Metrics

Copper’s cmetrics package provides Prometheus metrics with a declare-then-use model: register your counters and histograms up front, then emit them from anywhere. The cprometheus package (from gocopper/pkg) exposes them over HTTP.

Declaring Metrics

To declare your application’s metrics, provide a *cmetrics.Registry and add cmetrics.WireModule to your wire set:

pkg/app/metrics.go

func MetricsRegistry() *cmetrics.Registry {
	return cmetrics.NewRegistry(cmetrics.NewRegistryParams{
		Counters: []cmetrics.Counter{
			{Name: "rocket_launches_total", Labels: []string{"status"}},
		},
		Histograms: []cmetrics.Histogram{
			{Name: "launch_duration_seconds", Labels: []string{"rocket"}, Buckets: []float64{1, 5, 15, 60}},
		},
	})
}

Projects scaffolded with copper create already include this file and the wiring, so you only need to add your metrics to the registry.

Emitting Metrics

To emit a metric, inject cmetrics.Metrics and reference the metric by name:

s.metrics.CounterInc("rocket_launches_total", map[string]string{"status": "success"})

s.metrics.HistogramObserve("launch_duration_seconds", map[string]string{"rocket": rocket.Name}, dur.Seconds())

Emitting an unregistered metric name (or a mismatched label set) logs a warning and does nothing; it will never panic or return an error.

Built-in HTTP Metrics

Every registry automatically includes two built-in metrics, which are emitted by chttp.RequestLoggerMiddleware (wired in by default):

http_requests_total{status_code, path}
http_request_duration_seconds{status_code, path}

The path label is the route template (/api/rockets/{id}) rather than the raw URL, so cardinality stays manageable.

Exposing the Metrics Endpoint

To expose your metrics over HTTP, add cprometheus.WireModule, register *cprometheus.Router in your handler, and enable the endpoint in your config:

[cprometheus]
http_enabled = true
http_path = "/internal/metrics" # default

The endpoint is disabled by default, so you may enable it only in the environments that Prometheus scrapes.

Getting Started

The Basics

Architecture

HTTP

Database

Frontend

Digging Deeper

Reference

Declaring Metrics

Emitting Metrics

Built-in HTTP Metrics

Exposing the Metrics Endpoint

​Declaring Metrics

​Emitting Metrics

​Built-in HTTP Metrics

​Exposing the Metrics Endpoint

Declaring Metrics

Emitting Metrics

Built-in HTTP Metrics

Exposing the Metrics Endpoint