from the given URLs")
+}
+
+// getRemotePeerURLs returns peer urls of remote members in the cluster. The
+// returned list is sorted in ascending lexicographical order.
+func getRemotePeerURLs(cl *membership.RaftCluster, local string) []string {
+	us := make([]string, 0)
+	for _, m := range cl.Members() {
+		if m.Name == local {
+			continue
+		}
+		us = append(us, m.PeerURLs...)
+	}
+	sort.Strings(us)
+	return us
+}
+
+// getVersions returns the versions of the members in the given cluster.
+// The key of the returned map is the member's ID. The value of the returned map
+// is the semver versions string, including server and cluster.
+// If it fails to get the version of a member, the key will be nil.
+func getVersions(lg *zap.Logger, cl *membership.RaftCluster, local types.ID, rt http.RoundTripper) map[string]*version.Versions {
+	members := cl.Members()
+	vers := make(map[string]*version.Versions)
+	for _, m := range members {
+		if m.ID == local {
+			cv := "not_decided"
+			if cl.Version() != nil {
+				cv = cl.Version().String()
+			}
+			vers[m.ID.String()] = &version.Versions{Server: version.Version, Cluster: cv}
+			continue
+		}
+		ver, err := getVersion(lg, m, rt)
+		if err != nil {
+			if lg != nil {
+				lg.Warn("failed to get version", zap.String("remote-member-id", m.ID.String()), zap.Error(err))
+			} else {
+				plog.Warningf("cannot get the version of member %s (%v)", m.ID, err)
+			}
+			vers[m.ID.String()] = nil
+		} else {
+			vers[m.ID.String()] = ver
+		}
+	}
+	return vers
+}
+
+// decideClusterVersion decides the cluster version based on the versions map.
+// The returned version is the min server version in the map, or nil if the min
+// version in unknown.
+func decideClusterVersion(lg *zap.Logger, vers map[string]*version.Versions) *semver.Version {
+	var cv *semver.Version
+	lv := semver.Must(semver.NewVersion(version.Version))
+
+	for mid, ver := range vers {
+		if ver == nil {
+			return nil
+		}
+		v, err := semver.NewVersion(ver.Server)
+		if err != nil {
+			if lg != nil {
+				lg.Warn(
+					"failed to parse server version of remote member",
+					zap.String("remote-member-id", mid),
+					zap.String("remote-member-version", ver.Server),
+					zap.Error(err),
+				)
+			} else {
+				plog.Errorf("cannot understand the version of member %s (%v)", mid, err)
+			}
+			return nil
+		}
+		if lv.LessThan(*v) {
+			if lg != nil {
+				lg.Warn(
+					"leader found higher-versioned member",
+					zap.String("local-member-version", lv.String()),
+					zap.String("remote-member-id", mid),
+					zap.String("remote-member-version", ver.Server),
+				)
+			} else {
+				plog.Warningf("the local etcd version %s is not up-to-date", lv.String())
+				plog.Warningf("member %s has a higher version %s", mid, ver.Server)
+			}
+		}
+		if cv == nil {
+			cv = v
+		} else if v.LessThan(*cv) {
+			cv = v
+		}
+	}
+	return cv
+}
+
+// isCompatibleWithCluster return true if the local member has a compatible version with
+// the current running cluster.
+// The version is considered as compatible when at least one of the other members in the cluster has a
+// cluster version in the range of [MinClusterVersion, Version] and no known members has a cluster version
+// out of the range.
+// We set this rule since when the local member joins, another member might be offline.
+func isCompatibleWithCluster(lg *zap.Logger, cl *membership.RaftCluster, local types.ID, rt http.RoundTripper) bool {
+	vers := getVersions(lg, cl, local, rt)
+	minV := semver.Must(semver.NewVersion(version.MinClusterVersion))
+	maxV := semver.Must(semver.NewVersion(version.Version))
+	maxV = &semver.Version{
+		Major: maxV.Major,
+		Minor: maxV.Minor,
+	}
+	return isCompatibleWithVers(lg, vers, local, minV, maxV)
+}
+
+func isCompatibleWithVers(lg *zap.Logger, vers map[string]*version.Versions, local types.ID, minV, maxV *semver.Version) bool {
+	var ok bool
+	for id, v := range vers {
+		// ignore comparison with local version
+		if id == local.String() {
+			continue
+		}
+		if v == nil {
+			continue
+		}
+		clusterv, err := semver.NewVersion(v.Cluster)
+		if err != nil {
+			if lg != nil {
+				lg.Warn(
+					"failed to parse cluster version of remote member",
+					zap.String("remote-member-id", id),
+					zap.String("remote-member-cluster-version", v.Cluster),
+					zap.Error(err),
+				)
+			} else {
+				plog.Errorf("cannot understand the cluster version of member %s (%v)", id, err)
+			}
+			continue
+		}
+		if clusterv.LessThan(*minV) {
+			if lg != nil {
+				lg.Warn(
+					"cluster version of remote member is not compatible; too low",
+					zap.String("remote-member-id", id),
+					zap.String("remote-member-cluster-version", clusterv.String()),
+					zap.String("minimum-cluster-version-supported", minV.String()),
+				)
+			} else {
+				plog.Warningf("the running cluster version(%v) is lower than the minimal cluster version(%v) supported", clusterv.String(), minV.String())
+			}
+			return false
+		}
+		if maxV.LessThan(*clusterv) {
+			if lg != nil {
+				lg.Warn(
+					"cluster version of remote member is not compatible; too high",
+					zap.String("remote-member-id", id),
+					zap.String("remote-member-cluster-version", clusterv.String()),
+					zap.String("minimum-cluster-version-supported", minV.String()),
+				)
+			} else {
+				plog.Warningf("the running cluster version(%v) is higher than the maximum cluster version(%v) supported", clusterv.String(), maxV.String())
+			}
+			return false
+		}
+		ok = true
+	}
+	return ok
+}
+
+// getVersion returns the Versions of the given member via its
+// peerURLs. Returns the last error if it fails to get the version.
