// Copyright 2015 The Prometheus Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// A minimal example of exposing Prometheus metrics from a Go application.
package main

import (
	"flag"
	"log"
	"net/http"

	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/collectors"
	"github.com/prometheus/client_golang/prometheus/promhttp"
)

// Address for exposing Prometheus metrics.
var addr = flag.String("listen-address", ":8080", "The address to listen on for HTTP requests.")

func main() {
	flag.Parse()

	// Create a custom registry instead of using the global default registry.
	// This helps isolate application metrics from automatically registered metrics.
	reg := prometheus.NewRegistry()

	// Register Go runtime metrics (such as goroutine count
	// and GC statistics) and process-level metrics (such as
	// CPU and memory usage).
	reg.MustRegister(
		collectors.NewGoCollector(),
		collectors.NewProcessCollector(collectors.ProcessCollectorOpts{}),
	)

	// Expose the registered metrics at /metrics for Prometheus scraping.
	http.Handle("/metrics", promhttp.HandlerFor(reg, promhttp.HandlerOpts{Registry: reg}))

	log.Fatal(http.ListenAndServe(*addr, nil))
}