Add prometheus metrics modules

metrics/metrics.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"net/http"
 	"strconv"
+	"sync"
 	"time"
 	"unicode/utf8"
 
@@ -19,37 +20,26 @@ type Prometheus struct {
 	ReqCntURLLabelMappingFn func(c *gin.Context) string
 	SkipMetricsURLFn        func(c *gin.Context) bool
 	reg                     *prometheus.Registry
+	init                    sync.Once
+	cs                      []prometheus.Collector
 }
 
-func initRegistry(cs ...prometheus.Collector) *Prometheus {
-	reg := prometheus.NewPedanticRegistry()
-	reg.MustRegister(
-		collectors.NewProcessCollector(collectors.ProcessCollectorOpts{}),
-		collectors.NewGoCollector(),
-	)
-	p := &Prometheus{
-		reqCnt: reqCnt,
-		reqDur: reqDur,
-		ReqCntURLLabelMappingFn: func(c *gin.Context) string {
-			return c.Request.URL.Path
-		},
-		SkipMetricsURLFn: func(c *gin.Context) bool {
-			return false
-		},
-		reg: reg,
-	}
-	reg.MustRegister(p.reqCnt)
-	reg.MustRegister(p.reqDur)
-	for _, c := range cs {
-		reg.MustRegister(c)
-	}
-	return p
+// New creates Prometheus instance with given collectors.
+// Before usage p.Init() must be called.
+func New(cs ...prometheus.Collector) *Prometheus {
+	return &Prometheus{cs: cs}
 }
 
+// NewPrometheus creates registers collectors and starts metrics server.
+// Deprecated: This function will panic instead of returning error. Use metrics module instead.
 func NewPrometheus(port int, cs ...prometheus.Collector) *Prometheus {
+	p := New(cs...)
+	if err := p.Init(); err != nil {
+		panic(err)
+	}
+
 	pMux := http.NewServeMux()
-	p := initRegistry(cs...)
-	pMux.Handle("/metrics", promhttp.HandlerFor(p.reg, promhttp.HandlerOpts{}))
+	pMux.Handle("/metrics", NewPrometheusHandler(p))
 	go func() {
 		listenAddr := fmt.Sprintf(":%d", port)
 
@@ -66,6 +56,32 @@ func NewPrometheus(port int, cs ...prometheus.Collector) *Prometheus {
 	return p
 }
 
+func (p *Prometheus) Init() (err error) {
+	p.init.Do(func() {
+		p.reqCnt = reqCnt
+		p.reqDur = reqDur
+		p.ReqCntURLLabelMappingFn = func(c *gin.Context) string { return c.Request.URL.Path }
+		p.SkipMetricsURLFn = func(c *gin.Context) bool { return false }
+		p.reg = prometheus.NewPedanticRegistry()
+
+		collectors := []prometheus.Collector{
+			collectors.NewProcessCollector(collectors.ProcessCollectorOpts{}),
+			collectors.NewGoCollector(),
+			p.reqCnt,
+			p.reqDur,
+		}
+
+		collectors = append(collectors, p.cs...)
+		for _, c := range collectors {
+			if err = p.reg.Register(c); err != nil {
+				return
+			}
+		}
+	})
+
+	return err
+}
+
 func (p *Prometheus) GetRegistry() *prometheus.Registry {
 	return p.reg
 }
@@ -93,3 +109,8 @@ func (p *Prometheus) HandlerFunc() gin.HandlerFunc {
 		}
 	}
 }
+
+// NewPrometheusHandler creates http.Handler with Prometheus registry.
+func NewPrometheusHandler(p *Prometheus) http.Handler {
+	return promhttp.HandlerFor(p.reg, promhttp.HandlerOpts{})
+}

service/module/httpserver/pprof/pprof_test.go

@@ -22,10 +22,11 @@ func TestServer(t *testing.T) {
 
 	require.NotEmpty(t, srv.Name())
 	require.NoError(t, srv.Init())
+	url := srv.URL() + "/debug/pprof/heap"
 	wg := &multierror.Group{}
 	wg.Go(srv.Run)
 
-	assertOK(t, srv.URL()+"/debug/pprof/heap")
+	assertOK(t, url)
 
 	assert.NoError(t, srv.Stop())
 	err := wg.Wait().ErrorOrNil()

service/module/httpserver/prom/prom.go

@@ -0,0 +1,21 @@
+// Package prom provides prometheus metrics handler options for httpserver module.
+package prom
+
+import (
+	"fmt"
+
+	"github.com/elisasre/go-common/metrics"
+	"github.com/elisasre/go-common/service/module/httpserver"
+)
+
+// WithMetrics replaces servers handler with http.Handler which is instrumented with /metrics endpoint.
+// This option is meant be used with stand alone metrics server, not embedded inside application server.
+// For serving metrics endpoint inside your application web server check lower level functionalities from metrics.
+func WithMetrics(p *metrics.Prometheus) httpserver.Opt {
+	return func(s *httpserver.Server) error {
+		if err := p.Init(); err != nil {
+			return fmt.Errorf("failed to initialize prometheus handler: %w", err)
+		}
+		return httpserver.WithHandler(metrics.NewPrometheusHandler(p))(s)
+	}
+}

service/module/httpserver/prom/prom_test.go

@@ -0,0 +1,64 @@
+package prom_test
+
+import (
+	"io"
+	"net/http"
+	"testing"
+	"time"
+
+	"github.com/elisasre/go-common/metrics"
+	"github.com/elisasre/go-common/service/module/httpserver"
+	"github.com/elisasre/go-common/service/module/httpserver/prom"
+	"github.com/hashicorp/go-multierror"
+	"github.com/prometheus/client_golang/prometheus/collectors"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestInitError(t *testing.T) {
+	c := collectors.NewGoCollector()
+	srv := httpserver.New(
+		httpserver.WithServer(&http.Server{ReadHeaderTimeout: time.Second}),
+		httpserver.WithAddr("127.0.0.1:0"),
+		prom.WithMetrics(metrics.New(c)),
+	)
+
+	require.Error(t, srv.Init())
+}
+
+func TestServer(t *testing.T) {
+	srv := httpserver.New(
+		httpserver.WithServer(&http.Server{ReadHeaderTimeout: time.Second}),
+		httpserver.WithAddr("127.0.0.1:0"),
+		prom.WithMetrics(metrics.New()),
+	)
+
+	require.NotEmpty(t, srv.Name())
+	require.NoError(t, srv.Init())
+	url := srv.URL() + "/metrics"
+	wg := &multierror.Group{}
+	wg.Go(srv.Run)
+
+	assertOK(t, url)
+
+	assert.NoError(t, srv.Stop())
+	err := wg.Wait().ErrorOrNil()
+	require.NoError(t, err)
+}
+
+func assertOK(t testing.TB, url string) {
+	resp, err := http.Get(url) //nolint:gosec
+	if !assert.NoError(t, err) {
+		return
+	}
+
+	data, err := io.ReadAll(resp.Body)
+	if !assert.NoError(t, err) {
+		return
+	}
+
+	assert.Equal(t, "200 OK", resp.Status)
+	assert.Equal(t, http.StatusOK, resp.StatusCode)
+	assert.NoError(t, resp.Body.Close())
+	assert.NotEmpty(t, data)
+}