etcdserver: add 'OnShutdown', stop gRPC server

Fix etcd-io#7322.

Signed-off-by: Gyu-Ho Lee <[email protected]>

etcdserver/config.go

@@ -61,6 +61,9 @@ type ServerConfig struct {
 	ClientCertAuthEnabled bool
 
 	AuthToken string
+
+	// OnShutdown is called immediately before releasing etcd server resources.
+	OnShutdown func()
 }
 
 // VerifyBootstrap sanity-checks the initial config for bootstrap case

etcdserver/server.go

@@ -689,6 +689,13 @@ func (s *EtcdServer) run() {
 	}
 
 	defer func() {
+		if s.Cfg != nil && s.Cfg.OnShutdown != nil {
+			// gRPC server stops accepting new connections,
+			// RPCs, and blocks until all pending RPCs are finished
+			// TODO: drain other pending requests?
+			s.Cfg.OnShutdown()
+		}
+
 		s.wgMu.Lock() // block concurrent waitgroup adds in goAttach while stopping
 		close(s.stopping)
 		s.wgMu.Unlock()