etcd.go

// Copyright 2016 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 embed

import (
	"context"
	"errors"
	"fmt"
	"io"
	defaultLog "log"
	"math"
	"net"
	"net/http"
	"net/url"
	"runtime"
	"sort"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/soheilhy/cmux"
	"go.uber.org/zap"
	"google.golang.org/grpc"
	"google.golang.org/grpc/credentials/insecure"
	"google.golang.org/grpc/keepalive"

	"go.etcd.io/etcd/api/v3/version"
	"go.etcd.io/etcd/client/pkg/v3/transport"
	"go.etcd.io/etcd/client/pkg/v3/types"
	"go.etcd.io/etcd/client/v3/credentials"
	"go.etcd.io/etcd/pkg/v3/debugutil"
	runtimeutil "go.etcd.io/etcd/pkg/v3/runtime"
	"go.etcd.io/etcd/server/v3/config"
	"go.etcd.io/etcd/server/v3/etcdserver"
	"go.etcd.io/etcd/server/v3/etcdserver/api/etcdhttp"
	"go.etcd.io/etcd/server/v3/etcdserver/api/rafthttp"
	"go.etcd.io/etcd/server/v3/features"
	"go.etcd.io/etcd/server/v3/storage"
	"go.etcd.io/etcd/server/v3/verify"
)

const (
	// internal fd usage includes disk usage and transport usage.
	// To read/write snapshot, snap pkg needs 1. In normal case, wal pkg needs
	// at most 2 to read/lock/write WALs. One case that it needs to 2 is to
	// read all logs after some snapshot index, which locates at the end of
	// the second last and the head of the last. For purging, it needs to read
	// directory, so it needs 1. For fd monitor, it needs 1.
	// For transport, rafthttp builds two long-polling connections and at most
	// four temporary connections with each member. There are at most 9 members
	// in a cluster, so it should reserve 96.
	// For the safety, we set the total reserved number to 150.
	reservedInternalFDNum = 150
)

// Etcd contains a running etcd server and its listeners.
type Etcd struct {
	Peers   []*peerListener
	Clients []net.Listener
	// a map of contexts for the servers that serves client requests.
	sctxs            map[string]*serveCtx
	metricsListeners []net.Listener

	tracingExporterShutdown func()

	Server *etcdserver.EtcdServer

	cfg Config

	// closeOnce is to ensure `stopc` is closed only once, no matter
	// how many times the Close() method is called.
	closeOnce sync.Once
	// stopc is used to notify the sub goroutines not to send
	// any errors to `errc`.
	stopc chan struct{}
	// errc is used to receive error from sub goroutines (including
	// client handler, peer handler and metrics handler). It's closed
	// after all these sub goroutines exit (checked via `wg`). Writers
	// should avoid writing after `stopc` is closed by selecting on
	// reading from `stopc`.
	errc chan error

	// wg is used to track the lifecycle of all sub goroutines which
	// need to send error back to the `errc`.
	wg sync.WaitGroup
}

type peerListener struct {
	net.Listener
	serve func() error
	close func(context.Context) error
}

// StartEtcd launches the etcd server and HTTP handlers for client/server communication.
// The returned Etcd.Server is not guaranteed to have joined the cluster. Wait
// on the Etcd.Server.ReadyNotify() channel to know when it completes and is ready for use.
func StartEtcd(inCfg *Config) (e *Etcd, err error) {
	if err = inCfg.Validate(); err != nil {
		return nil, err
	}
	serving := false
	e = &Etcd{cfg: *inCfg, stopc: make(chan struct{})}
	cfg := &e.cfg
	defer func() {
		if e == nil || err == nil {
			return
		}
		if !serving {
			// errored before starting gRPC server for serveCtx.serversC
			for _, sctx := range e.sctxs {
				sctx.close()
			}
		}
		e.Close()
		e = nil
	}()

	if !cfg.SocketOpts.Empty() {
		cfg.logger.Info(
			"configuring socket options",
			zap.Bool("reuse-address", cfg.SocketOpts.ReuseAddress),
			zap.Bool("reuse-port", cfg.SocketOpts.ReusePort),
		)
	}
	e.cfg.logger.Info(
		"configuring peer listeners",
		zap.Strings("listen-peer-urls", e.cfg.getListenPeerURLs()),
	)
	if e.Peers, err = configurePeerListeners(cfg); err != nil {
		return e, err
	}

	e.cfg.logger.Info(
		"configuring client listeners",
		zap.Strings("listen-client-urls", e.cfg.getListenClientURLs()),
	)
	if e.sctxs, err = configureClientListeners(cfg); err != nil {
		return e, err
	}

	for _, sctx := range e.sctxs {
		e.Clients = append(e.Clients, sctx.l)
	}

	var (
		urlsmap types.URLsMap
		token   string
	)
	memberInitialized := true
	if !isMemberInitialized(cfg) {
		memberInitialized = false
		urlsmap, token, err = cfg.PeerURLsMapAndToken("etcd")
		if err != nil {
			return e, fmt.Errorf("error setting up initial cluster: %w", err)
		}
	}

