Metrics

Arrower uses OpenTelemetry for metrics with a Prometheus exporter. The MeterProvider is part of the DI container and configured out of the box. Use any OTEL-compatible backend - Prometheus + Grafana are shipped in the Docker Compose for convenience.

What Gets Measured Automatically

Component	Metrics
HTTP requests	Request count, duration, errors (via otelecho middleware)
Use cases	Invocation counter, duration histogram per use case type
Jobs	Processed count, duration per queue and job type
Renderer	Template render count and duration

No setup required. These metrics are collected as long as the DI container initialises the providers.

Custom Metrics

Access the MeterProvider from the container and create your own instruments:

meter := di.MeterProvider.Meter("myapp")

counter, _ := meter.Int64Counter("orders_created",
    metric.WithDescription("Total orders created"),
)

counter.Add(ctx, 1, metric.WithAttributes(
    attribute.String("region", "eu-west"),
))

Endpoint

Metrics are served on a separate port from your application, so the endpoint can be protected from public access and only reachable by your infrastructure.

Configuration:

http:
  status_endpoint_enabled: true
  status_endpoint_port: 2223

Path	Description
:2223/metrics	Prometheus scrape endpoint
:2223/status	Application health and system status

Disable with status_endpoint_enabled: false.

Viewing Metrics

For local development, the Docker Compose ships Grafana and Prometheus pre-configured. Point your browser at Grafana and the Arrower dashboard is ready.

In production, point your Prometheus instance at the metrics endpoint. Any OTEL-compatible backend works - you are not tied to Grafana or Prometheus.

Use Case Decorators

To add metrics to your own use cases, wrap them with the provided decorators:

// Individual decorators
handler := app.NewMeteredRequest(di.MeterProvider, NewMyHandler())

// Or apply tracing + metrics + logging at once
handler := app.NewInstrumentedRequest(
    di.TraceProvider, di.MeterProvider, di.Logger,
    NewMyHandler(),
)

See Use Cases - Instrumentation for all available decorators.