package metrics provides a set of uniform interfaces for service instrumentation. It has counters, gauges, and histograms, and provides adapters to popular metrics packages, like expvar, StatsD, and Prometheus.

Rationale

Code instrumentation is absolutely essential to achieve observability into a distributed system. Metrics and instrumentation tools have coalesced around a few well-defined idioms. package metrics provides a common, minimal interface those idioms for service authors.

Usage

A simple counter, exported via expvar.

import (
	"github.com/go-kit/kit/metrics"
	"github.com/go-kit/kit/metrics/expvar"
)

func main() {
	var myCount metrics.Counter
	myCount = expvar.NewCounter("my_count")
	myCount.Add(1)
}

A histogram for request duration, exported via a Prometheus summary with dynamically-computed quantiles.

import (
	"time"

	stdprometheus "github.com/prometheus/client_golang/prometheus"

	"github.com/go-kit/kit/metrics"
	"github.com/go-kit/kit/metrics/prometheus"
)

func main() {
	var dur metrics.Histogram = prometheus.NewSummary(stdprometheus.SummaryOpts{
		Namespace: "myservice",
		Subsystem: "api",
		Name:     "request_duration_seconds",
		Help:     "Total time spent serving requests.",
	}, []string{})
	// ...
}

func handleRequest(dur metrics.Histogram) {
	defer func(begin time.Time) { dur.Observe(time.Since(begin).Seconds()) }(time.Now())
	// handle request
}

A gauge for the number of goroutines currently running, exported via StatsD.

import (
	"net"
	"os"
	"runtime"
	"time"

	"github.com/go-kit/kit/metrics"
	"github.com/go-kit/kit/metrics/statsd"
)

func main() {
	statsd := statsd.New("foo_svc.", log.NewNopLogger())
	report := time.NewTicker(5 * time.Second)
	defer report.Stop()
	go statsd.SendLoop(report.C, "tcp", "statsd.internal:8125")
	goroutines := statsd.NewGauge("goroutine_count")
	go exportGoroutines(goroutines)
	// ...
}

func exportGoroutines(g metrics.Gauge) {
	for range time.Tick(time.Second) {
		g.Set(float64(runtime.NumGoroutine()))
	}
}