	// AutoCompactionRetention defaults to "0" if not set.
	if len(cfg.AutoCompactionRetention) == 0 {
		cfg.AutoCompactionRetention = "0"
	}
	autoCompactionRetention, err := parseCompactionRetention(cfg.AutoCompactionMode, cfg.AutoCompactionRetention)
	if err != nil {
		return e, err
	}

	backendFreelistType := parseBackendFreelistType(cfg.BackendFreelistType)

	srvcfg := config.ServerConfig{
		Name:                                 cfg.Name,
		ClientURLs:                           cfg.AdvertiseClientUrls,
		PeerURLs:                             cfg.AdvertisePeerUrls,
		DataDir:                              cfg.Dir,
		DedicatedWALDir:                      cfg.WalDir,
		SnapshotCount:                        cfg.SnapshotCount,
		SnapshotCatchUpEntries:               cfg.SnapshotCatchUpEntries,
		MaxSnapFiles:                         cfg.MaxSnapFiles,
		MaxWALFiles:                          cfg.MaxWalFiles,
		InitialPeerURLsMap:                   urlsmap,
		InitialClusterToken:                  token,
		DiscoveryURL:                         cfg.Durl,
		DiscoveryProxy:                       cfg.Dproxy,
		DiscoveryCfg:                         cfg.DiscoveryCfg,
		NewCluster:                           cfg.IsNewCluster(),
		PeerTLSInfo:                          cfg.PeerTLSInfo,
		TickMs:                               cfg.TickMs,
		ElectionTicks:                        cfg.ElectionTicks(),
		InitialElectionTickAdvance:           cfg.InitialElectionTickAdvance,
		AutoCompactionRetention:              autoCompactionRetention,
		AutoCompactionMode:                   cfg.AutoCompactionMode,
		QuotaBackendBytes:                    cfg.QuotaBackendBytes,
		BackendBatchLimit:                    cfg.BackendBatchLimit,
		BackendFreelistType:                  backendFreelistType,
		BackendBatchInterval:                 cfg.BackendBatchInterval,
		MaxTxnOps:                            cfg.MaxTxnOps,
		MaxRequestBytes:                      cfg.MaxRequestBytes,
		MaxConcurrentStreams:                 cfg.MaxConcurrentStreams,
		SocketOpts:                           cfg.SocketOpts,
		StrictReconfigCheck:                  cfg.StrictReconfigCheck,
		ClientCertAuthEnabled:                cfg.ClientTLSInfo.ClientCertAuth,
		AuthToken:                            cfg.AuthToken,
		BcryptCost:                           cfg.BcryptCost,
		TokenTTL:                             cfg.AuthTokenTTL,
		CORS:                                 cfg.CORS,
		HostWhitelist:                        cfg.HostWhitelist,
		CorruptCheckTime:                     cfg.CorruptCheckTime,
		CompactHashCheckTime:                 cfg.CompactHashCheckTime,
		PreVote:                              cfg.PreVote,
		Logger:                               cfg.logger,
		ForceNewCluster:                      cfg.ForceNewCluster,
		EnableGRPCGateway:                    cfg.EnableGRPCGateway,
		ExperimentalEnableDistributedTracing: cfg.ExperimentalEnableDistributedTracing,
		UnsafeNoFsync:                        cfg.UnsafeNoFsync,
		EnableLeaseCheckpoint:                cfg.ExperimentalEnableLeaseCheckpoint,
		LeaseCheckpointPersist:               cfg.ExperimentalEnableLeaseCheckpointPersist,
		CompactionBatchLimit:                 cfg.CompactionBatchLimit,
		CompactionSleepInterval:              cfg.ExperimentalCompactionSleepInterval,
		WatchProgressNotifyInterval:          cfg.WatchProgressNotifyInterval,
		DowngradeCheckTime:                   cfg.ExperimentalDowngradeCheckTime,
		WarningApplyDuration:                 cfg.WarningApplyDuration,
		WarningUnaryRequestDuration:          cfg.WarningUnaryRequestDuration,
		MemoryMlock:                          cfg.MemoryMlock,
		BootstrapDefragThresholdMegabytes:    cfg.BootstrapDefragThresholdMegabytes,
		MaxLearners:                          cfg.MaxLearners,
		V2Deprecation:                        cfg.V2DeprecationEffective(),
		ExperimentalLocalAddress:             cfg.InferLocalAddr(),
		ServerFeatureGate:                    cfg.ServerFeatureGate,
		Metrics:                              cfg.Metrics,
	}

