Create a v2 snapshot when running etcdutl migrate command

etcdutl/ctl.go

@@ -45,6 +45,7 @@
 		etcdutl.NewVersionCommand(),
 		etcdutl.NewCompletionCommand(),
 		etcdutl.NewMigrateCommand(),
+		etcdutl.NewV2SnapshotCommand(), // TODO: remove in 3.8
 	)
 }
 

etcdutl/etcdutl/common.go

@@ -15,11 +15,23 @@
 package etcdutl
 
 import (
+	"errors"
+	"fmt"
+
 	"go.uber.org/zap"
 	"go.uber.org/zap/zapcore"
 
 	"go.etcd.io/etcd/client/pkg/v3/logutil"
 	"go.etcd.io/etcd/pkg/v3/cobrautl"
+	"go.etcd.io/etcd/server/v3/etcdserver"
+	"go.etcd.io/etcd/server/v3/etcdserver/api/membership"
+	"go.etcd.io/etcd/server/v3/etcdserver/api/snap"
+	"go.etcd.io/etcd/server/v3/storage/backend"
+	"go.etcd.io/etcd/server/v3/storage/datadir"
+	"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/raftpb"
 )
 
 func GetLogger() *zap.Logger {
@@ -32,3 +44,110 @@
 	}
 	return lg
 }
+
+func getLatestWALSnap(lg *zap.Logger, dataDir string) (walpb.Snapshot, error) {
+	snapshot, err := getLatestV2Snapshot(lg, dataDir)
+	if err != nil {
+		return walpb.Snapshot{}, err
+	}
+
+	var walsnap walpb.Snapshot
+	if snapshot != nil {
+		walsnap.Index, walsnap.Term = snapshot.Metadata.Index, snapshot.Metadata.Term
+	}
+	return walsnap, nil
+}
+
+func getLatestV2Snapshot(lg *zap.Logger, dataDir string) (*raftpb.Snapshot, error) {
+	walPath := datadir.ToWALDir(dataDir)
+	walSnaps, err := wal.ValidSnapshotEntries(lg, walPath)
+	if err != nil {
+		return nil, err
+	}
+
+	ss := snap.New(lg, datadir.ToSnapDir(dataDir))
+	snapshot, err := ss.LoadNewestAvailable(walSnaps)
+	if err != nil && !errors.Is(err, snap.ErrNoSnapshot) {
+		return nil, err
+	}
+
+	return snapshot, nil
+}
+
+func createV2SnapshotFromV3Store(dataDir string, be backend.Backend) error {
+	var (
+		lg = GetLogger()
+
+		snapDir = datadir.ToSnapDir(dataDir)
+		walDir  = datadir.ToWALDir(dataDir)
+	)
+
+	ci, term := schema.ReadConsistentIndex(be.ReadTx())
+
+	cl := membership.NewCluster(lg)
+	cl.SetBackend(schema.NewMembershipBackend(lg, be))
+	cl.Load()
+
+	latestWALSnap, err := getLatestWALSnap(lg, dataDir)
+	if err != nil {
+		return err
+	}
+
+	// Each time before creating the v2 snapshot, etcdserve always flush
+	// the backend storage (bbolt db), so the consistent index should never
+	// less than the Index or term of the latest snapshot.
+	if ci < latestWALSnap.Index || term < latestWALSnap.Term {
+		// This should never happen
+		return fmt.Errorf("consistent_index [Index: %d, Term: %d] is less than the latest snapshot [Index: %d, Term: %d]", ci, term, latestWALSnap.Index, latestWALSnap.Term)
+	}
+
+	voters, learners := getVotersAndLearners(cl)
+	confState := raftpb.ConfState{
+		Voters:   voters,
+		Learners: learners,
+	}
+
+	// create the v2 snaspshot file
+	raftSnap := raftpb.Snapshot{
+		Data: etcdserver.GetMembershipInfoInV2Format(lg, cl),
+		Metadata: raftpb.SnapshotMetadata{
+			Index:     ci,
+			Term:      term,
+			ConfState: confState,
+		},
+	}
+	sn := snap.New(lg, snapDir)
+	if err = sn.SaveSnap(raftSnap); err != nil {
+		return err
+	}
+
+	// save WAL snapshot record
+	w, err := wal.Open(lg, walDir, latestWALSnap)
+	if err != nil {
+		return err
+	}
+	defer w.Close()
+	// We must read all records to locate the tail of the last valid WAL file.
+	if _, _, _, err = w.ReadAll(); err != nil {
+		return err
+	}
+
+	return w.SaveSnapshot(walpb.Snapshot{Index: ci, Term: term, ConfState: &confState})
+}
+
+func getVotersAndLearners(cl *membership.RaftCluster) ([]uint64, []uint64) {
+	var (
+		voters   []uint64
+		learners []uint64
+	)
+	for _, m := range cl.Members() {
+		if m.IsLearner {
+			learners = append(learners, uint64(m.ID))
+			continue
+		}
+
+		voters = append(voters, uint64(m.ID))
+	}
+
+	return voters, learners
+}

etcdutl/etcdutl/migrate_command.go

@@ -15,7 +15,6 @@
 package etcdutl
 
 import (
-	"errors"
 	"fmt"
 	"strings"
 
