add prometheus metrics endpoint

cmd/task/main.go

@@ -3,12 +3,14 @@ package main
 import (
 	"context"
 	"errors"
+	"fmt"
 	"log"
 	"net"
 	"net/http"
 	"time"
 
 	"github.com/kelseyhightower/envconfig"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 	"go.mongodb.org/mongo-driver/mongo"
 	"go.mongodb.org/mongo-driver/mongo/options"
 	"go.uber.org/zap"
@@ -162,6 +164,9 @@ func main() {
 	goahealthsrv.Mount(mux, healthServer)
 	goaopenapisrv.Mount(mux, openapiServer)
 
+	// expose metrics
+	go exposeMetrics(cfg.Metrics.Addr, logger)
+
 	var handler http.Handler = mux
 	srv := &http.Server{
 		Addr:         cfg.HTTP.Host + ":" + cfg.HTTP.Port,
@@ -228,3 +233,12 @@ func httpClient() *http.Client {
 		Timeout: 30 * time.Second,
 	}
 }
+
+func exposeMetrics(addr string, logger *zap.Logger) {
+	promMux := http.NewServeMux()
+	promMux.Handle("/metrics", promhttp.Handler())
+	logger.Info(fmt.Sprintf("exposing prometheus metrics at %s/metrics", addr))
+	if err := http.ListenAndServe(addr, promMux); err != nil {
+		logger.Error("error exposing prometheus metrics", zap.Error(err))
+	}
+}

go.mod

@@ -7,6 +7,7 @@ require (
 	github.com/cenkalti/backoff/v4 v4.1.3
 	github.com/google/uuid v1.3.0
 	github.com/kelseyhightower/envconfig v1.4.0
+	github.com/prometheus/client_golang v1.12.2
 	github.com/stretchr/testify v1.7.0
 	go.mongodb.org/mongo-driver v1.8.4
 	go.uber.org/zap v1.21.0
@@ -15,10 +16,13 @@ require (
 )
 
 require (
+	github.com/beorn7/perks v1.0.1 // indirect
+	github.com/cespare/xxhash/v2 v2.1.2 // indirect
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/dimfeld/httppath v0.0.0-20170720192232-ee938bf73598 // indirect
 	github.com/dimfeld/httptreemux/v5 v5.4.0 // indirect
 	github.com/go-stack/stack v1.8.0 // indirect
+	github.com/golang/protobuf v1.5.2 // indirect
 	github.com/golang/snappy v0.0.1 // indirect
 	github.com/google/go-cmp v0.5.6 // indirect
 	github.com/gopherjs/gopherjs v0.0.0-20220221023154-0b2280d3ff96 // indirect
@@ -26,8 +30,12 @@ require (
 	github.com/jtolds/gls v4.20.0+incompatible // indirect
 	github.com/klauspost/compress v1.13.6 // indirect
 	github.com/manveru/faker v0.0.0-20171103152722-9fbc68a78c4d // indirect
+	github.com/matttproud/golang_protobuf_extensions v1.0.1 // indirect
 	github.com/pkg/errors v0.9.1 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/prometheus/client_model v0.2.0 // indirect
+	github.com/prometheus/common v0.32.1 // indirect
+	github.com/prometheus/procfs v0.7.3 // indirect
 	github.com/sergi/go-diff v1.2.0 // indirect
 	github.com/smartystreets/assertions v1.2.1 // indirect
 	github.com/xdg-go/pbkdf2 v1.0.0 // indirect
@@ -43,6 +51,7 @@ require (
 	golang.org/x/text v0.3.7 // indirect
 	golang.org/x/tools v0.1.10 // indirect
 	golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1 // indirect
+	google.golang.org/protobuf v1.27.1 // indirect
 	gopkg.in/yaml.v2 v2.4.0 // indirect
 	gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b // indirect
 )

internal/config/config.go

@@ -9,6 +9,7 @@ type Config struct {
 	Executor     executorConfig
 	ListExecutor listExecutorConfig
 	Cache        cacheConfig
+	Metrics      metricsConfig
 
 	LogLevel string `envconfig:"LOG_LEVEL" default:"INFO"`
 }
@@ -45,3 +46,7 @@ type listExecutorConfig struct {
 type cacheConfig struct {
 	Addr string `envconfig:"CACHE_ADDR" required:"true"`
 }
+
+type metricsConfig struct {
+	Addr string `envconfig:"METRICS_ADDR" default:":2112"`
+}