	if srvcfg.ExperimentalEnableDistributedTracing {
		tctx := context.Background()
		tracingExporter, terr := newTracingExporter(tctx, cfg)
		if terr != nil {
			return e, terr
		}
		e.tracingExporterShutdown = func() {
			tracingExporter.Close(tctx)
		}
		srvcfg.ExperimentalTracerOptions = tracingExporter.opts

		e.cfg.logger.Info(
			"distributed tracing setup enabled",
		)
	}

	srvcfg.PeerTLSInfo.LocalAddr = srvcfg.ExperimentalLocalAddress

	print(e.cfg.logger, *cfg, srvcfg, memberInitialized)

	if e.Server, err = etcdserver.NewServer(srvcfg); err != nil {
		return e, err
	}

	// buffer channel so goroutines on closed connections won't wait forever
	e.errc = make(chan error, len(e.Peers)+len(e.Clients)+2*len(e.sctxs))

	// newly started member ("memberInitialized==false")
	// does not need corruption check
	if memberInitialized && srvcfg.ServerFeatureGate.Enabled(features.InitialCorruptCheck) {
		if err = e.Server.CorruptionChecker().InitialCheck(); err != nil {
			// set "EtcdServer" to nil, so that it does not block on "EtcdServer.Close()"
			// (nothing to close since rafthttp transports have not been started)

			e.cfg.logger.Error("checkInitialHashKV failed", zap.Error(err))
			e.Server.Cleanup()
			e.Server = nil
			return e, err
		}
	}
	e.Server.Start()

	e.servePeers()

	e.serveClients()

	if err = e.serveMetrics(); err != nil {
		return e, err
	}

	e.cfg.logger.Info(
		"now serving peer/client/metrics",
		zap.String("local-member-id", e.Server.MemberID().String()),
		zap.Strings("initial-advertise-peer-urls", e.cfg.getAdvertisePeerURLs()),
		zap.Strings("listen-peer-urls", e.cfg.getListenPeerURLs()),
		zap.Strings("advertise-client-urls", e.cfg.getAdvertiseClientURLs()),
		zap.Strings("listen-client-urls", e.cfg.getListenClientURLs()),
		zap.Strings("listen-metrics-urls", e.cfg.getMetricsURLs()),
	)
	serving = true
	return e, nil
}

func print(lg *zap.Logger, ec Config, sc config.ServerConfig, memberInitialized bool) {
	cors := make([]string, 0, len(ec.CORS))
	for v := range ec.CORS {
		cors = append(cors, v)
	}
	sort.Strings(cors)

	hss := make([]string, 0, len(ec.HostWhitelist))
	for v := range ec.HostWhitelist {
		hss = append(hss, v)
	}
	sort.Strings(hss)

	quota := ec.QuotaBackendBytes
	if quota == 0 {
		quota = storage.DefaultQuotaBytes
	}

	lg.Info(
		"starting an etcd server",
		zap.String("etcd-version", version.Version),
		zap.String("git-sha", version.GitSHA),
		zap.String("go-version", runtime.Version()),
		zap.String("go-os", runtime.GOOS),
		zap.String("go-arch", runtime.GOARCH),
		zap.Int("max-cpu-set", runtime.GOMAXPROCS(0)),
		zap.Int("max-cpu-available", runtime.NumCPU()),
		zap.Bool("member-initialized", memberInitialized),
		zap.String("name", sc.Name),
		zap.String("data-dir", sc.DataDir),
		zap.String("wal-dir", ec.WalDir),
		zap.String("wal-dir-dedicated", sc.DedicatedWALDir),
		zap.String("member-dir", sc.MemberDir()),
		zap.Bool("force-new-cluster", sc.ForceNewCluster),
		zap.String("heartbeat-interval", fmt.Sprintf("%v", time.Duration(sc.TickMs)*time.Millisecond)),
		zap.String("election-timeout", fmt.Sprintf("%v", time.Duration(sc.ElectionTicks*int(sc.TickMs))*time.Millisecond)),
		zap.Bool("initial-election-tick-advance", sc.InitialElectionTickAdvance),
		zap.Uint64("snapshot-count", sc.SnapshotCount),
		zap.Uint("max-wals", sc.MaxWALFiles),
		zap.Uint("max-snapshots", sc.MaxSnapFiles),
		zap.Uint64("snapshot-catchup-entries", sc.SnapshotCatchUpEntries),
		zap.Strings("initial-advertise-peer-urls", ec.getAdvertisePeerURLs()),
		zap.Strings("listen-peer-urls", ec.getListenPeerURLs()),
		zap.Strings("advertise-client-urls", ec.getAdvertiseClientURLs()),
		zap.Strings("listen-client-urls", ec.getListenClientURLs()),
		zap.Strings("listen-metrics-urls", ec.getMetricsURLs()),
		zap.Bool("experimental-set-member-localaddr", ec.ExperimentalSetMemberLocalAddr),
		zap.String("experimental-local-address", sc.ExperimentalLocalAddress),
		zap.Strings("cors", cors),
		zap.Strings("host-whitelist", hss),
		zap.String("initial-cluster", sc.InitialPeerURLsMap.String()),
		zap.String("initial-cluster-state", ec.ClusterState),
		zap.String("initial-cluster-token", sc.InitialClusterToken),
		zap.Int64("quota-backend-bytes", quota),
		zap.Uint("max-request-bytes", sc.MaxRequestBytes),
		zap.Uint32("max-concurrent-streams", sc.MaxConcurrentStreams),

