From 24e2d5de00f6dbd3df7a932425fb21bc0cd715b6 Mon Sep 17 00:00:00 2001
From: Michael Stapelberg <stapelberg@google.com>
Date: Mon, 18 Jun 2018 08:04:56 +0200
Subject: [PATCH] dnsd: serve prometheus metrics on port 8053

---
 cmd/dnsd/dnsd.go                | 23 +++++++++++++++++++++++
 internal/dns/dns.go             | 22 ++++++++++++++++++++--
 internal/netconfig/netconfig.go |  9 +++++++--
 3 files changed, 50 insertions(+), 4 deletions(-)

diff --git a/cmd/dnsd/dnsd.go b/cmd/dnsd/dnsd.go
index ce0a50a..f7122dd 100644
--- a/cmd/dnsd/dnsd.go
+++ b/cmd/dnsd/dnsd.go
@@ -6,15 +6,33 @@ import (
 	"flag"
 	"io/ioutil"
 	"log"
+	"net/http"
 	"os"
 	"os/signal"
 	"syscall"
 
+	"github.com/gokrazy/gokrazy"
+
 	"router7/internal/dhcp4d"
 	"router7/internal/dns"
+	"router7/internal/multilisten"
 	"router7/internal/netconfig"
+
+	_ "net/http/pprof"
 )
 
+func updateListeners() error {
+	hosts, err := gokrazy.PrivateInterfaceAddrs()
+	if err != nil {
+		return err
+	}
+	if net1, err := multilisten.IPv6Net1("/perm"); err == nil {
+		hosts = append(hosts, net1)
+	}
+
+	return multilisten.ListenAndServe(hosts, "8053", http.DefaultServeMux)
+}
+
 func logic() error {
 	// TODO: set correct upstream DNS resolver(s)
 	ip, err := netconfig.LinkAddress("/perm", "lan0")
@@ -37,10 +55,15 @@ func logic() error {
 	if err := readLeases(); err != nil {
 		log.Printf("cannot resolve DHCP hostnames: %v", err)
 	}
+	http.Handle("/metrics", srv.PrometheusHandler())
+	updateListeners()
 	ch := make(chan os.Signal, 1)
 	signal.Notify(ch, syscall.SIGUSR1)
 	go func() {
 		for range ch {
+			if err := updateListeners(); err != nil {
+				log.Printf("updateListeners: %v", err)
+			}
 			if err := readLeases(); err != nil {
 				log.Printf("readLeases: %v", err)
 			}
diff --git a/internal/dns/dns.go b/internal/dns/dns.go
index 05e1a16..61e0def 100644
--- a/internal/dns/dns.go
+++ b/internal/dns/dns.go
@@ -3,6 +3,7 @@ package dns
 import (
 	"log"
 	"net"
+	"net/http"
 	"os"
 	"strings"
 	"sync"
@@ -10,9 +11,10 @@ import (
 
 	"router7/internal/dhcp4d"
 
-	"golang.org/x/time/rate"
-
 	"github.com/miekg/dns"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+	"golang.org/x/time/rate"
 )
 
 type Server struct {
@@ -21,6 +23,10 @@ type Server struct {
 	domain    string
 	upstream  string
 	sometimes *rate.Limiter
+	prom      struct {
+		registry *prometheus.Registry
+		queries  prometheus.Counter
+	}
 
 	mu           sync.Mutex
 	hostname, ip string
@@ -40,6 +46,13 @@ func NewServer(addr, domain string) *Server {
 		hostname:  hostname,
 		ip:        ip,
 	}
+	server.prom.registry = prometheus.NewRegistry()
+	server.prom.queries = prometheus.NewCounter(prometheus.CounterOpts{
+		Name: "dns_queries",
+		Help: "Number of DNS queries received",
+	})
+	server.prom.registry.MustRegister(server.prom.queries)
+	server.prom.registry.MustRegister(prometheus.NewGoCollector())
 	server.initHostsLocked()
 	dns.HandleFunc(".", server.handleRequest)
 	return server
@@ -68,6 +81,10 @@ func (s *Server) hostByIP(n string) (string, bool) {
 	return r, ok
 }
 
+func (s *Server) PrometheusHandler() http.Handler {
+	return promhttp.HandlerFor(s.prom.registry, promhttp.HandlerOpts{})
+}
+
 func (s *Server) SetLeases(leases []dhcp4d.Lease) {
 	s.mu.Lock()
 	defer s.mu.Unlock()
@@ -126,6 +143,7 @@ func isLocalInAddrArpa(q string) bool {
 
 // TODO: require search domains to be present, then use HandleFunc("lan.", internalName)
 func (s *Server) handleRequest(w dns.ResponseWriter, r *dns.Msg) {
+	s.prom.queries.Inc()
 	if len(r.Question) == 1 { // TODO: answer all questions we can answer
 		q := r.Question[0]
 		if q.Qtype == dns.TypeA && q.Qclass == dns.ClassINET {
diff --git a/internal/netconfig/netconfig.go b/internal/netconfig/netconfig.go
index 14f19c2..efc469f 100644
--- a/internal/netconfig/netconfig.go
+++ b/internal/netconfig/netconfig.go
@@ -547,8 +547,13 @@ func Apply(dir, root string) error {
 		}
 	}
 
-	if err := notify.Process("/user/dyndns", syscall.SIGUSR1); err != nil {
-		log.Printf("notifying dyndns: %v", err)
+	for _, process := range []string{
+		"dyndns", // depends on the public IPv4 address
+		"dnsd",   // listens on private IPv4/IPv6 and public IPv6Net1
+	} {
+		if err := notify.Process("/user/"+process, syscall.SIGUSR1); err != nil {
+			log.Printf("notifying %s: %v", process, err)
+		}
 	}
 
 	if err := applySysctl(); err != nil {