githubmirror/etcd

server/etcdserver/bootstrap.go
749 строк23 KB
Marek Siarkowicz
build: upgrade go.etcd.io/raft to v3.7.0-beta.0
27 май 2026, 17:38
27 май 2026, 17:384715a54
// Copyright 2021 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 (
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"os"
	"strings"
	"time"

	"github.com/coreos/go-semver/semver"
	"github.com/dustin/go-humanize"
	"go.uber.org/zap"
	"google.golang.org/protobuf/proto"

	"go.etcd.io/etcd/api/v3/etcdserverpb"
	"go.etcd.io/etcd/client/pkg/v3/fileutil"
	"go.etcd.io/etcd/client/pkg/v3/types"
	"go.etcd.io/etcd/pkg/v3/pbutil"
	"go.etcd.io/etcd/server/v3/config"
	"go.etcd.io/etcd/server/v3/etcdserver/api"
	"go.etcd.io/etcd/server/v3/etcdserver/api/membership"
	"go.etcd.io/etcd/server/v3/etcdserver/api/rafthttp"
	"go.etcd.io/etcd/server/v3/etcdserver/api/snap"
	"go.etcd.io/etcd/server/v3/etcdserver/api/v3discovery"
	"go.etcd.io/etcd/server/v3/etcdserver/cindex"
	servererrors "go.etcd.io/etcd/server/v3/etcdserver/errors"
	serverstorage "go.etcd.io/etcd/server/v3/storage"
	"go.etcd.io/etcd/server/v3/storage/backend"
	"go.etcd.io/etcd/server/v3/storage/schema"
	"go.etcd.io/etcd/server/v3/storage/wal"
	"go.etcd.io/etcd/server/v3/storage/wal/walpb"
	"go.etcd.io/raft/v3"
	"go.etcd.io/raft/v3/raftpb"
)

func bootstrap(cfg config.ServerConfig) (b *bootstrappedServer, err error) {
	if cfg.MaxRequestBytes > recommendedMaxRequestBytes {
		cfg.Logger.Warn(
			"exceeded recommended request limit",
			zap.Uint("max-request-bytes", cfg.MaxRequestBytes),
			zap.String("max-request-size", humanize.Bytes(uint64(cfg.MaxRequestBytes))),
			zap.Int("recommended-request-bytes", recommendedMaxRequestBytes),
			zap.String("recommended-request-size", recommendedMaxRequestBytesString),
		)
	}

	if terr := fileutil.TouchDirAll(cfg.Logger, cfg.DataDir); terr != nil {
		return nil, fmt.Errorf("cannot access data directory: %w", terr)
	}

	if terr := fileutil.TouchDirAll(cfg.Logger, cfg.MemberDir()); terr != nil {
		return nil, fmt.Errorf("cannot access member directory: %w", terr)
	}
	ss := bootstrapSnapshot(cfg)
	prt, err := rafthttp.NewRoundTripper(cfg.PeerTLSInfo, cfg.PeerDialTimeout())
	if err != nil {
		return nil, err
	}

	haveWAL := wal.Exist(cfg.WALDir())
	backend, err := bootstrapBackend(cfg, haveWAL)
	if err != nil {
		return nil, err
	}
	var bwal *bootstrappedWAL

	if haveWAL {
		if err = fileutil.IsDirWriteable(cfg.WALDir()); err != nil {
			return nil, fmt.Errorf("cannot write to WAL directory: %w", err)
		}
		cfg.Logger.Info("Bootstrapping WAL from snapshot")
		bwal = bootstrapWALFromSnapshot(cfg, backend.snapshot, backend.ci)
	}

	cfg.Logger.Info("bootstrapping cluster")
	cluster, err := bootstrapCluster(cfg, bwal, prt)
	if err != nil {
		backend.Close()
		return nil, err
	}

	cfg.Logger.Info("bootstrapping storage")
	s := bootstrapStorage(cfg, backend, bwal, cluster)

	if err = cluster.Finalize(cfg, s); err != nil {
		backend.Close()
		return nil, err
	}

	if haveWAL {
		sn := s.wal.snapshot
		if sn == nil {
			sn = &raftpb.Snapshot{}
		}
		cs := buildConfStateFromV3store(cfg.Logger, backend.be)