		zap.Bool("pre-vote", sc.PreVote),
		zap.String(ServerFeatureGateFlagName, sc.ServerFeatureGate.String()),
		zap.Bool("initial-corrupt-check", sc.InitialCorruptCheck),
		zap.String("corrupt-check-time-interval", sc.CorruptCheckTime.String()),
		zap.Duration("compact-check-time-interval", sc.CompactHashCheckTime),
		zap.String("auto-compaction-mode", sc.AutoCompactionMode),
		zap.Duration("auto-compaction-retention", sc.AutoCompactionRetention),
		zap.String("auto-compaction-interval", sc.AutoCompactionRetention.String()),
		zap.String("discovery-url", sc.DiscoveryURL),
		zap.String("discovery-proxy", sc.DiscoveryProxy),

		zap.String("discovery-token", sc.DiscoveryCfg.Token),
		zap.String("discovery-endpoints", strings.Join(sc.DiscoveryCfg.Endpoints, ",")),
		zap.String("discovery-dial-timeout", sc.DiscoveryCfg.DialTimeout.String()),
		zap.String("discovery-request-timeout", sc.DiscoveryCfg.RequestTimeout.String()),
		zap.String("discovery-keepalive-time", sc.DiscoveryCfg.KeepAliveTime.String()),
		zap.String("discovery-keepalive-timeout", sc.DiscoveryCfg.KeepAliveTimeout.String()),
		zap.Bool("discovery-insecure-transport", sc.DiscoveryCfg.Secure.InsecureTransport),
		zap.Bool("discovery-insecure-skip-tls-verify", sc.DiscoveryCfg.Secure.InsecureSkipVerify),
		zap.String("discovery-cert", sc.DiscoveryCfg.Secure.Cert),
		zap.String("discovery-key", sc.DiscoveryCfg.Secure.Key),
		zap.String("discovery-cacert", sc.DiscoveryCfg.Secure.Cacert),
		zap.String("discovery-user", sc.DiscoveryCfg.Auth.Username),

		zap.String("downgrade-check-interval", sc.DowngradeCheckTime.String()),
		zap.Int("max-learners", sc.MaxLearners),

		zap.String("v2-deprecation", string(ec.V2Deprecation)),
	)
}

// Config returns the current configuration.
func (e *Etcd) Config() Config {
	return e.cfg
}

// Close gracefully shuts down all servers/listeners.
// Client requests will be terminated with request timeout.
// After timeout, enforce remaning requests be closed immediately.
//
// The rough workflow to shut down etcd:
//  1. close the `stopc` channel, so that all error handlers (child
//     goroutines) won't send back any errors anymore;
//  2. stop the http and grpc servers gracefully, within request timeout;
//  3. close all client and metrics listeners, so that etcd server
//     stops receiving any new connection;
//  4. call the cancel function to close the gateway context, so that
//     all gateway connections are closed.
//  5. stop etcd server gracefully, and ensure the main raft loop
//     goroutine is stopped;
//  6. stop all peer listeners, so that it stops receiving peer connections
//     and messages (wait up to 1-second);
//  7. wait for all child goroutines (i.e. client handlers, peer handlers
//     and metrics handlers) to exit;
//  8. close the `errc` channel to release the resource. Note that it's only
//     safe to close the `errc` after step 7 above is done, otherwise the
//     child goroutines may send errors back to already closed `errc` channel.
func (e *Etcd) Close() {
	fields := []zap.Field{
		zap.String("name", e.cfg.Name),
		zap.String("data-dir", e.cfg.Dir),
		zap.Strings("advertise-peer-urls", e.cfg.getAdvertisePeerURLs()),
		zap.Strings("advertise-client-urls", e.cfg.getAdvertiseClientURLs()),
	}
	lg := e.GetLogger()
	lg.Info("closing etcd server", fields...)
	defer func() {
		lg.Info("closed etcd server", fields...)
		verify.MustVerifyIfEnabled(verify.Config{
			Logger:     lg,
			DataDir:    e.cfg.Dir,
			ExactIndex: false,
		})
		lg.Sync()
	}()

	e.closeOnce.Do(func() {
		close(e.stopc)
	})

