rushlink/metrics/metrics.go

package metrics

import (
	"log"
	"net/http"
	"time"

	"github.com/gorilla/mux"
	"github.com/pkg/errors"
	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promauto"
	"github.com/prometheus/client_golang/prometheus/promhttp"
	bolt "go.etcd.io/bbolt"

	"gitea.hashru.nl/dsprenkels/rushlink/db"
)

const (
	METRICS_ADDR = "127.0.0.1:58614"
)

func StartMetricsServer() {
	var (
		_ = promauto.NewGaugeFunc(prometheus.GaugeOpts{
			Namespace: "rushlink",
			Subsystem: "shorten",
			Name:      "urls_total",
			Help:      "The current amount of shortened urls in the database.",
		}, func() float64 {
			var metric float64
			if err := db.DB.View(func(tx *bolt.Tx) error {
				bucket := tx.Bucket([]byte("shorten"))
				if bucket == nil {
					return errors.New("bucket 'shorten' could not be found")
				}
				metric = float64(bucket.Stats().KeyN)
				return nil
			}); err != nil {
				log.Printf("error: %v", errors.Wrap(err, "fetching shorten_urls_total metric"))
				return 0
			}
			return metric
		})
	)

	router := mux.NewRouter()
	router.Handle("/metrics", promhttp.Handler()).Methods("GET")
	srv := &http.Server{
		Handler:      router,
		Addr:         METRICS_ADDR,
		WriteTimeout: 15 * time.Second,
		ReadTimeout:  15 * time.Second,
	}
	log.Fatal(srv.ListenAndServe())
}