use v2 api to update cluster version

server/etcdserver/apply_v2.go

@@ -21,7 +21,9 @@ import (
 	"strconv"
 	"time"
 
+	"github.com/coreos/go-semver/semver"
 	"go.etcd.io/etcd/pkg/v3/pbutil"
+	"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/v2store"
 
@@ -92,9 +94,12 @@ func (a *applierV2store) Put(r *RequestV2) Response {
 			// return an empty response since there is no consumer.
 			return Response{}
 		}
-		// remove v2 version set to avoid the conflict between v2 and v3.
+		// TODO remove v2 version set to avoid the conflict between v2 and v3 in etcd 3.6
 		if r.Path == membership.StoreClusterVersionKey() {
-			// return an empty response since there is no consumer.
+			if a.cluster != nil {
+				// persist to backend given v2store can be very stale
+				a.cluster.SetVersion(semver.Must(semver.NewVersion(r.Val)), api.UpdateCapability, membership.ApplyBoth)
+			}
 			return Response{}
 		}
 		return toResponse(a.store.Set(r.Path, r.Dir, r.Val, ttlOptions))

server/etcdserver/server.go

@@ -2428,6 +2428,7 @@ func (s *EtcdServer) ClusterVersion() *semver.Version {
 // It updates the cluster version if all members agrees on a higher one.
 // It prints out log if there is a member with a higher version than the
 // local version.
+// TODO switch to updateClusterVersionV3 in 3.6
 func (s *EtcdServer) monitorVersions() {
 	for {
 		select {
@@ -2458,27 +2459,67 @@ func (s *EtcdServer) monitorVersions() {
 			if v != nil {
 				verStr = v.String()
 			}
-			s.GoAttach(func() { s.updateClusterVersion(verStr) })
+			s.GoAttach(func() { s.updateClusterVersionV2(verStr) })
 			continue
 		}
 
 		if v != nil && membership.IsValidVersionChange(s.cluster.Version(), v) {
-			s.GoAttach(func() { s.updateClusterVersion(v.String()) })
+			s.GoAttach(func() { s.updateClusterVersionV2(v.String()) })
 		}
 	}
 }
 
-func (s *EtcdServer) updateClusterVersion(ver string) {
+func (s *EtcdServer) updateClusterVersionV2(ver string) {
 	lg := s.Logger()
 
 	if s.cluster.Version() == nil {
 		lg.Info(
-			"setting up initial cluster version",
+			"setting up initial cluster version using v2 API",
 			zap.String("cluster-version", version.Cluster(ver)),
 		)
 	} else {
 		lg.Info(
-			"updating cluster version",
+			"updating cluster version using v2 API",
+			zap.String("from", version.Cluster(s.cluster.Version().String())),
+			zap.String("to", version.Cluster(ver)),
+		)
+	}
+
+	req := pb.Request{
+		Method: "PUT",
+		Path:   membership.StoreClusterVersionKey(),
+		Val:    ver,
+	}
+
+	ctx, cancel := context.WithTimeout(s.ctx, s.Cfg.ReqTimeout())
+	_, err := s.Do(ctx, req)
+	cancel()
+
+	switch err {
+	case nil:
+		lg.Info("cluster version is updated", zap.String("cluster-version", version.Cluster(ver)))
+		return
+
+	case ErrStopped:
+		lg.Warn("aborting cluster version update; server is stopped", zap.Error(err))
+		return
+
+	default:
+		lg.Warn("failed to update cluster version", zap.Error(err))
+	}
+}
+
+func (s *EtcdServer) updateClusterVersionV3(ver string) {
+	lg := s.Logger()
+
+	if s.cluster.Version() == nil {
+		lg.Info(
+			"setting up initial cluster version using v3 API",
+			zap.String("cluster-version", version.Cluster(ver)),
+		)
+	} else {
+		lg.Info(
+			"updating cluster version using v3 API",
 			zap.String("from", version.Cluster(s.cluster.Version().String())),
 			zap.String("to", version.Cluster(ver)),
 		)

server/etcdserver/server_test.go

@@ -22,6 +22,7 @@ import (
 	"math"
 	"net/http"
 	"os"
+	"path"
 	"path/filepath"
 	"reflect"
 	"sync"
@@ -1716,6 +1717,53 @@ func TestPublishV3Retry(t *testing.T) {
 	<-ch
 }
 
+func TestUpdateVersion(t *testing.T) {
+	n := newNodeRecorder()
+	ch := make(chan interface{}, 1)
+	// simulate that request has gone through consensus
+	ch <- Response{}
+	w := wait.NewWithResponse(ch)
+	ctx, cancel := context.WithCancel(context.TODO())
+	srv := &EtcdServer{
+		lgMu:       new(sync.RWMutex),
+		lg:         zap.NewExample(),
+		id:         1,
+		Cfg:        config.ServerConfig{Logger: zap.NewExample(), TickMs: 1, SnapshotCatchUpEntries: DefaultSnapshotCatchUpEntries},
+		r:          *newRaftNode(raftNodeConfig{lg: zap.NewExample(), Node: n}),
+		attributes: membership.Attributes{Name: "node1", ClientURLs: []string{"http://node1.com"}},
+		cluster:    &membership.RaftCluster{},
+		w:          w,
+		reqIDGen:   idutil.NewGenerator(0, time.Time{}),
+		SyncTicker: &time.Ticker{},
+
+		ctx:    ctx,
+		cancel: cancel,
+	}
+	srv.updateClusterVersionV2("2.0.0")
+
+	action := n.Action()
+	if len(action) != 1 {
+		t.Fatalf("len(action) = %d, want 1", len(action))
+	}
+	if action[0].Name != "Propose" {
+		t.Fatalf("action = %s, want Propose", action[0].Name)
+	}
+	data := action[0].Params[0].([]byte)
+	var r pb.Request
+	if err := r.Unmarshal(data); err != nil {
+		t.Fatalf("unmarshal request error: %v", err)
+	}
+	if r.Method != "PUT" {
+		t.Errorf("method = %s, want PUT", r.Method)
+	}
+	if wpath := path.Join(StoreClusterPrefix, "version"); r.Path != wpath {
+		t.Errorf("path = %s, want %s", r.Path, wpath)
+	}
+	if r.Val != "2.0.0" {
+		t.Errorf("val = %s, want %s", r.Val, "2.0.0")
+	}
+}
+
 func TestStopNotify(t *testing.T) {
 	s := &EtcdServer{
 		lgMu: new(sync.RWMutex),