	// close client requests with request timeout
	timeout := 2 * time.Second
	if e.Server != nil {
		timeout = e.Server.Cfg.ReqTimeout()
	}
	for _, sctx := range e.sctxs {
		for ss := range sctx.serversC {
			ctx, cancel := context.WithTimeout(context.Background(), timeout)
			stopServers(ctx, ss)
			cancel()
		}
	}

	for _, sctx := range e.sctxs {
		sctx.cancel()
	}

	for i := range e.Clients {
		if e.Clients[i] != nil {
			e.Clients[i].Close()
		}
	}

	for i := range e.metricsListeners {
		e.metricsListeners[i].Close()
	}

	// shutdown tracing exporter
	if e.tracingExporterShutdown != nil {
		e.tracingExporterShutdown()
	}

	// close rafthttp transports
	if e.Server != nil {
		e.Server.Stop()
	}

	// close all idle connections in peer handler (wait up to 1-second)
	for i := range e.Peers {
		if e.Peers[i] != nil && e.Peers[i].close != nil {
			ctx, cancel := context.WithTimeout(context.Background(), time.Second)
			e.Peers[i].close(ctx)
			cancel()
		}
	}
	if e.errc != nil {
		e.wg.Wait()
		close(e.errc)
	}
}

func stopServers(ctx context.Context, ss *servers) {
	// first, close the http.Server
	if ss.http != nil {
		ss.http.Shutdown(ctx)
	}
	if ss.grpc == nil {
		return
	}
	// do not grpc.Server.GracefulStop when grpc runs under http server
	// See https://github.com/grpc/grpc-go/issues/1384#issuecomment-317124531
	// and https://github.com/etcd-io/etcd/issues/8916
	if ss.secure && ss.http != nil {
		ss.grpc.Stop()
		return
	}

	ch := make(chan struct{})
	go func() {
		defer close(ch)
		// close listeners to stop accepting new connections,
		// will block on any existing transports
		ss.grpc.GracefulStop()
	}()

	// wait until all pending RPCs are finished
	select {
	case <-ch:
	case <-ctx.Done():
		// took too long, manually close open transports
		// e.g. watch streams
		ss.grpc.Stop()

		// concurrent GracefulStop should be interrupted
		<-ch
	}
}

// Err - return channel used to report errors during etcd run/shutdown.
// Since etcd 3.5 the channel is being closed when the etcd is over.
func (e *Etcd) Err() <-chan error {
	return e.errc
}

func configurePeerListeners(cfg *Config) (peers []*peerListener, err error) {
	if err = updateCipherSuites(&cfg.PeerTLSInfo, cfg.CipherSuites); err != nil {
		return nil, err
	}
	if err = cfg.PeerSelfCert(); err != nil {
		cfg.logger.Fatal("failed to get peer self-signed certs", zap.Error(err))
	}
	updateMinMaxVersions(&cfg.PeerTLSInfo, cfg.TlsMinVersion, cfg.TlsMaxVersion)
	if !cfg.PeerTLSInfo.Empty() {
		cfg.logger.Info(
			"starting with peer TLS",
			zap.String("tls-info", fmt.Sprintf("%+v", cfg.PeerTLSInfo)),
			zap.Strings("cipher-suites", cfg.CipherSuites),
		)
	}

	peers = make([]*peerListener, len(cfg.ListenPeerUrls))
	defer func() {
		if err == nil {
			return
		}
		for i := range peers {
			if peers[i] != nil && peers[i].close != nil {
				cfg.logger.Warn(
					"closing peer listener",
					zap.String("address", cfg.ListenPeerUrls[i].String()),
					zap.Error(err),
				)
				ctx, cancel := context.WithTimeout(context.Background(), time.Second)
				peers[i].close(ctx)
				cancel()
			}
		}
	}()