@@ -25,12 +24,10 @@
 
 	"go.etcd.io/etcd/api/v3/version"
 	"go.etcd.io/etcd/pkg/v3/cobrautl"
-	"go.etcd.io/etcd/server/v3/etcdserver/api/snap"
 	"go.etcd.io/etcd/server/v3/storage/backend"
 	"go.etcd.io/etcd/server/v3/storage/datadir"
 	"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"
 )
 
 // NewMigrateCommand prints out the version of etcd.
@@ -77,8 +74,9 @@
 
 func (o *migrateOptions) Config() (*migrateConfig, error) {
 	c := &migrateConfig{
-		force: o.force,
-		lg:    GetLogger(),
+		force:   o.force,
+		dataDir: o.dataDir,
+		lg:      GetLogger(),
 	}
 	var err error
 	dotCount := strings.Count(o.targetVersion, ".")
@@ -93,67 +91,69 @@
 		return nil, fmt.Errorf(`target version %q not supported. Minimal "3.5"`, storageVersionToString(c.targetVersion))
 	}
 
-	dbPath := datadir.ToBackendFileName(o.dataDir)
-	c.be = backend.NewDefaultBackend(GetLogger(), dbPath)
+	return c, nil
+}
 
-	walPath := datadir.ToWALDir(o.dataDir)
-	walSnap, err := getLatestWALSnap(c.lg, o.dataDir)
+type migrateConfig struct {
+	lg            *zap.Logger
+	be            backend.Backend
+	targetVersion *semver.Version
+	walVersion    schema.WALVersion
+	dataDir       string
+	force         bool
+}
+
+func (c *migrateConfig) finalize() error {
+	walPath := datadir.ToWALDir(c.dataDir)
+	walSnap, err := getLatestWALSnap(c.lg, c.dataDir)
 	if err != nil {
-		return nil, fmt.Errorf("failed to get the lastest snapshot: %w", err)
+		return fmt.Errorf("failed to get the lastest snapshot: %w", err)
 	}
 	w, err := wal.OpenForRead(c.lg, walPath, walSnap)
 	if err != nil {
-		return nil, fmt.Errorf(`failed to open wal: %w`, err)
+		return fmt.Errorf(`failed to open wal: %w`, err)
 	}
 	defer w.Close()
 	c.walVersion, err = wal.ReadWALVersion(w)
 	if err != nil {
-		return nil, fmt.Errorf(`failed to read wal: %w`, err)
-	}
-
-	return c, nil
-}
-
-func getLatestWALSnap(lg *zap.Logger, dataDir string) (walpb.Snapshot, error) {
-	walPath := datadir.ToWALDir(dataDir)
-	walSnaps, err := wal.ValidSnapshotEntries(lg, walPath)
-	if err != nil {
-		return walpb.Snapshot{}, err
-	}
-
-	ss := snap.New(lg, datadir.ToSnapDir(dataDir))
-	snapshot, err := ss.LoadNewestAvailable(walSnaps)
-	if err != nil && !errors.Is(err, snap.ErrNoSnapshot) {
-		return walpb.Snapshot{}, err
-	}
-
-	var walsnap walpb.Snapshot
-	if snapshot != nil {
-		walsnap.Index, walsnap.Term = snapshot.Metadata.Index, snapshot.Metadata.Term
+		return fmt.Errorf(`failed to read wal: %w`, err)
 	}
-	return walsnap, nil
-}
 