		sn.Metadata.ConfState = &cs
		s.wal.snapshot = sn

		cfg.Logger.Info("Constructed a new raft snapshot from v3 state", zap.Uint64("index", sn.Metadata.GetIndex()),
			zap.Uint64("term", sn.Metadata.GetTerm()), zap.String("confState", sn.Metadata.ConfState.String()))
	}

	cfg.Logger.Info("bootstrapping raft")
	raft := bootstrapRaft(cfg, cluster, s.wal)
	return &bootstrappedServer{
		prt:     prt,
		ss:      ss,
		storage: s,
		cluster: cluster,
		raft:    raft,
	}, nil
}

func buildConfStateFromV3store(lg *zap.Logger, be backend.Backend) raftpb.ConfState {
	members, _ := schema.NewMembershipBackend(lg, be).MustReadMembersFromBackend()
	var (
		voters   []uint64
		learners []uint64
	)
	for _, m := range members {
		if m.IsLearner {
			learners = append(learners, uint64(m.ID))
		} else {
			voters = append(voters, uint64(m.ID))
		}
	}
	return raftpb.ConfState{
		Voters:   voters,
		Learners: learners,
	}
}

type bootstrappedServer struct {
	storage *bootstrappedStorage
	cluster *bootstrappedCluster
	raft    *bootstrappedRaft
	prt     http.RoundTripper
	ss      *snap.Snapshotter
}

func (s *bootstrappedServer) Close() {
	s.storage.Close()
}

type bootstrappedStorage struct {
	backend *bootstrappedBackend
	wal     *bootstrappedWAL
}

func (s *bootstrappedStorage) Close() {
	s.backend.Close()
}

type bootstrappedBackend struct {
	beHooks  *serverstorage.BackendHooks
	be       backend.Backend
	ci       cindex.ConsistentIndexer
	beExist  bool
	snapshot *raftpb.Snapshot
}

func (s *bootstrappedBackend) Close() {
	s.be.Close()
}

type bootstrappedCluster struct {
	remotes []*membership.Member
	cl      *membership.RaftCluster
	nodeID  types.ID
}

type bootstrappedRaft struct {
	lg        *zap.Logger
	heartbeat time.Duration

	peers   []raft.Peer
	config  *raft.Config
	storage *raft.MemoryStorage
}

func bootstrapStorage(cfg config.ServerConfig, be *bootstrappedBackend, wal *bootstrappedWAL, cl *bootstrappedCluster) *bootstrappedStorage {
	if wal == nil {
		wal = bootstrapNewWAL(cfg, cl)
	}

	return &bootstrappedStorage{
		backend: be,
		wal:     wal,
	}
}

func bootstrapSnapshot(cfg config.ServerConfig) *snap.Snapshotter {
	if err := fileutil.TouchDirAll(cfg.Logger, cfg.SnapDir()); err != nil {
		cfg.Logger.Fatal(
			"failed to create snapshot directory",
			zap.String("path", cfg.SnapDir()),
			zap.Error(err),
		)
	}

	if err := fileutil.RemoveMatchFile(cfg.Logger, cfg.SnapDir(), func(fileName string) bool {
		return strings.HasPrefix(fileName, "tmp")
	}); err != nil {
		cfg.Logger.Error(
			"failed to remove temp file(s) in snapshot directory",
			zap.String("path", cfg.SnapDir()),
			zap.Error(err),
		)
	}
	return snap.New(cfg.Logger, cfg.SnapDir())
}

func bootstrapBackend(cfg config.ServerConfig, haveWAL bool) (backend *bootstrappedBackend, err error) {
	beExist := fileutil.Exist(cfg.BackendPath())
	ci := cindex.NewConsistentIndex(nil)
	beHooks := serverstorage.NewBackendHooks(cfg.Logger, ci)
	be := serverstorage.OpenBackend(cfg, beHooks)
	defer func() {
		if err != nil && be != nil {
			be.Close()
		}
	}()
	ci.SetBackend(be)
	schema.CreateMetaBucket(be.BatchTx())
	if cfg.BootstrapDefragThresholdMegabytes != 0 {
		err = maybeDefragBackend(cfg, be)
		if err != nil {
			return nil, err
		}
	}
	cfg.Logger.Info("restore consistentIndex", zap.Uint64("index", ci.ConsistentIndex()))

