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