commit transaction for each configuration change

Current when etcd remove a member, it just removes it from bbolt db,
but doesn't update the cache. On the other hands, etcd periodically
commit each bbolt transaction. When etcd processes the next conf
change request, it might not have commit the previous member remove
request into bbolt. Accordingly it breaks the linerizability.

Signed-off-by: Benjamin Wang <benjamin.ahrtr@gmail.com>

server/etcdserver/server.go

@@ -1809,6 +1809,11 @@ func (s *EtcdServer) apply(
 			var cc raftpb.ConfChange
 			pbutil.MustUnmarshal(&cc, e.Data)
 			removedSelf, err := s.applyConfChange(cc, confState, shouldApplyV3)
+			if err != nil {
+				s.lg.Error("failed to apply conf change", zap.Bool("shouldApplyV3", bool(shouldApplyV3)), zap.Error(err))
+			} else {
+				s.KV().Commit()
+			}
 			s.setAppliedIndex(e.Index)
 			s.setTerm(e.Term)
 			shouldStop = shouldStop || removedSelf

tests/e2e/ctl_v3_member_no_proxy_test.go

@@ -40,28 +40,27 @@ func TestMemberReplace(t *testing.T) {
 	require.NoError(t, err)
 	defer epc.Close()
 
-	memberId := rand.Int() % len(epc.Procs)
-	member := epc.Procs[memberId]
+	memberIdx := rand.Int() % len(epc.Procs)
+	member := epc.Procs[memberIdx]
 	memberName := member.Config().Name
 	var endpoints []string
 	for i := 1; i < len(epc.Procs); i++ {
-		endpoints = append(endpoints, epc.Procs[(memberId+i)%len(epc.Procs)].EndpointsGRPC()...)
+		endpoints = append(endpoints, epc.Procs[(memberIdx+i)%len(epc.Procs)].EndpointsGRPC()...)
 	}
 	cc, err := e2e.NewEtcdctl(epc.Cfg.Client, endpoints)
 	require.NoError(t, err)
 
-	c := epc.Etcdctl()
-	memberID, found, err := getMemberIdByName(ctx, c, memberName)
+	memberID, found, err := getMemberIdByName(ctx, cc, memberName)
 	require.NoError(t, err)
 	require.Equal(t, found, true, "Member not found")
 
 	// Need to wait health interval for cluster to accept member changes
 	time.Sleep(etcdserver.HealthInterval)
 
 	t.Logf("Removing member %s", memberName)
-	_, err = c.MemberRemove(ctx, memberID)
+	_, err = cc.MemberRemove(ctx, memberID)
 	require.NoError(t, err)
-	_, found, err = getMemberIdByName(ctx, c, memberName)
+	_, found, err = getMemberIdByName(ctx, cc, memberName)
 	require.NoError(t, err)
 	require.Equal(t, found, false, "Expected member to be removed")
 	for member.IsRunning() {
@@ -82,12 +81,14 @@ func TestMemberReplace(t *testing.T) {
 	err = patchArgs(member.Config().Args, "initial-cluster-state", "existing")
 	require.NoError(t, err)
 
+	// Sleep 100ms to bypass the known issue https://github.com/etcd-io/etcd/issues/16687.
+	time.Sleep(100 * time.Millisecond)
 	t.Logf("Starting member %s", memberName)
 	err = member.Start(ctx)
 	require.NoError(t, err)
 	testutils.ExecuteUntil(ctx, t, func() {
 		for {
-			_, found, err := getMemberIdByName(ctx, c, memberName)
+			_, found, err := getMemberIdByName(ctx, cc, memberName)
 			if err != nil || !found {
 				time.Sleep(10 * time.Millisecond)
 				continue