forked from miekg/skydns2
/
server.go
406 lines (362 loc) · 11.7 KB
/
server.go
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// Copyright (c) 2014 The SkyDNS Authors. All rights reserved.
// Use of this source code is governed by The MIT License (MIT) that can be
// found in the LICENSE file.
package main
import (
"log"
"net"
"os"
"os/signal"
"strings"
"sync"
"time"
"github.com/coreos/go-etcd/etcd"
"github.com/miekg/dns"
)
type Server interface {
Start() (*sync.WaitGroup, error)
Stop()
ServeDNS(dns.ResponseWriter, *dns.Msg)
ServeDNSForward(dns.ResponseWriter, *dns.Msg)
// GetRecords
}
type server struct {
nameservers []string // nameservers to forward to
domain string
domainLabels int
client *etcd.Client
waiter *sync.WaitGroup
dnsUDPServer *dns.Server
dnsTCPServer *dns.Server
dnsHandler *dns.ServeMux
DnsAddr string
// DNSSEC key material
PubKey *dns.DNSKEY
KeyTag uint16
PrivKey dns.PrivateKey
ReadTimeout time.Duration
WriteTimeout time.Duration
RoundRobin bool
}
// Newserver returns a new server.
// TODO(miek): multiple ectdAddrs
func NewServer(domain, dnsAddr string, nameservers []string, etcdAddr string) *server {
s := &server{
domain: dns.Fqdn(strings.ToLower(domain)),
domainLabels: dns.CountLabel(dns.Fqdn(domain)),
DnsAddr: dnsAddr,
client: etcd.NewClient([]string{etcdAddr}),
dnsHandler: dns.NewServeMux(),
waiter: new(sync.WaitGroup),
nameservers: nameservers,
}
// DNS
s.dnsHandler.Handle(".", s)
return s
}
// Start starts a DNS server and blocks waiting to be killed.
func (s *server) Start() (*sync.WaitGroup, error) {
log.Printf("initializing server. DNS Addr: %q, Forwarders: %q", s.DnsAddr, s.nameservers)
s.dnsTCPServer = &dns.Server{
Addr: s.DnsAddr,
Net: "tcp",
Handler: s.dnsHandler,
ReadTimeout: s.ReadTimeout,
WriteTimeout: s.WriteTimeout,
}
s.dnsUDPServer = &dns.Server{
Addr: s.DnsAddr,
Net: "udp",
Handler: s.dnsHandler,
ReadTimeout: s.ReadTimeout,
WriteTimeout: s.WriteTimeout,
}
go s.listenAndServe()
s.waiter.Add(1)
go s.run()
return s.waiter, nil
}
// Stop stops a server.
func (s *server) Stop() {
log.Println("Stopping server")
s.waiter.Done()
}
func (s *server) run() {
var sig = make(chan os.Signal)
signal.Notify(sig, os.Interrupt)
for {
select {
case <-sig:
s.Stop()
return
}
}
}
// ServeDNS is the handler for DNS requests, responsible for parsing DNS request, possibly forwarding
// it to a real dns server and returning a response.
func (s *server) ServeDNS(w dns.ResponseWriter, req *dns.Msg) {
//stats.RequestCount.Inc(1)
q := req.Question[0]
// Ensure we lowercase question so that proper matching against anchor domain takes place
q.Name = strings.ToLower(q.Name)
log.Printf("Received DNS Request for %q from %q with type %d", q.Name, w.RemoteAddr(), q.Qtype)
// If the query does not fall in our s.domain, forward it
if !strings.HasSuffix(q.Name, dns.Fqdn(s.domain)) {
s.ServeDNSForward(w, req)
return
}
m := new(dns.Msg)
m.SetReply(req)
m.Authoritative = true
m.RecursionAvailable = true
m.Answer = make([]dns.RR, 0, 10)
defer func() {
// Check if we need to do DNSSEC and sign the reply
if s.PubKey != nil {
if opt := req.IsEdns0(); opt != nil && opt.Do() {
s.nsec(m)
s.sign(m, opt.UDPSize())
}
}
w.WriteMsg(m)
}()
if q.Name == dns.Fqdn(s.domain) {
switch q.Qtype {
case dns.TypeDNSKEY:
if s.PubKey != nil {
m.Answer = append(m.Answer, s.PubKey)
return
}
case dns.TypeSOA:
m.Answer = s.SOA()
return
}
}
if q.Qtype == dns.TypeA || q.Qtype == dns.TypeAAAA {
records, err := s.AddressRecords(q)
if err != nil {
m.SetRcode(req, dns.RcodeNameError)
m.Ns = s.SOA()
return
}
if s.RoundRobin {
// TODO(miek): refactor this out
switch l := uint16(len(records)); l {
case 1:
case 2:
if dns.Id()%2 == 0 {
records[0], records[1] = records[1], records[0]
}
default:
// Do a minimum of l swap, maximum of 4l swaps
for j := 0; j < int(l*(dns.Id()%4+1)); j++ {
q := dns.Id() % l
p := dns.Id() % l
if q == p {
p = (p + 1) % l
}
records[q], records[p] = records[p], records[q]
}
}
}
m.Answer = append(m.Answer, records...)
