package metrics

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/expvar"

func main() {
	myCount := expvar.NewCounter("my_count")
	myCount.Add(1)
}

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

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

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

var requestDuration = prometheus.NewSummary(stdprometheus.SummaryOpts{
	Namespace: "myservice",
	Subsystem: "api",
	Name:      "request_duration_nanoseconds_count",
	Help:      "Total time spent serving requests.",
}, []string{})

func handleRequest() {
	defer func(begin time.Time) { requestDuration.Observe(time.Since(begin)) }(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/statsd"
)

func main() {
	statsdWriter, err := net.Dial("udp", "127.0.0.1:8126")
	if err != nil {
		panic(err)
	}

	reportInterval := 5 * time.Second
	goroutines := statsd.NewGauge(statsdWriter, "total_goroutines", reportInterval)
	for range time.Tick(reportInterval) {
		goroutines.Set(float64(runtime.NumGoroutine()))
	}
}