add grpc keep-alive support

server/hdl_grpc.go

@@ -121,6 +121,22 @@ func serveGrpc(addr string, tlsConf *tls.Config) (*grpc.Server, error) {
 		opts = append(opts, grpc.Creds(credentials.NewTLS(tlsConf)))
 		secure = " secure"
 	}
+
+	kepConfig := keepalive.EnforcementPolicy{
+		MinTime:             1 * time.Second, // If a client pings more than once every second, terminate the connection
+		PermitWithoutStream: true,            // Allow pings even when there are no active streams
+	}
+
+	kpConfig := keepalive.ServerParameters{
+		MaxConnectionIdle:     15 * time.Second, // If a client is idle for 15 seconds, send a GOAWAY
+		MaxConnectionAge:      30 * time.Second, // If any connection is alive for more than 30 seconds, send a GOAWAY
+		MaxConnectionAgeGrace: 5 * time.Second,  // Allow 5 seconds for pending RPCs to complete before forcibly closing connections
+		Time:                  5 * time.Second,  // Ping the client if it is idle for 5 seconds to ensure the connection is still active
+		Timeout:               1 * time.Second,  // Wait 1 second for the ping ack before assuming the connection is dead
+	}
+	opts = append(opts, grpc.KeepaliveEnforcementPolicy(kepConfig))
+	opts = append(opts, grpc.KeepaliveParams(kpConfig))
+
 	srv := grpc.NewServer(opts...)
 	pbx.RegisterNodeServer(srv, &grpcNodeServer{})
 	log.Printf("gRPC/%s%s server is registered at [%s]", grpc.Version, secure, addr)