}
records, extra, err := s.SRVRecords(q)
if err != nil && len(m.Answer) == 0 {
// We are authoritative for this name, but it does not exist: NXDOMAIN
m.SetRcode(req, dns.RcodeNameError)
m.Ns = s.SOA()
return
}
if q.Qtype == dns.TypeANY || q.Qtype == dns.TypeSRV {
m.Answer = append(m.Answer, records...)
m.Extra = append(m.Extra, extra...)
}
if len(m.Answer) == 0 { // Send back a NODATA response
m.Ns = s.SOA()
}
}
// ServeDNSForward forwards a request to a nameservers and returns the response.
func (s *server) ServeDNSForward(w dns.ResponseWriter, req *dns.Msg) {
if len(s.nameservers) == 0 {
log.Printf("Error: Failure to Forward DNS Request, no servers configured %q", dns.ErrServ)
m := new(dns.Msg)
m.SetReply(req)
m.SetRcode(req, dns.RcodeServerFailure)
m.Authoritative = false // no matter what set to false
m.RecursionAvailable = true // and this is still true
w.WriteMsg(m)
return
}
network := "udp"
if _, ok := w.RemoteAddr().(*net.TCPAddr); ok {
network = "tcp"
}
c := &dns.Client{Net: network, ReadTimeout: 5 * time.Second}
// Use request Id for "random" nameserver selection
nsid := int(req.Id) % len(s.nameservers)
try := 0
Redo:
r, _, err := c.Exchange(req, s.nameservers[nsid])
if err == nil {
log.Printf("Forwarded DNS Request %q to %q", req.Question[0].Name, s.nameservers[nsid])
w.WriteMsg(r)
return
}
// Seen an error, this can only mean, "server not reached", try again
// but only if we have not exausted our nameservers
if try < len(s.nameservers) {
log.Printf("Error: Failure to Forward DNS Request %q to %q", err, s.nameservers[nsid])
try++
nsid = (nsid + 1) % len(s.nameservers)
goto Redo
}
log.Printf("Error: Failure to Forward DNS Request %q", err)
m := new(dns.Msg)
m.SetReply(req)
m.SetRcode(req, dns.RcodeServerFailure)
w.WriteMsg(m)
}
func (s *server) AddressRecords(q dns.Question) (records []dns.RR, err error) {
name := strings.ToLower(q.Name)
if name == s.domain {
// talk to etc
/*
for _, m := range s.Members() {
h, _, err = net.SplitHostPort(m)
if err != nil {
return
}
if q.Qtype == dns.TypeA {
records = append(records, &dns.A{Hdr: dns.RR_Header{Name: q.Name, Rrtype: dns.TypeA, Class: dns.ClassINET, Ttl: 15}, A: net.ParseIP(h)})
}
}
*/
}
// Leader should always be listed
if name == "leader."+s.domain || name == "master."+s.domain || name == s.domain {
// TODO(miek): talks to etcd
/*
h, _, err = net.SplitHostPort(s.Leader())
if err != nil {
return
}
if q.Qtype == dns.TypeA {
records = append(records, &dns.A{Hdr: dns.RR_Header{Name: q.Name, Rrtype: dns.TypeA, Class: dns.ClassINET, Ttl: 15}, A: net.ParseIP(h)})
}
*/
return
}
return get(s.client, name, q.Qtype)
}
func (s *server) SRVRecords(q dns.Question) (records []dns.RR, extra []dns.RR, err error) {
/*
var weight uint16
services := make([]msg.Service, 0)
key := strings.TrimSuffix(q.Name, s.domain+".")
services, err = s.registry.Get(key)
if err != nil {
return
}
weight = 0
if len(services) > 0 {
weight = uint16(math.Floor(float64(100 / len(services))))
}
for _, serv := range services {
// TODO: Dynamically set weight
// a Service may have an IP as its Host"name", in this case
// substitute UUID + "." + s.domain+"." an add an A record
// with the name and IP in the additional section.
