k8s_external can now resolve CNAME returned by AWS ELB/NLB (#3916)

Automatically submitted.

plugin/k8s_external/external.go

@@ -16,6 +16,7 @@ import (
 
 	"github.com/coredns/coredns/plugin"
 	"github.com/coredns/coredns/plugin/etcd/msg"
+	"github.com/coredns/coredns/plugin/pkg/upstream"
 	"github.com/coredns/coredns/request"
 
 	"github.com/miekg/dns"
@@ -39,6 +40,8 @@ type External struct {
 	apex       string
 	ttl        uint32
 
+	upstream *upstream.Upstream
+
 	externalFunc     func(request.Request) ([]msg.Service, int)
 	externalAddrFunc func(request.Request) []dns.RR
 }
@@ -90,9 +93,9 @@ func (e *External) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Ms
 
 	switch state.QType() {
 	case dns.TypeA:
-		m.Answer = e.a(svc, state)
+		m.Answer = e.a(ctx, svc, state)
 	case dns.TypeAAAA:
-		m.Answer = e.aaaa(svc, state)
+		m.Answer = e.aaaa(ctx, svc, state)
 	case dns.TypeSRV:
 		m.Answer, m.Extra = e.srv(svc, state)
 	default:

plugin/k8s_external/external_test.go

@@ -41,6 +41,7 @@ func TestExternal(t *testing.T) {
 		}
 
 		resp := w.Msg
+
 		if resp == nil {
 			t.Fatalf("Test %d, got nil message and no error for %q", i, r.Question[0].Name)
 		}
@@ -147,6 +148,18 @@ var tests = []test.Case{
 			test.SOA("example.com.	5	IN	SOA	ns1.dns.example.com. hostmaster.example.com. 1499347823 7200 1800 86400 5"),
 		},
 	},
+	{
+		Qname: "svc11.testns.example.com.", Qtype: dns.TypeA, Rcode: dns.RcodeSuccess,
+		Answer: []dns.RR{
+			test.A("svc11.testns.example.com.	5	IN	A	1.2.3.4"),
+		},
+	},
+	{
+		Qname: "svc12.testns.example.com.", Qtype: dns.TypeA, Rcode: dns.RcodeSuccess,
+		Answer: []dns.RR{
+			test.CNAME("svc12.testns.example.com.	5	IN	CNAME	dummy.hostname"),
+		},
+	},
 }
 
 type external struct{}
@@ -192,6 +205,24 @@ var svcIndexExternal = map[string][]*object.Service{
 			Ports:       []api.ServicePort{{Name: "http", Protocol: "tcp", Port: 80}},
 		},
 	},
+	"svc11.testns": {
+		{
+			Name:        "svc11",
+			Namespace:   "testns",
+			Type:        api.ServiceTypeLoadBalancer,
+			ExternalIPs: []string{"1.2.3.4"},
+			Ports:       []api.ServicePort{{Name: "http", Protocol: "tcp", Port: 80}},
+		},
+	},
+	"svc12.testns": {
+		{
+			Name:        "svc12",
+			Namespace:   "testns",
+			Type:        api.ServiceTypeLoadBalancer,
+			ExternalIPs: []string{"dummy.hostname"},
+			Ports:       []api.ServicePort{{Name: "http", Protocol: "tcp", Port: 80}},
+		},
+	},
 }
 
 func (external) ServiceList() []*object.Service {

plugin/k8s_external/msg_to_dns.go

@@ -1,6 +1,7 @@
 package external
 
 import (
+	"context"
 	"math"
 
 	"github.com/coredns/coredns/plugin/etcd/msg"
@@ -9,7 +10,7 @@ import (
 	"github.com/miekg/dns"
 )
 
-func (e *External) a(services []msg.Service, state request.Request) (records []dns.RR) {
+func (e *External) a(ctx context.Context, services []msg.Service, state request.Request) (records []dns.RR) {
 	dup := make(map[string]struct{})
 
 	for _, s := range services {
@@ -18,7 +19,13 @@ func (e *External) a(services []msg.Service, state request.Request) (records []d
 
 		switch what {
 		case dns.TypeCNAME:
-			// can't happen
+			rr := s.NewCNAME(state.QName(), s.Host)
+			records = append(records, rr)
+			if resp, err := e.upstream.Lookup(ctx, state, dns.Fqdn(s.Host), dns.TypeA); err == nil {
+				for _, rr := range resp.Answer {
+					records = append(records, rr)
+				}
+			}
 
 		case dns.TypeA:
 			if _, ok := dup[s.Host]; !ok {
@@ -35,7 +42,7 @@ func (e *External) a(services []msg.Service, state request.Request) (records []d
 	return records
 }
 
-func (e *External) aaaa(services []msg.Service, state request.Request) (records []dns.RR) {
+func (e *External) aaaa(ctx context.Context, services []msg.Service, state request.Request) (records []dns.RR) {
 	dup := make(map[string]struct{})
 
 	for _, s := range services {
@@ -44,7 +51,13 @@ func (e *External) aaaa(services []msg.Service, state request.Request) (records
 
 		switch what {
 		case dns.TypeCNAME:
-			// can't happen
+			rr := s.NewCNAME(state.QName(), s.Host)
+			records = append(records, rr)
+			if resp, err := e.upstream.Lookup(ctx, state, dns.Fqdn(s.Host), dns.TypeAAAA); err == nil {
+				for _, rr := range resp.Answer {
+					records = append(records, rr)
+				}
+			}
 
 		case dns.TypeA:
 			// nada

plugin/k8s_external/setup.go

@@ -5,6 +5,7 @@ import (
 
 	"github.com/coredns/coredns/core/dnsserver"
 	"github.com/coredns/coredns/plugin"
+	"github.com/coredns/coredns/plugin/pkg/upstream"
 
 	"github.com/caddyserver/caddy"
 )
@@ -30,6 +31,8 @@ func setup(c *caddy.Controller) error {
 		return nil
 	})
 
+	e.upstream = upstream.New()
+
 	dnsserver.GetConfig(c).AddPlugin(func(next plugin.Handler) plugin.Handler {
 		e.Next = next
 		return e

plugin/kubernetes/object/service.go

@@ -62,7 +62,12 @@ func toService(skipCleanup bool, svc *api.Service) *Service {
 
 	li := copy(s.ExternalIPs, svc.Spec.ExternalIPs)
 	for i, lb := range svc.Status.LoadBalancer.Ingress {
+		if lb.IP != "" {
 			s.ExternalIPs[li+i] = lb.IP
+			continue
+		}
+		s.ExternalIPs[li+i] = lb.Hostname
+
 	}
 
 	if !skipCleanup {