-type migrateConfig struct {
-	lg            *zap.Logger
-	be            backend.Backend
-	targetVersion *semver.Version
-	walVersion    schema.WALVersion
-	force         bool
+	return nil
 }
 
 func migrateCommandFunc(c *migrateConfig) error {
+	dbPath := datadir.ToBackendFileName(c.dataDir)
+	c.be = backend.NewDefaultBackend(GetLogger(), dbPath)
 	defer c.be.Close()
+
 	tx := c.be.BatchTx()
 	current, err := schema.DetectSchemaVersion(c.lg, c.be.ReadTx())
 	if err != nil {
-		c.lg.Error("failed to detect storage version. Please make sure you are using data dir from etcd v3.5 and older")
+		c.lg.Error("failed to detect storage version. Please make sure you are using data dir from etcd v3.5 and older", zap.Error(err))
 		return err
 	}
 	if current == *c.targetVersion {
 		c.lg.Info("storage version up-to-date", zap.String("storage-version", storageVersionToString(&current)))
 		return nil
 	}
+
+	// Update cluster version
+	be := schema.NewMembershipBackend(c.lg, c.be)
+	be.MustSaveClusterVersionToBackend(c.targetVersion)
+
+	// forcibly create a v2 snapshot file
+	// TODO: remove in 3.8
+	if err = createV2SnapshotFromV3Store(c.dataDir, c.be); err != nil {
+		c.lg.Error("Failed to create v2 snapshot file", zap.Error(err))
+		return err
+	}
+
+	if err = c.finalize(); err != nil {
+		c.lg.Error("Failed to finalize config", zap.Error(err))
+		return err
+	}
+
 	err = schema.Migrate(c.lg, tx, c.walVersion, *c.targetVersion)
 	if err != nil {
 		if !c.force {
@@ -162,7 +162,9 @@
 		c.lg.Info("normal migrate failed, trying with force", zap.Error(err))
 		migrateForce(c.lg, tx, c.targetVersion)
 	}
+
 	c.be.ForceCommit()
+
 	return nil
 }
 

etcdutl/etcdutl/v2snapshot_command.go

@@ -0,0 +1,61 @@
+// Copyright 2025 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 etcdutl
+
+import (
+	"fmt"
+	"path/filepath"
+
+	"github.com/spf13/cobra"
+
+	"go.etcd.io/etcd/pkg/v3/cobrautl"
+	"go.etcd.io/etcd/server/v3/storage/backend"
+	"go.etcd.io/etcd/server/v3/storage/datadir"
+)
+
+var createV2SnapDataDir string
+
+// NewV2SnapshotCommand returns the cobra command for "v2snapshot".
+// TODO: remove the command in 3.8
+func NewV2SnapshotCommand() *cobra.Command {
+	cmd := &cobra.Command{
+		Use:   "v2snapshot <subcommand>",
+		Short: "Manages etcd node v2snapshots",
+	}
+	cmd.AddCommand(newV2SnapshotCreateCommand())
+	return cmd
+}
+
+func newV2SnapshotCreateCommand() *cobra.Command {
+	cmd := &cobra.Command{
+		Use:   "create",
+		Short: "Create a new v2 snapshot file",
+		Run:   v2SnapshotCreateFunc,
+	}
+	cmd.Flags().StringVar(&createV2SnapDataDir, "data-dir", "", "Required. Path to the etcd data directory.")
+	cmd.MarkFlagRequired("data-dir")
+	cmd.MarkFlagDirname("data-dir")
+	return cmd
+}
+
+func v2SnapshotCreateFunc(_ *cobra.Command, _ []string) {
+	be := backend.NewDefaultBackend(GetLogger(), filepath.Join(datadir.ToSnapDir(createV2SnapDataDir), "db"))
+	defer be.Close()
+
+	if err := createV2SnapshotFromV3Store(createV2SnapDataDir, be); err != nil {
+		cobrautl.ExitWithError(cobrautl.ExitError, err)
+	}
+	fmt.Println("Created a v2 snapshot file.")
+}

server/etcdserver/api/membership/cluster.go

@@ -256,22 +256,28 @@ func (c *RaftCluster) SetVersionChangedNotifier(n *notify.Notifier) {
 	c.versionChanged = n
 }
 
-func (c *RaftCluster) Recover(onSet func(*zap.Logger, *semver.Version)) {
-	c.Lock()
-	defer c.Unlock()
-
+func (c *RaftCluster) Load() {
 	if c.be != nil {
 		c.version = c.be.ClusterVersionFromBackend()
 		c.members, c.removed = c.be.MustReadMembersFromBackend()
 	} else {
 		c.version = clusterVersionFromStore(c.lg, c.v2store)
 		c.members, c.removed = membersFromStore(c.lg, c.v2store)
 	}
-	c.buildMembershipMetric()
 
 	if c.be != nil {
 		c.downgradeInfo = c.be.DowngradeInfoFromBackend()
 	}
+}
+
+func (c *RaftCluster) Recover(onSet func(*zap.Logger, *semver.Version)) {
+	c.Lock()
+	defer c.Unlock()
+
+	c.Load()
+
+	c.buildMembershipMetric()
+
 	sv := semver.Must(semver.NewVersion(version.Version))
 	if c.downgradeInfo != nil && c.downgradeInfo.Enabled {
 		c.lg.Info(