unstable.go

// A Web server with two endpoints - /stable (returning 200) and /unstable (going into failing state with defined probability every tick and returning 500 while in it)
// Based on Googles slo-burn code https://github.com/google/prometheus-slo-burn-example/tree/master/server

package main

import (
	"fmt"
	"math/rand"
	"net/http"
	"os"
	"strconv"
	"time"

	"github.com/go-chi/chi"
	"github.com/go-chi/chi/middleware"
)

func main() {
	var failing bool // Indicator of whether the service is in failing state
	const tick = time.Second
	const faultProbability float32 = 0.005 // 74% chance of not failing in a minute
	const maxFaultDuration int = 60        // In ticks

	go func() {
		var faultDuration int
		for {
			if failing {
				faultDuration = rand.Intn(maxFaultDuration) + 1
				time.Sleep(time.Duration(faultDuration) * tick)
				fmt.Print("Recovered at ", time.Now().Format(time.RFC3339), "\n")
				failing = false
			} else {
				if rand.Float32() < faultProbability {
					fmt.Print("Failed at ", time.Now().Format(time.RFC3339), "\n")
					failing = true
				}
				time.Sleep(tick)
			}
		}
	}()

	r := chi.NewRouter()
	r.Use(middleware.RequestID)
	r.Use(middleware.Logger)
	r.Use(middleware.Recoverer)

	r.Get("/stable", func(w http.ResponseWriter, r *http.Request) {
		w.Write([]byte("200 - serving"))
	})

	r.Get("/unstable", func(w http.ResponseWriter, r *http.Request) {
		if failing {
			w.WriteHeader(http.StatusInternalServerError)
			w.Write([]byte("500 - in failing state"))
		} else {
			w.Write([]byte("200 - serving"))
		}
	})

	var port string // port # for the HTTP listener

	portNumber, err := strconv.ParseInt(os.Getenv("PORT"), 0, 16)
	if err == nil && portNumber > 0 && portNumber < 65536 {
		port = fmt.Sprintf("%d", portNumber)
	} else {
		port = "8080"
	}
	fmt.Printf("Starting up on http://localhost:%s\n", port)
	http.ListenAndServe(":"+port, r)
}