etcdserver: add 'OnShutdown', stop gRPC server

Fix #7322.

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

etcdserver/config.go

@@ -61,6 +61,12 @@ type ServerConfig struct {
 	ClientCertAuthEnabled bool
 
 	AuthToken string
+
+	// OnShutdown gracefully stops gRPC server on shutdown.
+	// It first stops accepting new connections, RPCs, and
+	// blocks until all pending RPCs are finished
+	// TODO: drain other requests
+	OnShutdown func()
 }
 
 // VerifyBootstrap sanity-checks the initial config for bootstrap case

etcdserver/server.go

@@ -689,6 +689,12 @@ func (s *EtcdServer) run() {
 	}
 
 	defer func() {
+		// stop accepting new connections, RPCs,
+		// and blocks until all pending RPCs are finished
+		if s.Cfg.OnShutdown != nil {
+			s.Cfg.OnShutdown()
+		}
+
 		s.wgMu.Lock() // block concurrent waitgroup adds in goAttach while stopping
 		close(s.stopping)
 		s.wgMu.Unlock()