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DNS : Fixes recursors answering the DNS query to properly return the correct response. (#4461) 

* Fixes the DNS recursor properly resolving the requests

* Added a test case for the recursor bug

* Refactored code && added a test case for all failing recursors

* Inner indentation moved into else if check
This commit is contained in:
Siva Prasad 2018-08-02 10:12:52 -04:00 committed by GitHub
parent 496af9061e
commit dcd7d9b015
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GPG Key ID: 4AEE18F83AFDEB23
2 changed files with 77 additions and 2 deletions
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10
agent/dns.go
View File

@ -1302,14 +1302,20 @@ func (d *DNSServer) handleRecurse(resp dns.ResponseWriter, req *dns.Msg) {
var err error
for _, recursor := range d.recursors {
r, rtt, err = c.Exchange(req, recursor)
if err == nil || err == dns.ErrTruncated {
// Check if the response is valid and has the desired Response code
if r != nil && (r.Rcode != dns.RcodeSuccess && r.Rcode != dns.RcodeNameError) {
d.logger.Printf("[DEBUG] dns: recurse RTT for %v (%v) Recursor queried: %v Status returned: %v", q, rtt, recursor, dns.RcodeToString[r.Rcode])
// If we still have recursors to forward the query to,
// we move forward onto the next one else the loop ends
continue
} else if err == nil || err == dns.ErrTruncated {
// Compress the response; we don't know if the incoming
// response was compressed or not, so by not compressing
// we might generate an invalid packet on the way out.
r.Compress = !d.disableCompression.Load().(bool)
// Forward the response
d.logger.Printf("[DEBUG] dns: recurse RTT for %v (%v)", q, rtt)
d.logger.Printf("[DEBUG] dns: recurse RTT for %v (%v) Recursor queried: %v", q, rtt, recursor)
if err := resp.WriteMsg(r); err != nil {
d.logger.Printf("[WARN] dns: failed to respond: %v", err)
}

69
agent/dns_test.go
View File

@ -37,9 +37,15 @@ const (
// the provided reply. This is useful for mocking a DNS recursor with
// an expected result.
func makeRecursor(t *testing.T, answer dns.Msg) *dns.Server {
a := answer
mux := dns.NewServeMux()
mux.HandleFunc(".", func(resp dns.ResponseWriter, msg *dns.Msg) {
// The SetReply function sets the return code of the DNS
// query to SUCCESS
// We need a way to copy the variables not addressed
// in SetReply
answer.SetReply(msg)
answer.Rcode = a.Rcode
if err := resp.WriteMsg(&answer); err != nil {
t.Fatalf("err: %s", err)
}
@ -371,6 +377,69 @@ func TestDNS_NodeLookup_AAAA(t *testing.T) {
}
}
func TestDNSCycleRecursorCheck(t *testing.T) {
t.Parallel()
// Start a DNS recursor that returns a SERVFAIL
server1 := makeRecursor(t, dns.Msg{
MsgHdr: dns.MsgHdr{Rcode: dns.RcodeServerFailure},
})
// Start a DNS recursor that returns the result
defer server1.Shutdown()
server2 := makeRecursor(t, dns.Msg{
MsgHdr: dns.MsgHdr{Rcode: dns.RcodeSuccess},
Answer: []dns.RR{
dnsA("www.google.com", "172.21.45.67"),
},
})
defer server2.Shutdown()
//Mock the agent startup with the necessary configs
agent := NewTestAgent(t.Name(),
`recursors = ["`+server1.Addr+`", "`+server2.Addr+`"]
`)
defer agent.Shutdown()
// DNS Message init
m := new(dns.Msg)
m.SetQuestion("google.com.", dns.TypeA)
// Agent request
client := new(dns.Client)
in, _, _ := client.Exchange(m, agent.DNSAddr())
wantAnswer := []dns.RR{
&dns.A{
Hdr: dns.RR_Header{Name: "www.google.com.", Rrtype: dns.TypeA, Class: dns.ClassINET, Rdlength: 0x4},
A: []byte{0xAC, 0x15, 0x2D, 0x43}, // 172 , 21, 45, 67
},
}
verify.Values(t, "Answer", in.Answer, wantAnswer)
}
func TestDNSCycleRecursorCheckAllFail(t *testing.T) {
t.Parallel()
// Start 3 DNS recursors that returns a REFUSED status
server1 := makeRecursor(t, dns.Msg{
MsgHdr: dns.MsgHdr{Rcode: dns.RcodeRefused},
})
defer server1.Shutdown()
server2 := makeRecursor(t, dns.Msg{
MsgHdr: dns.MsgHdr{Rcode: dns.RcodeRefused},
})
defer server2.Shutdown()
server3 := makeRecursor(t, dns.Msg{
MsgHdr: dns.MsgHdr{Rcode: dns.RcodeRefused},
})
defer server3.Shutdown()
//Mock the agent startup with the necessary configs
agent := NewTestAgent(t.Name(),
`recursors = ["`+server1.Addr+`", "`+server2.Addr+`","`+server3.Addr+`"]
`)
defer agent.Shutdown()
// DNS dummy message initialization
m := new(dns.Msg)
m.SetQuestion("google.com.", dns.TypeA)
// Agent request
client := new(dns.Client)
in, _, _ := client.Exchange(m, agent.DNSAddr())
//Verify if we hit SERVFAIL from Consul
verify.Values(t, "Answer", in.Rcode, dns.RcodeServerFailure)
}
func TestDNS_NodeLookup_CNAME(t *testing.T) {
t.Parallel()
recursor := makeRecursor(t, dns.Msg{