// TODO(miek): check if resolvers actually grok this
ip := net.ParseIP(serv.Host)
switch {
case ip == nil:
records = append(records, &dns.SRV{Hdr: dns.RR_Header{Name: q.Name, Rrtype: dns.TypeSRV, Class: dns.ClassINET, Ttl: serv.TTL},
Priority: 10, Weight: weight, Port: serv.Port, Target: serv.Host + "."})
continue
case ip.To4() != nil:
extra = append(extra, &dns.A{Hdr: dns.RR_Header{Name: serv.UUID + "." + s.domain + ".", Rrtype: dns.TypeA, Class: dns.ClassINET, Ttl: serv.TTL}, A: ip.To4()})
records = append(records, &dns.SRV{Hdr: dns.RR_Header{Name: q.Name, Rrtype: dns.TypeSRV, Class: dns.ClassINET, Ttl: serv.TTL},
Priority: 10, Weight: weight, Port: serv.Port, Target: serv.UUID + "." + s.domain + "."})
case ip.To16() != nil:
extra = append(extra, &dns.AAAA{Hdr: dns.RR_Header{Name: serv.UUID + "." + s.domain + ".", Rrtype: dns.TypeAAAA, Class: dns.ClassINET, Ttl: serv.TTL}, AAAA: ip.To16()})
records = append(records, &dns.SRV{Hdr: dns.RR_Header{Name: q.Name, Rrtype: dns.TypeSRV, Class: dns.ClassINET, Ttl: serv.TTL},
Priority: 10, Weight: weight, Port: serv.Port, Target: serv.UUID + "." + s.domain + "."})
default:
panic("skydns: internal error")
}
}
// Append matching entries in different region than requested with a higher priority
labels := dns.SplitDomainName(key)
pos := len(labels) - 4
if len(labels) >= 4 && labels[pos] != "*" {
region := labels[pos]
labels[pos] = "*"
// TODO: This is pretty much a copy of the above, and should be abstracted
additionalServices := make([]msg.Service, len(services))
additionalServices, err = s.registry.Get(strings.Join(labels, "."))
if err != nil {
return
}
weight = 0
if len(additionalServices) <= len(services) {
return
}
weight = uint16(math.Floor(float64(100 / (len(additionalServices) - len(services)))))
for _, serv := range additionalServices {
// Exclude entries we already have
if strings.ToLower(serv.Region) == region {
continue
}
// TODO: Dynamically set priority and weight
// TODO(miek): same as above: abstract away
ip := net.ParseIP(serv.Host)
switch {
case ip == nil:
records = append(records, &dns.SRV{Hdr: dns.RR_Header{Name: q.Name, Rrtype: dns.TypeSRV, Class: dns.ClassINET, Ttl: serv.TTL},
Priority: 20, Weight: weight, Port: serv.Port, Target: serv.Host + "."})
continue
case ip.To4() != nil:
extra = append(extra, &dns.A{Hdr: dns.RR_Header{Name: serv.UUID + "." + s.domain + ".", Rrtype: dns.TypeA, Class: dns.ClassINET, Ttl: serv.TTL}, A: ip.To4()})
records = append(records, &dns.SRV{Hdr: dns.RR_Header{Name: q.Name, Rrtype: dns.TypeSRV, Class: dns.ClassINET, Ttl: serv.TTL},
Priority: 20, Weight: weight, Port: serv.Port, Target: serv.UUID + "." + s.domain + "."})
case ip.To16() != nil:
extra = append(extra, &dns.AAAA{Hdr: dns.RR_Header{Name: serv.UUID + "." + s.domain + ".", Rrtype: dns.TypeAAAA, Class: dns.ClassINET, Ttl: serv.TTL}, AAAA: ip.To16()})
records = append(records, &dns.SRV{Hdr: dns.RR_Header{Name: q.Name, Rrtype: dns.TypeSRV, Class: dns.ClassINET, Ttl: serv.TTL},
Priority: 20, Weight: weight, Port: serv.Port, Target: serv.UUID + "." + s.domain + "."})
default:
panic("skydns: internal error")
}
}
}
*/
return
}
// listenAndServe binds to DNS ports and starts accepting connections.
func (s *server) listenAndServe() {
go func() {
err := s.dnsTCPServer.ListenAndServe()
if err != nil {
log.Fatalf("Start %s listener on %s failed:%s", s.dnsTCPServer.Net, s.dnsTCPServer.Addr, err.Error())
}
}()
go func() {
err := s.dnsUDPServer.ListenAndServe()
if err != nil {
log.Fatalf("Start %s listener on %s failed:%s", s.dnsUDPServer.Net, s.dnsUDPServer.Addr, err.Error())
}
}()
}
// SOA return a SOA record for this SkyDNS instance.
func (s *server) SOA() []dns.RR {
soa := &dns.SOA{Hdr: dns.RR_Header{Name: s.domain, Rrtype: dns.TypeSOA, Class: dns.ClassINET, Ttl: 3600},
Ns: "master." + s.domain,
Mbox: "hostmaster." + s.domain,
Serial: uint32(time.Now().Truncate(time.Hour).Unix()),
Refresh: 28800,
Retry: 7200,
Expire: 604800,
Minttl: 60,
}
return []dns.RR{soa}
}