	// TODO(serathius): Implement schema setup in fresh storage
	var snapshot *raftpb.Snapshot
	if haveWAL {
		snapshot, be, err = recoverSnapshot(cfg, be, beExist, beHooks, ci)
		if err != nil {
			return nil, err
		}
	}
	if beExist {
		s1, s2 := be.Size(), be.SizeInUse()
		cfg.Logger.Info(
			"recovered v3 backend",
			zap.Int64("backend-size-bytes", s1),
			zap.String("backend-size", humanize.Bytes(uint64(s1))),
			zap.Int64("backend-size-in-use-bytes", s2),
			zap.String("backend-size-in-use", humanize.Bytes(uint64(s2))),
		)
		if err = schema.Validate(cfg.Logger, be.ReadTx()); err != nil {
			cfg.Logger.Error("Failed to validate schema", zap.Error(err))
			return nil, err
		}
	}

	return &bootstrappedBackend{
		beHooks:  beHooks,
		be:       be,
		ci:       ci,
		beExist:  beExist,
		snapshot: snapshot,
	}, nil
}

func maybeDefragBackend(cfg config.ServerConfig, be backend.Backend) error {
	size := be.Size()
	sizeInUse := be.SizeInUse()
	freeableMemory := uint(size - sizeInUse)
	thresholdBytes := cfg.BootstrapDefragThresholdMegabytes * 1024 * 1024
	if freeableMemory < thresholdBytes {
		cfg.Logger.Info("Skipping defragmentation",
			zap.Int64("current-db-size-bytes", size),
			zap.String("current-db-size", humanize.Bytes(uint64(size))),
			zap.Int64("current-db-size-in-use-bytes", sizeInUse),
			zap.String("current-db-size-in-use", humanize.Bytes(uint64(sizeInUse))),
			zap.Uint("bootstrap-defrag-threshold-bytes", thresholdBytes),
			zap.String("bootstrap-defrag-threshold", humanize.Bytes(uint64(thresholdBytes))),
		)
		return nil
	}
	return be.Defrag()
}

func bootstrapCluster(cfg config.ServerConfig, bwal *bootstrappedWAL, prt http.RoundTripper) (c *bootstrappedCluster, err error) {
	switch {
	case bwal == nil && !cfg.NewCluster:
		c, err = bootstrapExistingClusterNoWAL(cfg, prt)
	case bwal == nil && cfg.NewCluster:
		c, err = bootstrapNewClusterNoWAL(cfg, prt)
	case bwal != nil && bwal.haveWAL:
		c, err = bootstrapClusterWithWAL(cfg, bwal.meta)
	default:
		return nil, fmt.Errorf("unsupported bootstrap config")
	}
	if err != nil {
		return nil, err
	}
	return c, nil
}

func bootstrapExistingClusterNoWAL(cfg config.ServerConfig, prt http.RoundTripper) (*bootstrappedCluster, error) {
	if err := cfg.VerifyJoinExisting(); err != nil {
		return nil, err
	}
	cl, err := membership.NewClusterFromURLsMap(cfg.Logger, cfg.InitialClusterToken, cfg.InitialPeerURLsMap, membership.WithMaxLearners(cfg.MaxLearners))
	if err != nil {
		return nil, err
	}
	existingCluster, gerr := GetClusterFromRemotePeers(cfg.Logger, getRemotePeerURLs(cl, cfg.Name), prt)
	if gerr != nil {
		return nil, fmt.Errorf("cannot fetch cluster info from peer urls: %w", gerr)
	}
	if err := membership.ValidateClusterAndAssignIDs(cfg.Logger, cl, existingCluster); err != nil {
		return nil, fmt.Errorf("error validating peerURLs %s: %w", existingCluster, err)
	}
	if !isCompatibleWithCluster(cfg.Logger, cl, cl.MemberByName(cfg.Name).ID, prt, cfg.ReqTimeout()) {
		return nil, fmt.Errorf("incompatible with current running cluster")
	}
	scaleUpLearners := false
	if err := membership.ValidateMaxLearnerConfig(cfg.MaxLearners, existingCluster.Members(), scaleUpLearners); err != nil {
		return nil, err
	}
	remotes := existingCluster.Members()
	cl.SetID(types.ID(0), existingCluster.ID())
	member := cl.MemberByName(cfg.Name)
	return &bootstrappedCluster{
		remotes: remotes,
		cl:      cl,
		nodeID:  member.ID,
	}, nil
}

