HTTP server that increments counter and serves the page with the counter rendered. Useful for verification if you've component that fetch external content with TTL.

main.go

package main

import (
	"flag"
	"fmt"
	"log"
	"net/http"
	"time"
)

var (
	listen   = flag.String("listen", ":8080", "HTTP listen address")
	interval = flag.Duration("interval", time.Minute, "Interval to update the counter")
	counter  = 0
)

func main() {
	flag.Parse()

	// Update counter.
	every(*interval, incrementCounter)

	// HTTP handlers.
	http.HandleFunc("/", handler)
	log.Printf("Starting server %s\n", *listen)
	log.Fatal(http.ListenAndServe(*listen, nil))
}

func handler(w http.ResponseWriter, r *http.Request) {
	fmt.Fprintf(w, "<h1>Counter: %d</h1>", counter)
}

func every(dur time.Duration, fn func()) {
	time.AfterFunc(dur, func() {
		fn()
		every(dur, fn)
	})
}

func incrementCounter() {
	counter += 1
	log.Printf("Counter incremented by one, its value now: %d\n", counter)
}