+func getVersion(lg *zap.Logger, m *membership.Member, rt http.RoundTripper) (*version.Versions, error) {
+	cc := &http.Client{
+		Transport: rt,
+	}
+	var (
+		err  error
+		resp *http.Response
+	)
+
+	for _, u := range m.PeerURLs {
+		addr := u + "/version"
+		resp, err = cc.Get(addr)
+		if err != nil {
+			if lg != nil {
+				lg.Warn(
+					"failed to reach the peer URL",
+					zap.String("address", addr),
+					zap.String("remote-member-id", m.ID.String()),
+					zap.Error(err),
+				)
+			} else {
+				plog.Warningf("failed to reach the peerURL(%s) of member %s (%v)", u, m.ID, err)
+			}
+			continue
+		}
+		var b []byte
+		b, err = ioutil.ReadAll(resp.Body)
+		resp.Body.Close()
+		if err != nil {
+			if lg != nil {
+				lg.Warn(
+					"failed to read body of response",
+					zap.String("address", addr),
+					zap.String("remote-member-id", m.ID.String()),
+					zap.Error(err),
+				)
+			} else {
+				plog.Warningf("failed to read out the response body from the peerURL(%s) of member %s (%v)", u, m.ID, err)
+			}
+			continue
+		}
+		var vers version.Versions
+		if err = json.Unmarshal(b, &vers); err != nil {
+			if lg != nil {
+				lg.Warn(
+					"failed to unmarshal response",
+					zap.String("address", addr),
+					zap.String("remote-member-id", m.ID.String()),
+					zap.Error(err),
+				)
+			} else {
+				plog.Warningf("failed to unmarshal the response body got from the peerURL(%s) of member %s (%v)", u, m.ID, err)
+			}
+			continue
+		}
+		return &vers, nil
+	}
+	return nil, err
+}
+
+func promoteMemberHTTP(ctx context.Context, url string, id uint64, peerRt http.RoundTripper) ([]*membership.Member, error) {
+	cc := &http.Client{Transport: peerRt}
+	// TODO: refactor member http handler code
+	// cannot import etcdhttp, so manually construct url
+	requestUrl := url + "/members/promote/" + fmt.Sprintf("%d", id)
+	req, err := http.NewRequest("POST", requestUrl, nil)
+	if err != nil {
+		return nil, err
+	}
+	req = req.WithContext(ctx)
+	resp, err := cc.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+	b, err := ioutil.ReadAll(resp.Body)
+	if err != nil {
+		return nil, err
+	}
+
+	if resp.StatusCode == http.StatusRequestTimeout {
+		return nil, ErrTimeout
+	}
+	if resp.StatusCode == http.StatusPreconditionFailed {
+		// both ErrMemberNotLearner and ErrLearnerNotReady have same http status code
+		if strings.Contains(string(b), ErrLearnerNotReady.Error()) {
+			return nil, ErrLearnerNotReady
+		}
+		if strings.Contains(string(b), membership.ErrMemberNotLearner.Error()) {
+			return nil, membership.ErrMemberNotLearner
+		}
+		return nil, fmt.Errorf("member promote: unknown error(%s)", string(b))
+	}
+	if resp.StatusCode == http.StatusNotFound {
+		return nil, membership.ErrIDNotFound
+	}
+
+	if resp.StatusCode != http.StatusOK { // all other types of errors
+		return nil, fmt.Errorf("member promote: unknown error(%s)", string(b))
+	}
+
+	var membs []*membership.Member
+	if err := json.Unmarshal(b, &membs); err != nil {
+		return nil, err
+	}
+	return membs, nil
+}