make ignore empty work with ext svc types (#2823)

plugin/kubernetes/handler_ignore_emptyservice_test.go

@@ -19,6 +19,14 @@ var dnsEmptyServiceTestCases = []test.Case{
 			test.SOA("cluster.local.	5	IN	SOA	ns.dns.cluster.local. hostmaster.cluster.local. 1499347823 7200 1800 86400 5"),
 		},
 	},
+	// CNAME to external
+	{
+		Qname: "external.testns.svc.cluster.local.", Qtype: dns.TypeCNAME,
+		Rcode: dns.RcodeSuccess,
+		Answer: []dns.RR{
+			test.CNAME("external.testns.svc.cluster.local.	5	IN	CNAME	ext.interwebs.test."),
+		},
+	},
 }
 
 func TestServeDNSEmptyService(t *testing.T) {

plugin/kubernetes/kubernetes.go

@@ -439,7 +439,9 @@ func (k *Kubernetes) findServices(r recordRequest, zone string) (services []msg.
 			continue
 		}
 
-		if k.opts.ignoreEmptyService && svc.ClusterIP != api.ClusterIPNone {
+		// If "ignore empty_service" option is set and no endpoints exist, return NXDOMAIN unless
+		// it's a headless or externalName service (covered below).
+		if k.opts.ignoreEmptyService && svc.ClusterIP != api.ClusterIPNone && svc.Type != api.ServiceTypeExternalName {
 			// serve NXDOMAIN if no endpoint is able to answer
 			podsCount := 0
 			for _, ep := range endpointsListFunc() {