main.go

package main

import (
	"fmt"
	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promhttp"
	"log"
	"net/http"
	"time"
)

func main() {
	requestCountMetric := prometheus.NewCounterVec(prometheus.CounterOpts{
		Namespace: "hello_server",
		Name:      "request_count",
	}, []string{"method", "path"})
	err := prometheus.Register(requestCountMetric)
	if err != nil {
		log.Fatalf("Could not register requestCountMetric: %v", err)
	}
	defer prometheus.Unregister(requestCountMetric)
	
	requestDurationMetric := prometheus.NewSummaryVec(prometheus.SummaryOpts{
		Namespace: "hello_server",
		Name:      "request_duration",
	}, []string{"method", "path"})
	err = prometheus.Register(requestDurationMetric)
	if err != nil {
		log.Fatalf("Could not register requestDurationMetric: %v", err)
	}
	defer prometheus.Unregister(requestDurationMetric)

	http.HandleFunc("/hello", func(w http.ResponseWriter, r *http.Request) {
		requestCountMetric.WithLabelValues(r.Method, "/hello").Add(1)
		startTime := time.Now()
		defer func() {
			requestDurationMetric.WithLabelValues(r.Method, "/hello").Observe(time.Since(startTime).Seconds())
		}()
		fmt.Println("Received request for /hello")
		fmt.Fprintln(w, "Hello World")
	})

	http.Handle("/metrics", promhttp.Handler())
	port := ":8080"
	log.Printf("Server started on %s", port)
	log.Fatal(http.ListenAndServe(port, nil))
}