	for i, u := range cfg.ListenPeerUrls {
		if u.Scheme == "http" {
			if !cfg.PeerTLSInfo.Empty() {
				cfg.logger.Warn("scheme is HTTP while key and cert files are present; ignoring key and cert files", zap.String("peer-url", u.String()))
			}
			if cfg.PeerTLSInfo.ClientCertAuth {
				cfg.logger.Warn("scheme is HTTP while --peer-client-cert-auth is enabled; ignoring client cert auth for this URL", zap.String("peer-url", u.String()))
			}
		}
		peers[i] = &peerListener{close: func(context.Context) error { return nil }}
		peers[i].Listener, err = transport.NewListenerWithOpts(u.Host, u.Scheme,
			transport.WithTLSInfo(&cfg.PeerTLSInfo),
			transport.WithSocketOpts(&cfg.SocketOpts),
			transport.WithTimeout(rafthttp.ConnReadTimeout, rafthttp.ConnWriteTimeout),
		)
		if err != nil {
			cfg.logger.Error("creating peer listener failed", zap.Error(err))
			return nil, err
		}
		// once serve, overwrite with 'http.Server.Shutdown'
		peers[i].close = func(context.Context) error {
			return peers[i].Listener.Close()
		}
	}
	return peers, nil
}

// configure peer handlers after rafthttp.Transport started
func (e *Etcd) servePeers() {
	ph := etcdhttp.NewPeerHandler(e.GetLogger(), e.Server)

	for _, p := range e.Peers {
		u := p.Listener.Addr().String()
		m := cmux.New(p.Listener)
		srv := &http.Server{
			Handler:     ph,
			ReadTimeout: 5 * time.Minute,
			ErrorLog:    defaultLog.New(io.Discard, "", 0), // do not log user error
		}
		go srv.Serve(m.Match(cmux.Any()))
		p.serve = func() error {
			e.cfg.logger.Info(
				"cmux::serve",
				zap.String("address", u),
			)
			return m.Serve()
		}
		p.close = func(ctx context.Context) error {
			// gracefully shutdown http.Server
			// close open listeners, idle connections
			// until context cancel or time-out
			e.cfg.logger.Info(
				"stopping serving peer traffic",
				zap.String("address", u),
			)
			srv.Shutdown(ctx)
			e.cfg.logger.Info(
				"stopped serving peer traffic",
				zap.String("address", u),
			)
			m.Close()
			return nil
		}
	}

	// start peer servers in a goroutine
	for _, pl := range e.Peers {
		l := pl
		e.startHandler(func() error {
			u := l.Addr().String()
			e.cfg.logger.Info(
				"serving peer traffic",
				zap.String("address", u),
			)
			return l.serve()
		})
	}
}

func configureClientListeners(cfg *Config) (sctxs map[string]*serveCtx, err error) {
	if err = updateCipherSuites(&cfg.ClientTLSInfo, cfg.CipherSuites); err != nil {
		return nil, err
	}
	if err = cfg.ClientSelfCert(); err != nil {
		cfg.logger.Fatal("failed to get client self-signed certs", zap.Error(err))
	}
	updateMinMaxVersions(&cfg.ClientTLSInfo, cfg.TlsMinVersion, cfg.TlsMaxVersion)
	if cfg.EnablePprof {
		cfg.logger.Info("pprof is enabled", zap.String("path", debugutil.HTTPPrefixPProf))
	}

	sctxs = make(map[string]*serveCtx)
	for _, u := range append(cfg.ListenClientUrls, cfg.ListenClientHttpUrls...) {
		if u.Scheme == "http" || u.Scheme == "unix" {
			if !cfg.ClientTLSInfo.Empty() {
				cfg.logger.Warn("scheme is http or unix while key and cert files are present; ignoring key and cert files", zap.String("client-url", u.String()))
			}
			if cfg.ClientTLSInfo.ClientCertAuth {
				cfg.logger.Warn("scheme is http or unix while --client-cert-auth is enabled; ignoring client cert auth for this URL", zap.String("client-url", u.String()))
			}
		}
		if (u.Scheme == "https" || u.Scheme == "unixs") && cfg.ClientTLSInfo.Empty() {
			return nil, fmt.Errorf("TLS key/cert (--cert-file, --key-file) must be provided for client url %s with HTTPS scheme", u.String())
		}
	}

	for _, u := range cfg.ListenClientUrls {
		addr, secure, network := resolveURL(u)
		sctx := sctxs[addr]
		if sctx == nil {
			sctx = newServeCtx(cfg.logger)
			sctxs[addr] = sctx
		}
		sctx.secure = sctx.secure || secure
		sctx.insecure = sctx.insecure || !secure
		sctx.scheme = u.Scheme
		sctx.addr = addr
		sctx.network = network
	}
	for _, u := range cfg.ListenClientHttpUrls {
		addr, secure, network := resolveURL(u)

