rushlink/metrics.go

package rushlink

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

	"gitea.hashru.nl/dsprenkels/rushlink/internal/db"
	"github.com/gorilla/mux"
	"github.com/pkg/errors"
	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promhttp"
)

const metricNamespace = "rushlink"

var metricRequestsTotalCounter = prometheus.NewCounterVec(prometheus.CounterOpts{
	Namespace: metricNamespace,
	Subsystem: "http",
	Name:      "requests_total",
	Help:      "How many HTTP requests processed, partitioned by status code and HTTP method.",
}, []string{"code", "method"})

func metricURLsTotal(database *db.Database) float64 {
	var metric float64
	if err := database.Transaction(func(tx *db.Database) error {
		var count int64
		if err := database.Model(&db.Paste{}).Count(&count).Error; err != nil {
			return err
		}
		metric = float64(count)
		return nil
	}); err != nil {
		log.Printf("error: %v", errors.Wrap(err, "fetching pastes_total metric"))
		return 0
	}
	return metric
}

// StartMetricsServer starts sering Prometheus metrics exports on addr
func StartMetricsServer(addr string, database *db.Database, fs *db.FileStore) {
	prometheus.MustRegister(metricRequestsTotalCounter)

	prometheus.MustRegister(prometheus.NewGaugeFunc(prometheus.GaugeOpts{
		Namespace: metricNamespace,
		Subsystem: "pastes",
		Name:      "urls_total",
		Help:      "The current amount of pastes in the database.",
	}, func() float64 { return metricURLsTotal(database) }))

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