Merge pull request #288 from gmr/rfc-2782-srv-lookups

Add RFC-2782 style SRV lookups
hashicorp · Aug 18, 2014 · ca1aeb8 · ca1aeb8
2 parents 869d7aa + b030991
commit ca1aeb8
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Showing 3 changed files with 205 additions and 12 deletions.
diff --git a/command/agent/dns.go b/command/agent/dns.go
@@ -266,17 +266,32 @@ PARSE:
 			goto INVALID
 		}
 
-		// Extract the service
-		service := labels[n-2]
+		// Support RFC 2782 style syntax
+		if n == 3 && strings.HasPrefix(labels[n-2], "_") && strings.HasPrefix(labels[n-3], "_") {
 
-		// Support "." in the label, re-join all the parts
-		tag := ""
-		if n >= 3 {
-			tag = strings.Join(labels[:n-2], ".")
-		}
+			// Grab the tag since we make nuke it if it's tcp
+			tag := labels[n-2][1:]
+
+			// Treat _name._tcp.service.consul as a default, no need to filter on that tag
+			if tag == "tcp" {
+				tag = ""
+			}
+
+			// _name._tag.service.consul
+			d.serviceLookup(network, datacenter, labels[n-3][1:], tag, req, resp)
 
-		// Handle lookup with and without tag
-		d.serviceLookup(network, datacenter, service, tag, req, resp)
+		// Consul 0.3 and prior format for SRV queries
+		} else {
+
+			// Support "." in the label, re-join all the parts
+			tag := ""
+			if n >= 3 {
+				tag = strings.Join(labels[:n-2], ".")
+			}
+
+			// tag[.tag].name.service.consul
+			d.serviceLookup(network, datacenter, labels[n-2], tag, req, resp)
+		}
 
 	case "node":
 		if len(labels) == 1 {

diff --git a/command/agent/dns_test.go b/command/agent/dns_test.go
@@ -1120,3 +1120,137 @@ func TestDNS_ServiceLookup_TTL(t *testing.T) {
 		t.Fatalf("Bad: %#v", in.Extra[0])
 	}
 }
+
+func TestDNS_ServiceLookup_SRV_RFC(t *testing.T) {
+	dir, srv := makeDNSServer(t)
+	defer os.RemoveAll(dir)
+	defer srv.agent.Shutdown()
+
+	testutil.WaitForLeader(t, srv.agent.RPC, "dc1")
+
+	// Register node
+	args := &structs.RegisterRequest{
+		Datacenter: "dc1",
+		Node:       "foo",
+		Address:    "127.0.0.1",
+		Service: &structs.NodeService{
+			Service: "db",
+			Tags:    []string{"master"},
+			Port:    12345,
+		},
+	}
+
+	var out struct{}
+	if err := srv.agent.RPC("Catalog.Register", args, &out); err != nil {
+		t.Fatalf("err: %v", err)
+	}
+
+	m := new(dns.Msg)
+	m.SetQuestion("_db._master.service.consul.", dns.TypeSRV)
+
+	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)
+	}
+
+	srvRec, ok := in.Answer[0].(*dns.SRV)
+	if !ok {
+		t.Fatalf("Bad: %#v", in.Answer[0])
+	}
+	if srvRec.Port != 12345 {
+		t.Fatalf("Bad: %#v", srvRec)
+	}
+	if srvRec.Target != "foo.node.dc1.consul." {
+		t.Fatalf("Bad: %#v", srvRec)
+	}
+	if srvRec.Hdr.Ttl != 0 {
+		t.Fatalf("Bad: %#v", in.Answer[0])
+	}
+
+	aRec, ok := in.Extra[0].(*dns.A)
+	if !ok {
+		t.Fatalf("Bad: %#v", in.Extra[0])
+	}
+	if aRec.Hdr.Name != "foo.node.dc1.consul." {
+		t.Fatalf("Bad: %#v", in.Extra[0])
+	}
+	if aRec.A.String() != "127.0.0.1" {
+		t.Fatalf("Bad: %#v", in.Extra[0])
+	}
+	if aRec.Hdr.Ttl != 0 {
+		t.Fatalf("Bad: %#v", in.Extra[0])
+	}
+}
+
+func TestDNS_ServiceLookup_SRV_RFC_TCP_Default(t *testing.T) {
+	dir, srv := makeDNSServer(t)
+	defer os.RemoveAll(dir)
+	defer srv.agent.Shutdown()
+
+	testutil.WaitForLeader(t, srv.agent.RPC, "dc1")
+
+	// Register node
+	args := &structs.RegisterRequest{
+		Datacenter: "dc1",
+		Node:       "foo",
+		Address:    "127.0.0.1",
+		Service: &structs.NodeService{
+			Service: "db",
+			Tags:    []string{"master"},
+			Port:    12345,
+		},
+	}
+
+	var out struct{}
+	if err := srv.agent.RPC("Catalog.Register", args, &out); err != nil {
+		t.Fatalf("err: %v", err)
+	}
+
+	m := new(dns.Msg)
+	m.SetQuestion("_db._tcp.service.consul.", dns.TypeSRV)
+
+	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)
+	}
+
+	srvRec, ok := in.Answer[0].(*dns.SRV)
+	if !ok {
+		t.Fatalf("Bad: %#v", in.Answer[0])
+	}
+	if srvRec.Port != 12345 {
+		t.Fatalf("Bad: %#v", srvRec)
+	}
+	if srvRec.Target != "foo.node.dc1.consul." {
+		t.Fatalf("Bad: %#v", srvRec)
+	}
+	if srvRec.Hdr.Ttl != 0 {
+		t.Fatalf("Bad: %#v", in.Answer[0])
+	}
+
+	aRec, ok := in.Extra[0].(*dns.A)
+	if !ok {
+		t.Fatalf("Bad: %#v", in.Extra[0])
+	}
+	if aRec.Hdr.Name != "foo.node.dc1.consul." {
+		t.Fatalf("Bad: %#v", in.Extra[0])
+	}
+	if aRec.A.String() != "127.0.0.1" {
+		t.Fatalf("Bad: %#v", in.Extra[0])
+	}
+	if aRec.Hdr.Ttl != 0 {
+		t.Fatalf("Bad: %#v", in.Extra[0])
+	}
+}
diff --git a/website/source/docs/agent/dns.html.markdown b/website/source/docs/agent/dns.html.markdown
@@ -73,9 +73,14 @@ the node.
 ## Service Lookups
 
