embed: gracefully shut down gRPC server

Fix #7322.

Signed-off-by: Gyu-Ho Lee <gyuhox@gmail.com>

embed/etcd.go

@@ -148,6 +148,14 @@ func (e *Etcd) Config() Config {
 func (e *Etcd) Close() {
 	e.closeOnce.Do(func() { close(e.stopc) })
 
+	// (gRPC server) stops accepting new connections,
+	// RPCs, and blocks until all pending RPCs are finished
+	for _, sctx := range e.sctxs {
+		for gs := range sctx.grpcServerC {
+			gs.GracefulStop()
+		}
+	}
+
 	for _, sctx := range e.sctxs {
 		sctx.cancel()
 	}

embed/serve.go

@@ -52,11 +52,14 @@ type serveCtx struct {
 
 	userHandlers    map[string]http.Handler
 	serviceRegister func(*grpc.Server)
+	grpcServerC     chan *grpc.Server
 }
 
 func newServeCtx() *serveCtx {
 	ctx, cancel := context.WithCancel(context.Background())
-	return &serveCtx{ctx: ctx, cancel: cancel, userHandlers: make(map[string]http.Handler)}
+	return &serveCtx{ctx: ctx, cancel: cancel, userHandlers: make(map[string]http.Handler),
+		grpcServerC: make(chan *grpc.Server, 2), // in case sctx.insecure,sctx.secure true
+	}
 }
 
 // serve accepts incoming connections on the listener l,
@@ -72,8 +75,11 @@ func (sctx *serveCtx) serve(s *etcdserver.EtcdServer, tlscfg *tls.Config, handle
 	servElection := v3election.NewElectionServer(v3c)
 	servLock := v3lock.NewLockServer(v3c)
 
+	defer close(sctx.grpcServerC)
+
 	if sctx.insecure {
 		gs := v3rpc.Server(s, nil)
+		sctx.grpcServerC <- gs
 		v3electionpb.RegisterElectionServer(gs, servElection)
 		v3lockpb.RegisterLockServer(gs, servLock)
 		if sctx.serviceRegister != nil {
@@ -103,6 +109,7 @@ func (sctx *serveCtx) serve(s *etcdserver.EtcdServer, tlscfg *tls.Config, handle
 
 	if sctx.secure {
 		gs := v3rpc.Server(s, tlscfg)
+		sctx.grpcServerC <- gs
 		v3electionpb.RegisterElectionServer(gs, servElection)
 		v3lockpb.RegisterLockServer(gs, servLock)
 		if sctx.serviceRegister != nil {