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dns.go
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dns.go
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// Copyright (c) 2016 by António Meireles <antonio.meireles@reformi.st>.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// adapted from github.com/kubernetes/minikube/pkg/localkube/dns.go
//
package server
import (
"fmt"
"io"
"io/ioutil"
"net"
"os"
"os/exec"
"strings"
"time"
"golang.org/x/net/context"
"github.com/TheNewNormal/corectl/components/host/session"
backendetcd "github.com/skynetservices/skydns/backends/etcd"
skymetrics "github.com/skynetservices/skydns/metrics"
skydns "github.com/skynetservices/skydns/server"
)
var (
RecursiveNameServers = []string{
"8.8.8.8:53",
"8.8.4.4:53",
}
LocalDomainName = "coreos.local"
WatermarkHeader = "#\n# This file is automatically generated " +
"and managed by corectl\n#\n"
EmbeddedDNSport = "15353"
)
type DNSServer struct {
sky runner
dnsServerAddr *net.UDPAddr
done chan struct{}
}
func (d *ServerContext) NewDNSServer(root,
serverAddress string, ns []string) (err error) {
var (
dnsAddress *net.UDPAddr
skyConfig = &skydns.Config{
DnsAddr: serverAddress,
Domain: root,
Nameservers: ns,
MinTtl: 30,
}
resolver *os.File
)
if dnsAddress, err = net.ResolveUDPAddr("udp", serverAddress); err != nil {
return
}
skydns.SetDefaults(skyConfig)
backend := backendetcd.NewBackend(d.EtcdClient, context.Background(),
&backendetcd.Config{
Ttl: skyConfig.Ttl,
Priority: skyConfig.Priority,
})
skyServer := skydns.New(backend, skyConfig)
// setup so prometheus doesn't run into nil
skymetrics.Metrics()
d.DNSServer = &DNSServer{
sky: skyServer,
dnsServerAddr: dnsAddress,
}
// make host visible to the VMs by Name
if err = d.DNSServer.addRecord("corectld",
session.Caller.Network.Address); err != nil {
return
}
// ...
if err = d.DNSServer.addRecord("corectld.ns.dns",
session.Caller.Network.Address); err != nil {
return
}
// transparently expose the embedded DNS server to the macOS host
os.Mkdir("/etc/resolver", 0755)
if resolver, err = os.Create("/etc/resolver/corectld"); err != nil {
return
}
fmt.Fprintf(resolver, WatermarkHeader)
fmt.Fprintf(resolver,
"domain %s\nsearch %s\nnameserver 127.0.0.1\nport %v\n",
root, root, EmbeddedDNSport)
resolver.Close()
if err = d.DNSServer.PortForward(); err != nil {
return
}
d.DNSServer.Start()
return
}
func (dns *DNSServer) PortForward() (err error) {
var pfC, pfR *os.File
if pfC, err =
ioutil.TempFile(session.Caller.TmpDir(), "coreos"); err != nil {
return
}
defer os.Remove(pfC.Name())
if pfR, err =
ioutil.TempFile(session.Caller.TmpDir(), "coreos"); err != nil {
return
}
defer os.Remove(pfR.Name())
fmt.Fprintf(pfC, WatermarkHeader)
fmt.Fprintln(pfC, "rdr-anchor 'corectl-dns-forwarding'")
fmt.Fprintln(pfC, "nat-anchor 'com.apple.internet-sharing' all")
fmt.Fprintln(pfC, "rdr-anchor 'com.apple.internet-sharing' all")
fmt.Fprintf(pfC, "load anchor 'corectl-dns-forwarding' from '%s'\n",
pfR.Name())
pfC.Close()
fmt.Fprintf(pfR, WatermarkHeader)
fmt.Fprintf(pfR, "rdr pass on bridge100 inet proto { tcp udp } "+
"from any to any port = domain -> %s port %v\n",
session.Caller.Network.Address, EmbeddedDNSport)
pfR.Close()
exec.Command("/sbin/pfctl", "-e").Run()
return exec.Command("/sbin/pfctl", "-f", pfC.Name()).Run()
}
func (dns *DNSServer) Start() {
if dns.done != nil {
fmt.Fprint(os.Stderr, pad("DNS server already started"))
return
}
dns.done = make(chan struct{})
go until(dns.sky.Run, os.Stderr, "skydns", 1*time.Second, dns.done)
}
func (dns *DNSServer) Stop() {
teardownService()
// closing chan will prevent servers from restarting but will not kill
// running server
close(dns.done)
}
// runner starts a server returning an error if it stops.
type runner interface {
Run() error
}
func teardownService() {
exec.Command("/sbin/pfctl", "-f", "/etc/pf.conf").Run()
Daemon.DNSServer.rmRecord("corectld", session.Caller.Network.Address)
os.Remove("/etc/resolver/corectld")
}
func invertDomain(in string) (out string) {
s := strings.Split(in, ".")
for x := len(s) - 1; x >= 0; x-- {
out += s[x] + "/"
}
out = strings.TrimSuffix(out, "/")
return
}
func (d *DNSServer) addRecord(hostName string, ip string) (err error) {
fqdn := fmt.Sprintf("%s.%s", hostName, LocalDomainName)
path := fmt.Sprintf("/skydns/%s",
strings.Replace(invertDomain(fqdn), ".", "/", -1))
if _, err = Daemon.EtcdClient.Set(context.Background(), path,
"{\"host\":\""+ip+"\", \"TTL\": 20 }", nil); err != nil {
return
}
// reverse
_, err = Daemon.EtcdClient.Set(context.Background(),
"/skydns/arpa/in-addr/"+strings.Replace(ip, ".", "/", -1),
"{\"host\":\""+fqdn+"\", \"TTL\": 20 }", nil)
return
}
func (d *DNSServer) rmRecord(hostName string, ip string) (err error) {
fqdn := fmt.Sprintf("%s.%s", hostName, LocalDomainName)
path := fmt.Sprintf("/skydns/%s",
strings.Replace(invertDomain(fqdn), ".", "/", -1))
if _, err =
Daemon.EtcdClient.Delete(context.Background(), path, nil); err != nil {
return
}
// reverse
_, err = Daemon.EtcdClient.Delete(context.Background(),
"/skydns/arpa/in-addr/"+strings.Replace(ip, ".", "/", -1), nil)
return
}
// helpers bellow loaned from kubernetes/minikube/blob/master/pkg/util/utils.go
// we don't want to consume them straight as recent changes there bring a
// XXL dep tail
// Until endlessly loops the provided function until a message is received on
// the done channel. The function will wait the duration provided in sleep
// between function calls. Errors will be sent on provider Writer.
func until(fn func() error, w io.Writer,
name string, sleep time.Duration, done <-chan struct{}) {
var exitErr error
for {
select {
case <-done:
return
default:
exitErr = fn()
if exitErr == nil {
fmt.Fprintf(w, pad("%s: Exited with no errors.\n"), name)
} else {
fmt.Fprintf(w, pad("%s: Exit with error: %v"), name, exitErr)
}
// wait provided duration before trying again
time.Sleep(sleep)
}
}
}
func pad(str string) string {
return fmt.Sprint("\n%s\n", str)
}