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Simplify DNS server startup check #833

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merged 2 commits into from
Apr 1, 2015
Merged

Simplify DNS server startup check #833

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65ada1a
Use DNS server startup callbacks
mgood Mar 31, 2015
062e4f9
Remove unnecessary DNS test entry
mgood Mar 31, 2015
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91 changes: 21 additions & 70 deletions command/agent/dns.go
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Original file line number Diff line number Diff line change
Expand Up @@ -7,15 +7,14 @@ import (
"math/rand"
"net"
"strings"
"sync"
"time"

"github.com/hashicorp/consul/consul/structs"
"github.com/miekg/dns"
)

const (
testQuery = "_test.consul."
consulDomain = "consul."
maxServiceResponses = 3 // For UDP only
maxRecurseRecords = 3
)
Expand Down Expand Up @@ -51,17 +50,21 @@ func NewDNSServer(agent *Agent, config *DNSConfig, logOutput io.Writer, domain s
// Construct the DNS components
mux := dns.NewServeMux()

var wg sync.WaitGroup

// Setup the servers
server := &dns.Server{
Addr: bind,
Net: "udp",
Handler: mux,
UDPSize: 65535,
Addr: bind,
Net: "udp",
Handler: mux,
UDPSize: 65535,
NotifyStartedFunc: wg.Done,
}
serverTCP := &dns.Server{
Addr: bind,
Net: "tcp",
Handler: mux,
Addr: bind,
Net: "tcp",
Handler: mux,
NotifyStartedFunc: wg.Done,
}

// Create the server
Expand All @@ -79,11 +82,8 @@ func NewDNSServer(agent *Agent, config *DNSConfig, logOutput io.Writer, domain s
// Register mux handler, for reverse lookup
mux.HandleFunc("arpa.", srv.handlePtr)

// Register mux handlers, always handle "consul."
// Register mux handlers
mux.HandleFunc(domain, srv.handleQuery)
if domain != consulDomain {
mux.HandleFunc(consulDomain, srv.handleTest)
}
if len(recursors) > 0 {
validatedRecursors := make([]string, len(recursors))

Expand All @@ -99,6 +99,8 @@ func NewDNSServer(agent *Agent, config *DNSConfig, logOutput io.Writer, domain s
mux.HandleFunc(".", srv.handleRecurse)
}

wg.Add(2)

// Async start the DNS Servers, handle a potential error
errCh := make(chan error, 1)
go func() {
Expand All @@ -116,28 +118,11 @@ func NewDNSServer(agent *Agent, config *DNSConfig, logOutput io.Writer, domain s
}
}()

// Check the server is running, do a test lookup
checkCh := make(chan error, 1)
// Wait for NotifyStartedFunc callbacks indicating server has started
startCh := make(chan struct{})
go func() {
// This is jank, but we have no way to edge trigger on
// the start of our server, so we just wait and hope it is up.
time.Sleep(50 * time.Millisecond)

m := new(dns.Msg)
m.SetQuestion(testQuery, dns.TypeANY)

c := new(dns.Client)
in, _, err := c.Exchange(m, bind)
if err != nil {
checkCh <- fmt.Errorf("dns test query failed: %v", err)
return
}

if len(in.Answer) == 0 {
checkCh <- fmt.Errorf("no response to test message")
return
}
close(checkCh)
wg.Wait()
close(startCh)
}()

// Wait for either the check, listen error, or timeout
Expand All @@ -146,8 +131,8 @@ func NewDNSServer(agent *Agent, config *DNSConfig, logOutput io.Writer, domain s
return srv, e
case e := <-errChTCP:
return srv, e
case e := <-checkCh:
return srv, e
case <-startCh:
return srv, nil
case <-time.After(time.Second):
return srv, fmt.Errorf("timeout setting up DNS server")
}
Expand Down Expand Up @@ -234,12 +219,6 @@ func (d *DNSServer) handleQuery(resp dns.ResponseWriter, req *dns.Msg) {
d.logger.Printf("[DEBUG] dns: request for %v (%v)", q, time.Now().Sub(s))
}(time.Now())

// Check if this is potentially a test query
if q.Name == testQuery {
d.handleTest(resp, req)
return
}

// Switch to TCP if the client is
network := "udp"
if _, ok := resp.RemoteAddr().(*net.TCPAddr); ok {
Expand All @@ -266,34 +245,6 @@ func (d *DNSServer) handleQuery(resp dns.ResponseWriter, req *dns.Msg) {
}
}

// handleTest is used to handle DNS queries in the ".consul." domain
func (d *DNSServer) handleTest(resp dns.ResponseWriter, req *dns.Msg) {
q := req.Question[0]
defer func(s time.Time) {
d.logger.Printf("[DEBUG] dns: request for %v (%v)", q, time.Now().Sub(s))
}(time.Now())

if !(q.Qtype == dns.TypeANY || q.Qtype == dns.TypeTXT) {
return
}
if q.Name != testQuery {
return
}

// Always respond with TXT "ok"
m := new(dns.Msg)
m.SetReply(req)
m.Authoritative = true
m.RecursionAvailable = true
header := dns.RR_Header{Name: q.Name, Rrtype: dns.TypeTXT, Class: dns.ClassINET, Ttl: 0}
txt := &dns.TXT{Hdr: header, Txt: []string{"ok"}}
m.Answer = append(m.Answer, txt)
d.addSOA(consulDomain, m)
if err := resp.WriteMsg(m); err != nil {
d.logger.Printf("[WARN] dns: failed to respond: %v", err)
}
}

// addSOA is used to add an SOA record to a message for the given domain
func (d *DNSServer) addSOA(domain string, msg *dns.Msg) {
soa := &dns.SOA{
Expand Down
28 changes: 0 additions & 28 deletions command/agent/dns_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -39,34 +39,6 @@ func TestRecursorAddr(t *testing.T) {
}
}

func TestDNS_IsAlive(t *testing.T) {
dir, srv := makeDNSServer(t)
defer os.RemoveAll(dir)
defer srv.agent.Shutdown()

m := new(dns.Msg)
m.SetQuestion("_test.consul.", dns.TypeANY)

c := new(dns.Client)
addr, _ := srv.agent.config.ClientListener("", srv.agent.config.Ports.DNS)
in, _, err := c.Exchange(m, addr.String())
if err != nil {
t.Fatalf("err: %v", err)
}

if len(in.Answer) != 1 {
t.Fatalf("Bad: %#v", in)
}

txt, ok := in.Answer[0].(*dns.TXT)
if !ok {
t.Fatalf("Bad: %#v", in.Answer[0])
}
if txt.Txt[0] != "ok" {
t.Fatalf("Bad: %#v", in.Answer[0])
}
}

func TestDNS_NodeLookup(t *testing.T) {
dir, srv := makeDNSServer(t)
defer os.RemoveAll(dir)
Expand Down