func bootstrapNewClusterNoWAL(cfg config.ServerConfig, prt http.RoundTripper) (*bootstrappedCluster, error) {
	if err := cfg.VerifyBootstrap(); err != nil {
		return nil, err
	}
	cl, err := membership.NewClusterFromURLsMap(cfg.Logger, cfg.InitialClusterToken, cfg.InitialPeerURLsMap, membership.WithMaxLearners(cfg.MaxLearners))
	if err != nil {
		return nil, err
	}
	m := cl.MemberByName(cfg.Name)
	if isMemberBootstrapped(cfg.Logger, cl, cfg.Name, prt, cfg.BootstrapTimeoutEffective()) {
		return nil, fmt.Errorf("member %s has already been bootstrapped", m.ID)
	}
	if cfg.ShouldDiscover() {
		cfg.Logger.Info("Bootstrapping cluster using v3 discovery.")
		str, err := v3discovery.JoinCluster(cfg.Logger, &cfg.DiscoveryCfg, m.ID, cfg.InitialPeerURLsMap.String())
		if err != nil {
			return nil, &servererrors.DiscoveryError{Op: "join", Err: err}
		}
		var urlsmap types.URLsMap
		urlsmap, err = types.NewURLsMap(str)
		if err != nil {
			return nil, err
		}
		if config.CheckDuplicateURL(urlsmap) {
			return nil, fmt.Errorf("discovery cluster %s has duplicate url", urlsmap)
		}
		if cl, err = membership.NewClusterFromURLsMap(cfg.Logger, cfg.InitialClusterToken, urlsmap, membership.WithMaxLearners(cfg.MaxLearners)); err != nil {
			return nil, err
		}
	}
	return &bootstrappedCluster{
		remotes: nil,
		cl:      cl,
		nodeID:  m.ID,
	}, nil
}

func bootstrapClusterWithWAL(cfg config.ServerConfig, meta *snapshotMetadata) (*bootstrappedCluster, error) {
	if err := fileutil.IsDirWriteable(cfg.MemberDir()); err != nil {
		return nil, fmt.Errorf("cannot write to member directory: %w", err)
	}

	if cfg.ShouldDiscover() {
		cfg.Logger.Warn(
			"discovery token is ignored since cluster already initialized; valid logs are found",
			zap.String("wal-dir", cfg.WALDir()),
		)
	}
	cl := membership.NewCluster(cfg.Logger, membership.WithMaxLearners(cfg.MaxLearners))

	scaleUpLearners := false
	if err := membership.ValidateMaxLearnerConfig(cfg.MaxLearners, cl.Members(), scaleUpLearners); err != nil {
		return nil, err
	}

	cl.SetID(meta.nodeID, meta.clusterID)
	return &bootstrappedCluster{
		cl:     cl,
		nodeID: meta.nodeID,
	}, nil
}

func recoverSnapshot(cfg config.ServerConfig, be backend.Backend, beExist bool, beHooks *serverstorage.BackendHooks, ci cindex.ConsistentIndexer) (*raftpb.Snapshot, backend.Backend, error) {
	// Find a snapshot to start/restart a raft node
	walSnaps, err := wal.ValidSnapshotEntries(cfg.Logger, cfg.WALDir())
	if err != nil {
		return nil, be, err
	}

	var snapshot *raftpb.Snapshot
	if len(walSnaps) > 0 {
		idx := len(walSnaps) - 1
		snapshot = &raftpb.Snapshot{
			Metadata: &raftpb.SnapshotMetadata{
				Term:  new(walSnaps[idx].GetTerm()),
				Index: new(walSnaps[idx].GetIndex()),
			},
		}
		if walSnaps[idx].ConfState != nil {
			snapshot.Metadata.ConfState = proto.Clone(walSnaps[idx].ConfState).(*raftpb.ConfState)
		}
		cfg.Logger.Info("constructed a snapshot from WAL record",
			zap.Uint64("snapshot-index", snapshot.Metadata.GetIndex()),
			zap.Int("snapshot-size", proto.Size(snapshot)),
			zap.String("confState", snapshot.Metadata.ConfState.String()),
			zap.Int("walSnaps-count", len(walSnaps)),
		)
	}

