Create a v2 snapshot when running etcdutl migrate command

Also added test to cover the etcdutl migrate command

Signed-off-by: Benjamin Wang <[email protected]>

etcdutl/etcdutl/common.go

@@ -16,14 +16,19 @@ 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"
@@ -68,3 +73,88 @@ func getLatestV2Snapshot(lg *zap.Logger, dataDir string) (*raftpb.Snapshot, erro
 
 	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.UnsafeLoad()
+
+	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.
+	_, st, _, err := w.ReadAll()
+	if err != nil {
+		return err
+	}
+
+	if err := w.SaveSnapshot(walpb.Snapshot{Index: ci, Term: term, ConfState: &confState}); err != nil {
+		return err
+	}
+	if err := w.Save(raftpb.HardState{Term: term, Commit: ci, Vote: st.Vote}, nil); err != nil {
+		return err
+	}
+	return w.Sync()
+}
+
+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
+}