feat(go): expose bridge batch pressure metrics

go/vehicle-gateway/cmd/nats-kafka-bridge/main.go

@@ -240,20 +240,29 @@ func bridgeBatch(ctx context.Context, registry *metrics.Registry, writer kafkaBa
 	if len(messages) == 0 {
 		return nil
 	}
+	started := time.Now()
+	status := "ok"
+	defer func() {
+		recordBridgeBatchDuration(registry, status, time.Since(started))
+		recordBridgeBatchPending(registry, 0, 0)
+	}()
 	kafkaMessages := make([]kafka.Message, 0, len(messages))
 	for _, message := range messages {
 		addBridgeSubjectMetric(registry, "vehicle_bridge_messages_total", message.subject, "received")
 		topic, ok := route[message.subject]
 		if !ok || topic == "" {
 			addBridgeSubjectMetric(registry, "vehicle_bridge_messages_total", message.subject, "route_error")
+			status = "error"
 			return fmt.Errorf("kafka topic not configured for nats subject %q", message.subject)
 		}
 		kafkaMessages = append(kafkaMessages, kafkaMessage(topic, message.data))
 	}
+	recordBridgeBatchPending(registry, len(messages), len(kafkaMessages))
 	if err := writer.WriteMessages(ctx, kafkaMessages...); err != nil {
 		for _, message := range kafkaMessages {
 			addBridgeTopicMetric(registry, "vehicle_bridge_kafka_writes_total", message.Topic, "error")
 		}
+		status = "error"
 		return err
 	}
 	for _, message := range kafkaMessages {
@@ -265,6 +274,7 @@ func bridgeBatch(ctx context.Context, registry *metrics.Registry, writer kafkaBa
 		}
 		if err := message.ack(); err != nil {
 			addBridgeSubjectMetric(registry, "vehicle_bridge_nats_acks_total", message.subject, "error")
+			status = "error"
 			return err
 		}
 		addBridgeSubjectMetric(registry, "vehicle_bridge_nats_acks_total", message.subject, "ok")
@@ -272,6 +282,8 @@ func bridgeBatch(ctx context.Context, registry *metrics.Registry, writer kafkaBa
 	return nil
 }
 
+var bridgeBatchDurationBucketsMS = []float64{1, 5, 10, 25, 50, 100, 250, 500, 1000, 5000}
+
 func addBridgeSubjectMetric(registry *metrics.Registry, name string, subject string, status string) {
 	if registry == nil {
 		return
@@ -286,6 +298,23 @@ func addBridgeTopicMetric(registry *metrics.Registry, name string, topic string,
 	registry.IncCounter(name, metrics.Labels{"topic": topic, "status": status})
 }
 
+func recordBridgeBatchPending(registry *metrics.Registry, messages int, kafkaMessages int) {
+	if registry == nil {
+		return
+	}
+	registry.SetGauge("vehicle_bridge_batch_pending_messages", nil, float64(messages))
+	registry.SetGauge("vehicle_bridge_batch_pending_kafka_messages", nil, float64(kafkaMessages))
+}
+
+func recordBridgeBatchDuration(registry *metrics.Registry, status string, elapsed time.Duration) {
+	if registry == nil {
+		return
+	}
+	registry.ObserveHistogram("vehicle_bridge_batch_duration_ms_histogram", metrics.Labels{
+		"status": status,
+	}, bridgeBatchDurationBucketsMS, float64(elapsed.Milliseconds()))
+}
+
 func recordNATSConsumerInfoMetrics(registry *metrics.Registry, cfg config, info *nats.ConsumerInfo) {
 	if registry == nil || info == nil {
 		return

go/vehicle-gateway/cmd/nats-kafka-bridge/main_test.go

@@ -91,6 +91,49 @@ func TestBridgeBatchRecordsMetrics(t *testing.T) {
 	}
 }
 
+func TestBridgeBatchExposesPendingAndDurationMetrics(t *testing.T) {
+	env := envelope.FrameEnvelope{Protocol: envelope.ProtocolGB32960, VIN: "VIN001", MessageID: "0x02"}
+	payload, err := json.Marshal(env)
+	if err != nil {
+		t.Fatal(err)
+	}
+	registry := metrics.NewRegistry()
+	writer := &recordingBridgeWriter{
+		onWrite: func() {
+			text := registry.Render()
+			for _, want := range []string{
+				`vehicle_bridge_batch_pending_messages 2`,
+				`vehicle_bridge_batch_pending_kafka_messages 2`,
+			} {
+				if !strings.Contains(text, want) {
+					t.Fatalf("pending bridge metric missing %s during write:\n%s", want, text)
+				}
+			}
+		},
+	}
+
+	err = bridgeBatch(context.Background(), registry, writer, []bridgeMessage{
+		{subject: "vehicle.raw.go.gb32960.v1", data: payload, ack: func() error { return nil }},
+		{subject: "vehicle.raw.go.gb32960.v1", data: payload, ack: func() error { return nil }},
+	}, map[string]string{"vehicle.raw.go.gb32960.v1": "vehicle.raw.go.gb32960.v1"})
+	if err != nil {
+		t.Fatalf("bridgeBatch() error = %v", err)
+	}
+
+	text := registry.Render()
+	for _, want := range []string{
+		`vehicle_bridge_batch_pending_messages 0`,
+		`vehicle_bridge_batch_pending_kafka_messages 0`,
+		`vehicle_bridge_batch_duration_ms_histogram_bucket{le="+Inf",status="ok"} 1`,
+		`vehicle_bridge_batch_duration_ms_histogram_count{status="ok"} 1`,
+		`vehicle_bridge_batch_duration_ms_histogram_sum{status="ok"}`,
+	} {
+		if !strings.Contains(text, want) {
+			t.Fatalf("bridge batch metric missing %s:\n%s", want, text)
+		}
+	}
+}
+
 func TestRecordNATSConsumerInfoMetrics(t *testing.T) {
 	registry := metrics.NewRegistry()
 	cfg := config{NATSStream: "VEHICLE_INGEST", NATSDurable: "vehicle-kafka-bridge"}
@@ -148,9 +191,13 @@ func TestLoadConfigIncludesUnifiedOnlyWhenExplicitlyConfigured(t *testing.T) {
 type recordingBridgeWriter struct {
 	messages []kafka.Message
 	err      error
+	onWrite  func()
 }
 
 func (w *recordingBridgeWriter) WriteMessages(_ context.Context, messages ...kafka.Message) error {
+	if w.onWrite != nil {
+		w.onWrite()
+	}
 	if w.err != nil {
 		return w.err
 	}