feat(go): track gateway active connections

go/vehicle-gateway/internal/gateway/tcp_server.go

@@ -145,6 +145,8 @@ func (s *TCPServer) handleConnection(ctx context.Context, conn net.Conn) {
 	defer conn.Close()
 	source := conn.RemoteAddr().String()
 	log := s.logger.With("protocol", s.protocol.Protocol, "remote", source)
+	s.recordConnectionMetric(1)
+	defer s.recordConnectionMetric(-1)
 	log.Info("tcp connection opened")
 	defer log.Info("tcp connection closed")
 
@@ -268,6 +270,15 @@ func (s *TCPServer) recordPublishMetric(kind string, status string) {
 	})
 }
 
+func (s *TCPServer) recordConnectionMetric(delta float64) {
+	if s.metrics == nil {
+		return
+	}
+	s.metrics.AddGauge("vehicle_gateway_active_connections", metrics.Labels{
+		"protocol": string(s.protocol.Protocol),
+	}, delta)
+}
+
 func (p TCPProtocol) String() string {
 	return fmt.Sprintf("%s@%s", p.Protocol, p.Addr)
 }