Handle K8s middleware NS record (#662)

* commit for testing in cluster

* commit for testing in cluster

* refactor and add ns.dns record

* Release 007

* reduce heap allocations

* gofmt

* revert accidental Makefile commits

* restore prior rcode for disabled pod mode

* revert Makefile deltas

* add unit tests

* more unit tests

* make isRequestInReverseRange easier to test

* more unit tests

* addressing review feedback

* commit setup.go

1 files changed, 115 insertions, 0 deletions

diff --git a/middleware/kubernetes/ns.go b/middleware/kubernetes/ns.go
new file mode 100644
index 000000000..7f7736abc
--- /dev/null
+++ b/middleware/kubernetes/ns.go
@@ -0,0 +1,115 @@
+package kubernetes
+
+import (
+	"net"
+	"strings"
+
+	"github.com/coredns/coredns/middleware/etcd/msg"
+
+	"github.com/miekg/dns"
+	"k8s.io/client-go/1.5/pkg/api"
+)
+
+const DefaultNSName = "ns.dns."
+
+var corednsRecord dns.A
+
+type InterfaceAddrser interface {
+	InterfaceAddrs() ([]net.Addr, error)
+}
+
+type InterfaceAddrs struct{}
+
+func (i InterfaceAddrs) InterfaceAddrs() ([]net.Addr, error) {
+	return net.InterfaceAddrs()
+}
+
+func (k *Kubernetes) recordsForNS(r recordRequest, svcs *[]msg.Service) error {
+	ns := k.CoreDNSRecord()
+	s := msg.Service{
+		Host: ns.A.String(),
+		Key:  msg.Path(strings.Join([]string{ns.Hdr.Name, r.zone}, "."), "coredns")}
+	*svcs = append(*svcs, s)
+	return nil
+}
+
+// DefaultNSMsg returns an msg.Service representing an A record for
+// ns.dns.[zone] -> dns service ip. This A record is needed to legitimize
+// the SOA response in middleware.NS(), which is hardcoded at ns.dns.[zone].
+func (k *Kubernetes) defaultNSMsg(r recordRequest) msg.Service {
+	ns := k.CoreDNSRecord()
+	s := msg.Service{
+		Key:  msg.Path(strings.Join([]string{DefaultNSName, r.zone}, "."), "coredns"),
+		Host: ns.A.String(),
+	}
+	return s
+}
+
+func isDefaultNS(name string, r recordRequest) bool {
+	return strings.Index(name, DefaultNSName) == 0 && strings.Index(name, r.zone) == len(DefaultNSName)
+}
+
+func (k *Kubernetes) CoreDNSRecord() dns.A {
+	var localIP net.IP
+	var svcName string
+	var svcNamespace string
+	var dnsIP net.IP
+
+	if len(corednsRecord.Hdr.Name) == 0 || corednsRecord.A == nil {
+		// get local Pod IP
+		addrs, _ := k.interfaceAddrs.InterfaceAddrs()
+
+		for _, addr := range addrs {
+			ip, _, _ := net.ParseCIDR(addr.String())
+			ip = ip.To4()
+
+			if ip == nil || ip.IsLoopback() {
+				continue
+			}
+			localIP = ip
+			break
+		}
+		// Find endpoint matching IP to get service and namespace
+		endpointsList := k.APIConn.EndpointsList()
+
+	FindEndpoint:
+		for _, ep := range endpointsList.Items {
+			for _, eps := range ep.Subsets {
+				for _, addr := range eps.Addresses {
+					if localIP.Equal(net.ParseIP(addr.IP)) {
+
+						svcNamespace = ep.ObjectMeta.Namespace
+						svcName = ep.ObjectMeta.Name
+						break FindEndpoint
+					}
+				}
+			}
+		}
+
+		if len(svcName) == 0 {
+			corednsRecord.Hdr.Name = DefaultNSName
+			corednsRecord.A = localIP
+			return corednsRecord
+		}
+		// Find service to get ClusterIP
+		serviceList := k.APIConn.ServiceList()
+	FindService:
+		for _, svc := range serviceList {
+			if svcName == svc.Name && svcNamespace == svc.Namespace {
+				if svc.Spec.ClusterIP == api.ClusterIPNone {
+					dnsIP = localIP
+				} else {
+					dnsIP = net.ParseIP(svc.Spec.ClusterIP)
+				}
+				break FindService
+			}
+		}
+		if dnsIP == nil {
+			dnsIP = localIP
+		}
+
+		corednsRecord.Hdr.Name = strings.Join([]string{svcName, svcNamespace, "svc."}, ".")
+		corednsRecord.A = dnsIP
+	}
+	return corednsRecord
+}