Metricer

metricer.go

// Overcomplicated "healthy" metric generator
package main

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

type metric struct {
	name  string
	value int
}

var getmetrics func(chan<- metric)

func envmetrics(channel chan<- metric) {
	healthy, err := strconv.Atoi(os.Getenv("HEALTHY"))
	if err != nil {
		healthy = 0
	}
	channel <- metric{name: "healthy", value: healthy}
	close(channel)
}

func randmetrics(failpct int) func(chan<- metric) {
	seed := rand.NewSource(time.Now().UnixNano())
	rs := rand.New(seed)
	return func(channel chan<- metric) {
		val := rs.Intn(100)
		if val < failpct {
			val = 0
		} else {
			val = 1
		}
		channel <- metric{name: "healthy", value: val}
		close(channel)
	}
}

func timedmetrics(frequency int, failpct int) func(chan<- metric) {
	// Start at a random offset in the frequency
	seed := rand.NewSource(time.Now().UnixNano())
	rs := rand.New(seed)
	offset := rs.Intn(frequency)

	start := time.Now().Add(-time.Duration(offset) * time.Second)

	return func(channel chan<- metric) {
		elapsedsecs := int(time.Since(start).Seconds())
		cyclepos := elapsedsecs % frequency
		var val int
		if (float64(cyclepos)/float64(frequency))*100.0 < float64(failpct) {
			val = 0
		} else {
			val = 1
		}
		channel <- metric{name: "healthy", value: val}
		close(channel)
	}
}

func metricHandler(w http.ResponseWriter, r *http.Request) {
	channel := make(chan metric)
	go getmetrics(channel)
	for m := range channel {
		fmt.Fprintf(w, "%s %d\r\n", m.name, m.value)
	}
}

func main() {
	switch len(os.Args) {
	case 3:
		frequency, err := strconv.Atoi(os.Args[1])
		if err != nil {
			panic(err)
		}
		failpct, err := strconv.Atoi(os.Args[2])
		if err != nil {
			panic(err)
		}
		getmetrics = timedmetrics(frequency, failpct)
		fmt.Printf("Timed mode, loop every %d seconds, failure rate at %d%%\n", frequency, failpct)
	case 2:
		failpct, err := strconv.Atoi(os.Args[1])
		if err != nil {
			panic(err)
		}
		getmetrics = randmetrics(failpct)
		fmt.Printf("Random mode, failure rate at %d%%\n", failpct)
	default:
		getmetrics = envmetrics
		fmt.Println("Reporting based on HEALTHY from environment")
	}
	http.HandleFunc("/metrics", metricHandler)
	http.ListenAndServe(":8080", nil)
}