 A service lookup is the alternate type of query. It is used to query for service
-providers. The format of a service lookup is like the following:
+providers and supports two mode of lookup, a strict RCF style lookup and the
+standard lookup.
 
-    <tag>.<service>.service.<datacenter>.<domain>
+### Standard Style Lookup
+
+The format of a standard service lookup is like the following:
+
+    [tag.]<service>.service[.datacenter][.domain]
 
 As with node lookups, the `datacenter` is optional, as is the `tag`. If no tag is
 provided, then no filtering is done on tag. So, if we want to find any redis service
@@ -114,6 +119,46 @@ SRV records.
     ;; ADDITIONAL SECTION:
     foobar.node.dc1.consul.	0	IN	A	10.1.10.12
 
+### RFC-2782 Style Lookup
+
+The format for RFC style lookups uses the following format:
+
+  _<service>._<protocol>.service[.datacenter][.domain]
+
+Per [RFC-2782](https://www.ietf.org/rfc/rfc2782.txt), SRV queries should use
+underscores (_) as a prefix to the `service` and `protocol` values in a query to
+prevent DNS collisions. The `protocol` value can be any of the tags for a
+service or if the service has no tags, the value "tcp" should be used. If "tcp"
+is specified as the protocol, the query will not perform any tag filtering.
+
+Other than the query format and default "tcp" protocol/tag value, the behavior
+of the RFC style lookup is the same as the standard style of lookup.
+
+Using the RCF style lookup, If you registered the service "rabbitmq" on port
+5672 and tagged it with "amqp" you would query the SRV record as
+"_rabbitmq._amqp.service.consul" as illustrated in the example below:
+
+    $ dig @127.0.0.1 -p 8600 consul.service.consul SRV
+
+    ; <<>> DiG 9.8.3-P1 <<>> @127.0.0.1 -p 8600 _rabbitmq._amqp.service.consul ANY
+    ; (1 server found)
+    ;; global options: +cmd
+    ;; Got answer:
+    ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 52838
+    ;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
+    ;; WARNING: recursion requested but not available
+
+    ;; QUESTION SECTION:
+    ;_rabbitmq._amqp.service.consul.	IN	SRV
+
+    ;; ANSWER SECTION:
+    _rabbitmq._amqp.service.consul.	0	IN	SRV	1 1 5672 rabbitmq.node1.dc1.consul.
+
+    ;; ADDITIONAL SECTION:
+    rabbitmq.node1.dc1.consul.	0	IN	A	10.1.11.20
+
+### UDP Based DNS Queries
+
 When the DNS query is performed using UDP, Consul will truncate the results
 without setting the truncate bit. This is to prevent a redundant lookup over
 TCP which generate additional load. If the lookup is done over TCP, the results
@@ -125,4 +170,3 @@ By default, all DNS results served by Consul set a 0 TTL value. This disables
 caching of DNS results. However, there are many situations in which caching is
 desirable for performance and scalability. This is discussed more in the guide
 for [DNS Caching](/docs/guides/dns-cache.html).
-