Add HTTP metrics to prometheus

api/router.go

@@ -4,12 +4,44 @@ import (
 	"encoding/json"
 	"net/http"
 
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
 	"github.com/rijdendetreinen/gotrain/stores"
 
 	"github.com/gorilla/mux"
 	log "github.com/sirupsen/logrus"
 )
 
+var (
+	httpDuration = promauto.NewHistogramVec(prometheus.HistogramOpts{
+		Namespace: "gotrain",
+		Subsystem: "http",
+		Name:      "duration",
+		Help:      "Duration of HTTP requests.",
+	}, []string{"path"})
+)
+
+var (
+	httpReqs = promauto.NewCounterVec(prometheus.CounterOpts{
+		Namespace: "gotrain",
+		Subsystem: "http",
+		Name:      "requests",
+		Help:      "HTTP requests",
+	}, []string{"path", "url"})
+)
+
+// prometheusMiddleware implements mux.MiddlewareFunc.
+func prometheusMiddleware(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		route := mux.CurrentRoute(r)
+		path, _ := route.GetPathTemplate()
+		timer := prometheus.NewTimer(httpDuration.WithLabelValues(path))
+		next.ServeHTTP(w, r)
+		timer.ObserveDuration()
+		httpReqs.WithLabelValues(path, r.URL.Path).Add(1)
+	})
+}
+
 // ServeAPI serves the REST API on the given address
 func ServeAPI(address string, exit chan bool) {
 	srv := &http.Server{Addr: address}
@@ -33,6 +65,7 @@ func ServeAPI(address string, exit chan bool) {
 	router.HandleFunc("/v2/services/stats", serviceCounters).Methods("GET")
 	router.HandleFunc("/v2/services/service/{id}/{date}", serviceDetails).Methods("GET")
 
+	router.Use(prometheusMiddleware)
 	srv.Handler = router
 
 	go listenAndServe(srv, exit)

cmd/server.go

@@ -43,11 +43,6 @@ func startServer(cmd *cobra.Command) {
 	replacer := strings.NewReplacer(".", "_")
 	viper.SetEnvKeyReplacer(replacer)
 
-	if viper.GetBool("prometheus.enabled") {
-		prometheus_interface.SetupPrometheus()
-		prometheus_interface.StartPrometheusInterface()
-	}
-
 	signalChan := make(chan os.Signal, 1)
 	shutdownFinished := make(chan struct{})
 
@@ -72,6 +67,11 @@ func startServer(cmd *cobra.Command) {
 	apiAddress := viper.GetString("api.address")
 	go api.ServeAPI(apiAddress, exitRestAPI)
 
+	if viper.GetBool("prometheus.enabled") {
+		prometheus_interface.SetupPrometheus()
+		prometheus_interface.StartPrometheusInterface()
+	}
+
 	setupCleanupScheduler()
 	setupDowntimeDetector()
 	setupAutoSave()