1# package metrics
2
3`package metrics` provides a set of uniform interfaces for service instrumentation.
4It has
5 [counters](http://prometheus.io/docs/concepts/metric_types/#counter),
6 [gauges](http://prometheus.io/docs/concepts/metric_types/#gauge), and
7 [histograms](http://prometheus.io/docs/concepts/metric_types/#histogram),
8and provides adapters to popular metrics packages, like
9 [expvar](https://golang.org/pkg/expvar),
10 [StatsD](https://github.com/etsy/statsd), and
11 [Prometheus](https://prometheus.io).
12
13## Rationale
14
15Code instrumentation is absolutely essential to achieve
16 [observability](https://speakerdeck.com/mattheath/observability-in-micro-service-architectures)
17 into a distributed system.
18Metrics and instrumentation tools have coalesced around a few well-defined idioms.
19`package metrics` provides a common, minimal interface those idioms for service authors.
20
21## Usage
22
23A simple counter, exported via expvar.
24
25```go
26import (
27 "github.com/go-kit/kit/metrics"
28 "github.com/go-kit/kit/metrics/expvar"
29)
30
31func main() {
32 var myCount metrics.Counter
33 myCount = expvar.NewCounter("my_count")
34 myCount.Add(1)
35}
36```
37
38A histogram for request duration,
39 exported via a Prometheus summary with dynamically-computed quantiles.
40
41```go
42import (
43 "time"
44
45 stdprometheus "github.com/prometheus/client_golang/prometheus"
46
47 "github.com/go-kit/kit/metrics"
48 "github.com/go-kit/kit/metrics/prometheus"
49)
50
51func main() {
52 var dur metrics.Histogram = prometheus.NewSummaryFrom(stdprometheus.SummaryOpts{
53 Namespace: "myservice",
54 Subsystem: "api",
55 Name: "request_duration_seconds",
56 Help: "Total time spent serving requests.",
57 }, []string{})
58 // ...
59}
60
61func handleRequest(dur metrics.Histogram) {
62 defer func(begin time.Time) { dur.Observe(time.Since(begin).Seconds()) }(time.Now())
63 // handle request
64}
65```
66
67A gauge for the number of goroutines currently running, exported via StatsD.
68
69```go
70import (
71 "context"
72 "net"
73 "os"
74 "runtime"
75 "time"
76
77 "github.com/go-kit/kit/metrics"
78 "github.com/go-kit/kit/metrics/statsd"
79)
80
81func main() {
82 statsd := statsd.New("foo_svc.", log.NewNopLogger())
83 report := time.NewTicker(5 * time.Second)
84 defer report.Stop()
85 go statsd.SendLoop(context.Background(), report.C, "tcp", "statsd.internal:8125")
86 goroutines := statsd.NewGauge("goroutine_count")
87 go exportGoroutines(goroutines)
88 // ...
89}
90
91func exportGoroutines(g metrics.Gauge) {
92 for range time.Tick(time.Second) {
93 g.Set(float64(runtime.NumGoroutine()))
94 }
95}
96```
97
98For more information, see [the package documentation](https://godoc.org/github.com/go-kit/kit/metrics).
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