		sctx := sctxs[addr]
		if sctx == nil {
			sctx = newServeCtx(cfg.logger)
			sctxs[addr] = sctx
		} else if !sctx.httpOnly {
			return nil, fmt.Errorf("cannot bind both --listen-client-urls and --listen-client-http-urls on the same url %s", u.String())
		}
		sctx.secure = sctx.secure || secure
		sctx.insecure = sctx.insecure || !secure
		sctx.scheme = u.Scheme
		sctx.addr = addr
		sctx.network = network
		sctx.httpOnly = true
	}

	for _, sctx := range sctxs {
		if sctx.l, err = transport.NewListenerWithOpts(sctx.addr, sctx.scheme,
			transport.WithSocketOpts(&cfg.SocketOpts),
			transport.WithSkipTLSInfoCheck(true),
		); err != nil {
			return nil, err
		}
		// net.Listener will rewrite ipv4 0.0.0.0 to ipv6 [::], breaking
		// hosts that disable ipv6. So, use the address given by the user.

		if fdLimit, fderr := runtimeutil.FDLimit(); fderr == nil {
			if fdLimit <= reservedInternalFDNum {
				cfg.logger.Fatal(
					"file descriptor limit of etcd process is too low; please set higher",
					zap.Uint64("limit", fdLimit),
					zap.Int("recommended-limit", reservedInternalFDNum),
				)
			}
			sctx.l = transport.LimitListener(sctx.l, int(fdLimit-reservedInternalFDNum))
		}

		defer func(sctx *serveCtx) {
			if err == nil || sctx.l == nil {
				return
			}
			sctx.l.Close()
			cfg.logger.Warn(
				"closing peer listener",
				zap.String("address", sctx.addr),
				zap.Error(err),
			)
		}(sctx)
		for k := range cfg.UserHandlers {
			sctx.userHandlers[k] = cfg.UserHandlers[k]
		}
		sctx.serviceRegister = cfg.ServiceRegister
		if cfg.EnablePprof || cfg.LogLevel == "debug" {
			sctx.registerPprof()
		}
		if cfg.LogLevel == "debug" {
			sctx.registerTrace()
		}
	}
	return sctxs, nil
}

func resolveURL(u url.URL) (addr string, secure bool, network string) {
	addr = u.Host
	network = "tcp"
	if u.Scheme == "unix" || u.Scheme == "unixs" {
		addr = u.Host + u.Path
		network = "unix"
	}
	secure = u.Scheme == "https" || u.Scheme == "unixs"
	return addr, secure, network
}

func (e *Etcd) serveClients() {
	if !e.cfg.ClientTLSInfo.Empty() {
		e.cfg.logger.Info(
			"starting with client TLS",
			zap.String("tls-info", fmt.Sprintf("%+v", e.cfg.ClientTLSInfo)),
			zap.Strings("cipher-suites", e.cfg.CipherSuites),
		)
	}

	// Start a client server goroutine for each listen address
	mux := http.NewServeMux()
	etcdhttp.HandleDebug(mux)
	etcdhttp.HandleVersion(mux, e.Server)
	etcdhttp.HandleMetrics(mux)
	etcdhttp.HandleHealth(e.cfg.logger, mux, e.Server)

	var gopts []grpc.ServerOption
	if e.cfg.GRPCKeepAliveMinTime > time.Duration(0) {
		gopts = append(gopts, grpc.KeepaliveEnforcementPolicy(keepalive.EnforcementPolicy{
			MinTime:             e.cfg.GRPCKeepAliveMinTime,
			PermitWithoutStream: false,
		}))
	}
	if e.cfg.GRPCKeepAliveInterval > time.Duration(0) &&
		e.cfg.GRPCKeepAliveTimeout > time.Duration(0) {
		gopts = append(gopts, grpc.KeepaliveParams(keepalive.ServerParameters{
			Time:    e.cfg.GRPCKeepAliveInterval,
			Timeout: e.cfg.GRPCKeepAliveTimeout,
		}))
	}
	gopts = append(gopts, e.cfg.GRPCAdditionalServerOptions...)

	splitHTTP := false
	for _, sctx := range e.sctxs {
		if sctx.httpOnly {
			splitHTTP = true
		}
	}

