fix kubernetes in-cluster CNAME lookup (#2040)

fix #2038
Signed-off-by: bingshen.wbs <bingshen.wbs@alibaba-inc.com>

plugin/backend_lookup.go

@@ -40,8 +40,9 @@ func A(b ServiceBackend, zone string, state request.Request, previousRecords []d
 			if dnsutil.DuplicateCNAME(newRecord, previousRecords) {
 				continue
 			}
-
+			if dns.IsSubDomain(zone, dns.Fqdn(serv.Host)) {
 				state1 := state.NewWithQuestion(serv.Host, state.QType())
+				state1.Zone = zone
 				nextRecords, err := A(b, zone, state1, append(previousRecords, newRecord), opt)
 
 				if err == nil {
@@ -50,14 +51,11 @@ func A(b ServiceBackend, zone string, state request.Request, previousRecords []d
 						records = append(records, newRecord)
 						records = append(records, nextRecords...)
 					}
+				}
 				continue
 			}
 			// This means we can not complete the CNAME, try to look else where.
 			target := newRecord.Target
-			if dns.IsSubDomain(zone, target) {
-				// We should already have found it
-				continue
-			}
 			// Lookup
 			m1, e1 := b.Lookup(state, target, state.QType())
 			if e1 != nil {
@@ -110,8 +108,9 @@ func AAAA(b ServiceBackend, zone string, state request.Request, previousRecords
 			if dnsutil.DuplicateCNAME(newRecord, previousRecords) {
 				continue
 			}
-
+			if dns.IsSubDomain(zone, dns.Fqdn(serv.Host)) {
 				state1 := state.NewWithQuestion(serv.Host, state.QType())
+				state1.Zone = zone
 				nextRecords, err := AAAA(b, zone, state1, append(previousRecords, newRecord), opt)
 
 				if err == nil {
@@ -120,9 +119,9 @@ func AAAA(b ServiceBackend, zone string, state request.Request, previousRecords
 						records = append(records, newRecord)
 						records = append(records, nextRecords...)
 					}
+				}
 				continue
 			}
-
 			// This means we can not complete the CNAME, try to look else where.
 			target := newRecord.Target
 			m1, e1 := b.Lookup(state, target, state.QType())

plugin/kubernetes/handler_test.go

@@ -183,6 +183,15 @@ var dnsTestCases = []test.Case{
 			test.CNAME("external.testns.svc.cluster.local.	5	IN	CNAME	ext.interwebs.test."),
 		},
 	},
+	// CNAME External To Internal Service
+	{
+		Qname: "external-to-service.testns.svc.cluster.local", Qtype: dns.TypeA,
+		Rcode: dns.RcodeSuccess,
+		Answer: []dns.RR{
+			test.CNAME("external-to-service.testns.svc.cluster.local.	5	IN	CNAME	svc1.testns.svc.cluster.local."),
+			test.A("svc1.testns.svc.cluster.local.	5	IN	A	10.0.0.1"),
+		},
+	},
 	// AAAA Service (with an existing A record, but no AAAA record)
 	{
 		Qname: "svc1.testns.svc.cluster.local.", Qtype: dns.TypeAAAA,
@@ -420,6 +429,21 @@ var svcIndex = map[string][]*api.Service{
 			Type: api.ServiceTypeExternalName,
 		},
 	}},
+	"external-to-service.testns": {{
+		ObjectMeta: meta.ObjectMeta{
+			Name:      "external-to-service",
+			Namespace: "testns",
+		},
+		Spec: api.ServiceSpec{
+			ExternalName: "svc1.testns.svc.cluster.local.",
+			Ports: []api.ServicePort{{
+				Name:     "http",
+				Protocol: "tcp",
+				Port:     80,
+			}},
+			Type: api.ServiceTypeExternalName,
+		},
+	}},
 }
 
 func (APIConnServeTest) SvcIndex(s string) []*api.Service {

plugin/kubernetes/parse_test.go

@@ -14,17 +14,17 @@ func TestParseRequest(t *testing.T) {
 		expected string // output from r.String()
 	}{
 		// valid SRV request
-		{"_http._tcp.webs.mynamespace.svc.inter.webs.test.", "http.tcp..webs.mynamespace.svc"},
+		{"_http._tcp.webs.mynamespace.svc.inter.webs.tests.", "http.tcp..webs.mynamespace.svc"},
 		// wildcard acceptance
-		{"*.any.*.any.svc.inter.webs.test.", "*.any..*.any.svc"},
+		{"*.any.*.any.svc.inter.webs.tests.", "*.any..*.any.svc"},
 		// A request of endpoint
-		{"1-2-3-4.webs.mynamespace.svc.inter.webs.test.", "*.*.1-2-3-4.webs.mynamespace.svc"},
+		{"1-2-3-4.webs.mynamespace.svc.inter.webs.tests.", "*.*.1-2-3-4.webs.mynamespace.svc"},
 		// bare zone
-		{"inter.webs.test.", "....."},
+		{"inter.webs.tests.", "....."},
 		// bare svc type
-		{"svc.inter.webs.test.", "....."},
+		{"svc.inter.webs.tests.", "....."},
 		// bare pod type
-		{"pod.inter.webs.test.", "....."},
+		{"pod.inter.webs.tests.", "....."},
 	}
 	for i, tc := range tests {
 		m := new(dns.Msg)