# 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][]**.
[counters]: http://prometheus.io/docs/concepts/metric_types/#counter
[gauges]: http://prometheus.io/docs/concepts/metric_types/#gauge
[histograms]: http://prometheus.io/docs/concepts/metric_types/#histogram
[expvar]: https://golang.org/pkg/expvar
[statsd]: https://github.com/etsy/statsd
[Prometheus]: http://prometheus.io
## Rationale
TODO
## Usage
A simple counter, exported via expvar.
```go
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.
```go
import (
stdprometheus "github.com/prometheus/client_golang/prometheus"
"github.com/go-kit/kit/metrics"
"github.com/go-kit/kit/metrics/prometheus"
"github.com/go-kit/kit/metrics/statsd"
)
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
}
```