Make the Prometheus port configurable

This enables people to run more than one worker (without containers) on one machine.

Resolves #3

worker/main.go

@@ -16,6 +16,7 @@ import (
 )
 
 var config common.WorkerConf
+var prometheusPort int
 var debug, trace bool
 
 func init() {
@@ -28,6 +29,7 @@ func init() {
 func main() {
 	var serverAddress string
 	flag.StringVar(&serverAddress, "s", "", "Gosbench Server IP and Port in the form '192.168.1.1:2000'")
+	flag.IntVar(&prometheusPort, "p", 8888, "Port on which the Prometheus Exporter will be available. Default: 8888")
 	flag.BoolVar(&debug, "d", false, "enable debug log output")
 	flag.BoolVar(&trace, "t", false, "enable trace log output")
 	flag.Parse()

worker/s3.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"context"
+	"fmt"
 	"io"
 	"net/http"
 
@@ -50,7 +51,8 @@ func init() {
 		mux := http.NewServeMux()
 		mux.Handle("/metrics", pe)
 		// http://localhost:8888/metrics
-		if err := http.ListenAndServe(":8888", mux); err != nil {
+		log.Infof("Starting Prometheus Exporter on port %d", prometheusPort)
+		if err := http.ListenAndServe(fmt.Sprintf(":%d", prometheusPort), mux); err != nil {
 			log.WithError(err).Fatalf("Failed to run Prometheus /metrics endpoint:")
 		}
 	}()