	if snapshot != nil {
		if be, err = serverstorage.RecoverSnapshotBackend(cfg, be, snapshot, beExist, beHooks); err != nil {
			cfg.Logger.Panic("failed to recover v3 backend from snapshot", zap.Error(err))
		}
		// A snapshot db may have already been recovered, and the old db should have
		// already been closed in this case, so we should set the backend again.
		ci.SetBackend(be)

		if beExist {
			// TODO: remove kvindex != 0 checking when we do not expect users to upgrade
			// etcd from pre-3.0 release.
			kvindex := ci.ConsistentIndex()
			if kvindex < snapshot.Metadata.GetIndex() {
				if kvindex != 0 {
					return nil, be, fmt.Errorf("database file (%v index %d) does not match with snapshot (index %d)", cfg.BackendPath(), kvindex, snapshot.Metadata.GetIndex())
				}
				cfg.Logger.Warn(
					"consistent index was never saved",
					zap.Uint64("snapshot-index", snapshot.Metadata.GetIndex()),
				)
			}
		}
	} else {
		cfg.Logger.Info("No snapshot found. Recovering WAL from scratch!")
	}
	return snapshot, be, nil
}

func (c *bootstrappedCluster) Finalize(cfg config.ServerConfig, s *bootstrappedStorage) error {
	if !s.wal.haveWAL {
		c.cl.SetID(c.nodeID, c.cl.ID())
	}
	c.cl.SetBackend(schema.NewMembershipBackend(cfg.Logger, s.backend.be))
	if s.wal.haveWAL {
		c.cl.Recover(api.UpdateCapability)
		if c.databaseFileMissing(s) {
			bepath := cfg.BackendPath()
			os.RemoveAll(bepath)
			return fmt.Errorf("database file (%v) of the backend is missing", bepath)
		}
	}
	scaleUpLearners := false
	return membership.ValidateMaxLearnerConfig(cfg.MaxLearners, c.cl.Members(), scaleUpLearners)
}

func (c *bootstrappedCluster) databaseFileMissing(s *bootstrappedStorage) bool {
	v3Cluster := c.cl.Version() != nil && !c.cl.Version().LessThan(semver.Version{Major: 3})
	return v3Cluster && !s.backend.beExist
}

func bootstrapRaft(cfg config.ServerConfig, cluster *bootstrappedCluster, bwal *bootstrappedWAL) *bootstrappedRaft {
	switch {
	case !bwal.haveWAL && !cfg.NewCluster:
		return bootstrapRaftFromCluster(cfg, cluster.cl, nil, bwal)
	case !bwal.haveWAL && cfg.NewCluster:
		return bootstrapRaftFromCluster(cfg, cluster.cl, cluster.cl.MemberIDs(), bwal)
	case bwal.haveWAL:
		return bootstrapRaftFromWAL(cfg, bwal)
	default:
		cfg.Logger.Panic("unsupported bootstrap config")
		return nil
	}
}

func bootstrapRaftFromCluster(cfg config.ServerConfig, cl *membership.RaftCluster, ids []types.ID, bwal *bootstrappedWAL) *bootstrappedRaft {
	member := cl.MemberByName(cfg.Name)
	peers := make([]raft.Peer, len(ids))
	for i, id := range ids {
		var ctx []byte
		ctx, err := json.Marshal((*cl).Member(id))
		if err != nil {
			cfg.Logger.Panic("failed to marshal member", zap.Error(err))
		}
		peers[i] = raft.Peer{ID: uint64(id), Context: ctx}
	}
	cfg.Logger.Info(
		"starting local member",
		zap.String("local-member-id", member.ID.String()),
		zap.String("cluster-id", cl.ID().String()),
	)
	s := bwal.MemoryStorage()
	return &bootstrappedRaft{
		lg:        cfg.Logger,
		heartbeat: time.Duration(cfg.TickMs) * time.Millisecond,
		config:    raftConfig(cfg, uint64(member.ID), s),
		peers:     peers,
		storage:   s,
	}
}

