mw/federation: add federation back as separate mw for k8s (#929)

* mw/federaration

This PR add the federation back as a middleware to keep it more
contained from the main kubernetes code.

It also makes parseRequest less import and pushes this functionlity down
in the k.Entries. This minimizes (or tries to) the importance for the
qtype in the query. In the end the qtype checking should only happen
in ServeDNS - but for k8s this might proof difficult.

Numerous other cleanup in code and kubernetes tests.

* up test coverage

middleware/kubernetes/federation.go

@@ -0,0 +1,43 @@
+package kubernetes
+
+import (
+	"strings"
+
+	"github.com/coredns/coredns/middleware/etcd/msg"
+	"github.com/coredns/coredns/request"
+)
+
+// The federation node.Labels keys used.
+const (
+	// TODO: Do not hardcode these labels. Pull them out of the API instead.
+	//
+	// We can get them via ....
+	//   import metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	//     metav1.LabelZoneFailureDomain
+	//     metav1.LabelZoneRegion
+	//
+	// But importing above breaks coredns with flag collision of 'log_dir'
+
+	LabelZone   = "failure-domain.beta.kubernetes.io/zone"
+	LabelRegion = "failure-domain.beta.kubernetes.io/region"
+)
+
+// Federations is used from the federations middleware to return the service that should be
+// returned as a CNAME for federation(s) to work.
+func (k *Kubernetes) Federations(state request.Request, fname, fzone string) (msg.Service, error) {
+	nodeName := k.localNodeName()
+	node, err := k.APIConn.GetNodeByName(nodeName)
+	if err != nil {
+		return msg.Service{}, err
+	}
+	r, err := k.parseRequest(state)
+
+	lz := node.Labels[LabelZone]
+	lr := node.Labels[LabelRegion]
+
+	if r.endpoint == "" {
+		return msg.Service{Host: strings.Join([]string{r.service, r.namespace, fname, r.podOrSvc, lz, lr, fzone}, ".")}, nil
+	}
+
+	return msg.Service{Host: strings.Join([]string{r.endpoint, r.service, r.namespace, fname, r.podOrSvc, lz, lr, fzone}, ".")}, nil
+}