prometheus.go

package hoopsnake

import (
	"context"
	"fmt"
	"log"
	"net/http"
	"os"
	"time"

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

func (s *TailnetSSH) setupPrometheus(ctx context.Context, srv *tsnet.Server) error {
	if s.prometheusAddr == "" {
		return nil
	}
	mux := http.NewServeMux()
	mux.Handle("/metrics", promhttp.Handler())
	listener, err := srv.Listen("tcp", s.prometheusAddr)
	if err != nil {
		return fmt.Errorf("could not listen on prometheus address %v: %w", s.prometheusAddr, err)
	}
	go func() {
		server := http.Server{
			Handler:           mux,
			ReadHeaderTimeout: 1 * time.Second,
		}
		err := server.Serve(listener)
		if err != nil && ctx.Err() == nil {
			// Failed to listen but not asked to shut down:
			log.Printf("Failed to listen on prometheus address: %v", err)
			os.Exit(20)
		}
	}()

	v4, v6 := srv.TailscaleIPs()
	promauto.NewGaugeFunc(prometheus.GaugeOpts{
		Name: "hoopsnake_running",
		Help: "A counter set to 1.0 if hoopsnake is running.",
		ConstLabels: prometheus.Labels{
			"ipv4":     v4.String(),
			"ipv6":     v6.String(),
			"hostname": srv.Hostname,
		},
	}, func() float64 { return 1.0 })
	listenAddr := s.prometheusAddr
	if listenAddr[0] == ':' {
		listenAddr = v4.String() + listenAddr
	}

	log.Printf("Serving prometheus metrics at http://%s/metrics", listenAddr)
	return nil
}