func bootstrapRaftFromWAL(cfg config.ServerConfig, bwal *bootstrappedWAL) *bootstrappedRaft {
	s := bwal.MemoryStorage()
	return &bootstrappedRaft{
		lg:        cfg.Logger,
		heartbeat: time.Duration(cfg.TickMs) * time.Millisecond,
		config:    raftConfig(cfg, uint64(bwal.meta.nodeID), s),
		storage:   s,
	}
}

func raftConfig(cfg config.ServerConfig, id uint64, s *raft.MemoryStorage) *raft.Config {
	return &raft.Config{
		ID:              id,
		ElectionTick:    cfg.ElectionTicks,
		HeartbeatTick:   1,
		Storage:         s,
		MaxSizePerMsg:   maxSizePerMsg,
		MaxInflightMsgs: maxInflightMsgs,
		CheckQuorum:     true,
		PreVote:         cfg.PreVote,
		Logger:          NewRaftLoggerZap(cfg.Logger.Named("raft")),
	}
}

func (b *bootstrappedRaft) newRaftNode(ss *snap.Snapshotter, wal *wal.WAL, cl *membership.RaftCluster) *raftNode {
	var n raft.Node
	if len(b.peers) == 0 {
		n = raft.RestartNode(b.config)
	} else {
		n = raft.StartNode(b.config, b.peers)
	}
	raftStatusMu.Lock()
	raftStatus = n.Status
	raftStatusMu.Unlock()
	return newRaftNode(
		raftNodeConfig{
			lg:          b.lg,
			isIDRemoved: func(id uint64) bool { return cl.IsIDRemoved(types.ID(id)) },
			Node:        n,
			heartbeat:   b.heartbeat,
			raftStorage: b.storage,
			storage:     serverstorage.NewStorage(b.lg, wal, ss),
		},
	)
}

func bootstrapWALFromSnapshot(cfg config.ServerConfig, snapshot *raftpb.Snapshot, ci cindex.ConsistentIndexer) *bootstrappedWAL {
	wal, st, ents, snap, meta := openWALFromSnapshot(cfg, snapshot)
	bwal := &bootstrappedWAL{
		lg:       cfg.Logger,
		w:        wal,
		st:       st,
		ents:     ents,
		snapshot: snap,
		meta:     meta,
		haveWAL:  true,
	}

	if cfg.ForceNewCluster {
		consistentIndex := ci.ConsistentIndex()
		oldCommitIndex := bwal.st.GetCommit()
		// If only `HardState.Commit` increases, HardState won't be persisted
		// to disk, even though the committed entries might have already been
		// applied. This can result in consistent_index > CommitIndex.
		//
		// When restarting etcd with `--force-new-cluster`, all uncommitted
		// entries are dropped. To avoid losing entries that were actually
		// committed, we reset Commit to max(HardState.Commit, consistent_index).
		//
		// See: https://github.com/etcd-io/raft/pull/300 for more details.
		bwal.st.Commit = new(max(oldCommitIndex, consistentIndex))

		// discard the previously uncommitted entries
		bwal.ents = bwal.CommitedEntries()
		entries := bwal.NewConfigChangeEntries()
		// force commit config change entries
		bwal.AppendAndCommitEntries(entries)
		cfg.Logger.Info(
			"forcing restart member",
			zap.String("cluster-id", meta.clusterID.String()),
			zap.String("local-member-id", meta.nodeID.String()),
			zap.Uint64("wal-commit-index", oldCommitIndex),
			zap.Uint64("commit-index", bwal.st.GetCommit()),
		)
	} else {
		cfg.Logger.Info(
			"restarting local member",
			zap.String("cluster-id", meta.clusterID.String()),
			zap.String("local-member-id", meta.nodeID.String()),
			zap.Uint64("commit-index", bwal.st.GetCommit()),
		)
	}
	return bwal
}

