Stupidly simple Go application instrumented with prometheus

main.go

package main

import (
	"log"
	"net/http"

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

func main() {
	http.HandleFunc("/horse", handleHorse)
	http.HandleFunc("/unicorn", handleUnicorn)

	http.Handle("/metrics", promhttp.Handler())

	log.Fatal(http.ListenAndServe(":8080", nil))
}

func handleHorse(w http.ResponseWriter, _ *http.Request) {
	log.Println("horse request")
	defer log.Println("horse response")

	HorseCountMetric.Inc()

	w.WriteHeader(200)
	w.Write([]byte("HORSE"))
}

func handleUnicorn(w http.ResponseWriter, _ *http.Request) {
	log.Println("unicorn request")
	defer log.Println("unicorn response")

	UnicornCountMetric.Inc()

	w.WriteHeader(200)
	w.Write([]byte("UNICORN"))
}

var (
	HorseCountMetric = promauto.NewCounter(prometheus.CounterOpts{
		Name: "horse_count",
	})
	UnicornCountMetric = promauto.NewCounter(prometheus.CounterOpts{
		Name: "unicorn_count",
	})
)

prometheus.yml

---
global:
  scrape_interval: 5s
  evaluation_interval: 10s

scrape_configs:
  - job_name: example-app
    static_configs:
      - targets: ['host.docker.internal:8080']