	// start client servers in each goroutine
	for _, sctx := range e.sctxs {
		s := sctx
		e.startHandler(func() error {
			return s.serve(e.Server, &e.cfg.ClientTLSInfo, mux, e.errHandler, e.grpcGatewayDial(splitHTTP), splitHTTP, gopts...)
		})
	}
}

func (e *Etcd) grpcGatewayDial(splitHTTP bool) (grpcDial func(ctx context.Context) (*grpc.ClientConn, error)) {
	if !e.cfg.EnableGRPCGateway {
		return nil
	}
	sctx := e.pickGRPCGatewayServeContext(splitHTTP)
	addr := sctx.addr
	if network := sctx.network; network == "unix" {
		// explicitly define unix network for gRPC socket support
		addr = fmt.Sprintf("%s:%s", network, addr)
	}
	opts := []grpc.DialOption{grpc.WithDefaultCallOptions(grpc.MaxCallRecvMsgSize(math.MaxInt32))}
	if sctx.secure {
		tlscfg, tlsErr := e.cfg.ClientTLSInfo.ServerConfig()
		if tlsErr != nil {
			return func(ctx context.Context) (*grpc.ClientConn, error) {
				return nil, tlsErr
			}
		}
		dtls := tlscfg.Clone()
		// trust local server
		dtls.InsecureSkipVerify = true
		opts = append(opts, grpc.WithTransportCredentials(credentials.NewTransportCredential(dtls)))
	} else {
		opts = append(opts, grpc.WithTransportCredentials(insecure.NewCredentials()))
	}

	return func(ctx context.Context) (*grpc.ClientConn, error) {
		conn, err := grpc.DialContext(ctx, addr, opts...)
		if err != nil {
			sctx.lg.Error("grpc gateway failed to dial", zap.String("addr", addr), zap.Error(err))
			return nil, err
		}
		return conn, err
	}
}

func (e *Etcd) pickGRPCGatewayServeContext(splitHTTP bool) *serveCtx {
	for _, sctx := range e.sctxs {
		if !splitHTTP || !sctx.httpOnly {
			return sctx
		}
	}
	panic("Expect at least one context able to serve grpc")
}

var ErrMissingClientTLSInfoForMetricsURL = errors.New("client TLS key/cert (--cert-file, --key-file) must be provided for metrics secure url")

func (e *Etcd) createMetricsListener(murl url.URL) (net.Listener, error) {
	tlsInfo := &e.cfg.ClientTLSInfo
	switch murl.Scheme {
	case "http":
		tlsInfo = nil
	case "https", "unixs":
		if e.cfg.ClientTLSInfo.Empty() {
			return nil, ErrMissingClientTLSInfoForMetricsURL
		}
	}
	return transport.NewListenerWithOpts(murl.Host, murl.Scheme,
		transport.WithTLSInfo(tlsInfo),
		transport.WithSocketOpts(&e.cfg.SocketOpts),
	)
}

func (e *Etcd) serveMetrics() (err error) {
	if len(e.cfg.ListenMetricsUrls) > 0 {
		metricsMux := http.NewServeMux()
		etcdhttp.HandleMetrics(metricsMux)
		etcdhttp.HandleHealth(e.cfg.logger, metricsMux, e.Server)

		for _, murl := range e.cfg.ListenMetricsUrls {
			u := murl
			ml, err := e.createMetricsListener(murl)
			if err != nil {
				return err
			}
			e.metricsListeners = append(e.metricsListeners, ml)

			e.startHandler(func() error {
				e.cfg.logger.Info(
					"serving metrics",
					zap.String("address", u.String()),
				)
				return http.Serve(ml, metricsMux)
			})
		}
	}
	return nil
}

func (e *Etcd) startHandler(handler func() error) {
	// start each handler in a separate goroutine
	e.wg.Add(1)
	go func() {
		defer e.wg.Done()
		e.errHandler(handler())
	}()
}

func (e *Etcd) errHandler(err error) {
	if err != nil {
		e.GetLogger().Error("setting up serving from embedded etcd failed.", zap.Error(err))
	}
	select {
	case <-e.stopc:
		return
	default:
	}
	select {
	case <-e.stopc:
	case e.errc <- err:
	}
}

// GetLogger returns the logger.
func (e *Etcd) GetLogger() *zap.Logger {
	e.cfg.loggerMu.RLock()
	l := e.cfg.logger
	e.cfg.loggerMu.RUnlock()
	return l
}

func parseCompactionRetention(mode, retention string) (ret time.Duration, err error) {
	h, err := strconv.Atoi(retention)
	if err == nil && h >= 0 {
		switch mode {
		case CompactorModeRevision:
			ret = time.Duration(int64(h))
		case CompactorModePeriodic:
			ret = time.Duration(int64(h)) * time.Hour
		case "":
			return 0, errors.New("--auto-compaction-mode is undefined")
		}
	} else {
		// periodic compaction
		ret, err = time.ParseDuration(retention)
		if err != nil {
			return 0, fmt.Errorf("error parsing CompactionRetention: %w", err)
		}
	}
	return ret, nil
}