// openWALFromSnapshot reads the WAL at the given snap and returns the wal, its latest HardState and cluster ID, and all entries that appear
// after the position of the given snap in the WAL.
// The snap must have been previously saved to the WAL, or this call will panic.
func openWALFromSnapshot(cfg config.ServerConfig, snapshot *raftpb.Snapshot) (*wal.WAL, *raftpb.HardState, []*raftpb.Entry, *raftpb.Snapshot, *snapshotMetadata) {
	var walsnap walpb.Snapshot
	if snapshot != nil {
		walsnap.Index, walsnap.Term = new(snapshot.Metadata.GetIndex()), new(snapshot.Metadata.GetTerm())
	}
	repaired := false
	for {
		w, err := wal.Open(cfg.Logger, cfg.WALDir(), &walsnap)
		if err != nil {
			cfg.Logger.Fatal("failed to open WAL", zap.Error(err))
		}
		if cfg.UnsafeNoFsync {
			w.SetUnsafeNoFsync()
		}
		wmetadata, st, ents, err := w.ReadAll()
		if err != nil {
			w.Close()
			// we can only repair ErrUnexpectedEOF and we never repair twice.
			if repaired || !errors.Is(err, io.ErrUnexpectedEOF) {
				cfg.Logger.Fatal("failed to read WAL, cannot be repaired", zap.Error(err))
			}
			if !wal.Repair(cfg.Logger, cfg.WALDir()) {
				cfg.Logger.Fatal("failed to repair WAL", zap.Error(err))
			} else {
				cfg.Logger.Info("repaired WAL", zap.Error(err))
				repaired = true
			}
			continue
		}
		var metadata etcdserverpb.Metadata
		pbutil.MustUnmarshalMessage(&metadata, wmetadata)
		id := types.ID(metadata.GetNodeID())
		cid := types.ID(metadata.GetClusterID())
		meta := &snapshotMetadata{clusterID: cid, nodeID: id}
		return w, st, ents, snapshot, meta
	}
}

type snapshotMetadata struct {
	nodeID, clusterID types.ID
}

func bootstrapNewWAL(cfg config.ServerConfig, cl *bootstrappedCluster) *bootstrappedWAL {
	metadata := pbutil.MustMarshalMessage(
		&etcdserverpb.Metadata{
			NodeID:    new(uint64(cl.nodeID)),
			ClusterID: new(uint64(cl.cl.ID())),
		},
	)
	w, err := wal.Create(cfg.Logger, cfg.WALDir(), metadata)
	if err != nil {
		cfg.Logger.Panic("failed to create WAL", zap.Error(err))
	}
	if cfg.UnsafeNoFsync {
		w.SetUnsafeNoFsync()
	}
	return &bootstrappedWAL{
		lg: cfg.Logger,
		w:  w,
	}
}

type bootstrappedWAL struct {
	lg *zap.Logger

	haveWAL  bool
	w        *wal.WAL
	st       *raftpb.HardState
	ents     []*raftpb.Entry
	snapshot *raftpb.Snapshot
	meta     *snapshotMetadata
}

func (wal *bootstrappedWAL) MemoryStorage() *raft.MemoryStorage {
	s := raft.NewMemoryStorage()
	if wal.snapshot != nil {
		s.ApplySnapshot(wal.snapshot)
	}
	if wal.st != nil {
		s.SetHardState(wal.st)
	}
	if len(wal.ents) != 0 {
		s.Append(wal.ents)
	}
	return s
}

func (wal *bootstrappedWAL) CommitedEntries() []*raftpb.Entry {
	for i, ent := range wal.ents {
		if ent.GetIndex() > wal.st.GetCommit() {
			wal.lg.Info(
				"discarding uncommitted WAL entries",
				zap.Uint64("entry-index", ent.GetIndex()),
				zap.Uint64("commit-index-from-wal", wal.st.GetCommit()),
				zap.Int("number-of-discarded-entries", len(wal.ents)-i),
			)
			return wal.ents[:i]
		}
	}
	return wal.ents
}

func (wal *bootstrappedWAL) NewConfigChangeEntries() []*raftpb.Entry {
	return serverstorage.CreateConfigChangeEnts(
		wal.lg,
		serverstorage.GetEffectiveNodeIDsFromWALEntries(wal.lg, wal.snapshot, wal.ents),
		uint64(wal.meta.nodeID),
		wal.st.GetTerm(),
		wal.st.GetCommit(),
	)
}

func (wal *bootstrappedWAL) AppendAndCommitEntries(ents []*raftpb.Entry) {
	wal.ents = append(wal.ents, ents...)
	err := wal.w.Save(&raftpb.HardState{}, ents)
	if err != nil {
		wal.lg.Fatal("failed to save hard state and entries", zap.Error(err))
	}
	if len(wal.ents) != 0 {
		wal.st.Commit = wal.ents[len(wal.ents)-1].Index
	}
}