Add Prometheus metrics

src/main.go

@@ -3,6 +3,7 @@ package main
 import (
 	"fmt"
 	"log"
+	"net/http"
 	"os"
 	"strconv"
 	"time"
@@ -13,14 +14,26 @@ import (
 	"github.com/mineatar-io/api-server/src/redis"
 	"github.com/mineatar-io/api-server/src/routes"
 	"github.com/mineatar-io/api-server/src/util"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 	"github.com/valyala/fasthttp"
 )
 
 var (
-	host   string              = "127.0.0.1"
-	port   uint16              = 3000
-	config *conf.Configuration = &conf.Configuration{}
-	r      *redis.Redis        = &redis.Redis{}
+	host           string              = "127.0.0.1"
+	port           uint16              = 3000
+	prometheusHost string              = "127.0.0.1"
+	prometheusPort uint16              = 3001
+	config         *conf.Configuration = &conf.Configuration{}
+	r              *redis.Redis        = &redis.Redis{}
+)
+
+var (
+	requestCountMetric = promauto.NewCounter(prometheus.CounterOpts{
+		Name: "request_count",
+		Help: "The total number of requests received",
+	})
 )
 
 func init() {
@@ -42,6 +55,11 @@ func init() {
 
 	if value, ok := os.LookupEnv("HOST"); ok {
 		host = value
+		prometheusHost = value
+	}
+
+	if value, ok := os.LookupEnv("PROM_HOST"); ok {
+		prometheusHost = value
 	}
 
 	if value, ok := os.LookupEnv("PORT"); ok {
@@ -52,6 +70,17 @@ func init() {
 		}
 
 		port = uint16(parsedValue)
+		prometheusPort = uint16(parsedValue + 1)
+	}
+
+	if value, ok := os.LookupEnv("PROM_PORT"); ok {
+		parsedValue, err := strconv.ParseUint(value, 10, 16)
+
+		if err != nil {
+			log.Fatal(err)
+		}
+
+		prometheusPort = uint16(parsedValue)
 	}
 
 	routes.Init(r, config)
@@ -69,10 +98,19 @@ func middleware(next fasthttp.RequestHandler) fasthttp.RequestHandler {
 			log.Printf("%s %s (%s) - %s\n", ctx.Method(), ctx.URI(), ctx.RemoteAddr(), ctx.UserAgent())
 		}
 
+		requestCountMetric.Inc()
+
 		next(ctx)
 	}
 }
 
+func metrics() {
+	log.Printf("Prometheus listening on %s:%d\n", prometheusHost, prometheusPort)
+
+	http.Handle("/metrics", promhttp.Handler())
+	http.ListenAndServe(fmt.Sprintf("%s:%d", prometheusHost, prometheusPort), nil)
+}
+
 func main() {
 	defer r.Close()
 
@@ -91,5 +129,7 @@ func main() {
 
 	log.Printf("Listening on %s:%d\n", host, port)
 
+	go metrics()
+
 	log.Fatal(fasthttp.ListenAndServe(fmt.Sprintf("%s:%d", host, port), middleware(router.Handler)))
 }