Remove the word middleware (#1067)

* Rename middleware to plugin

first pass; mostly used 'sed', few spots where I manually changed
text.

This still builds a coredns binary.

* fmt error

* Rename AddMiddleware to AddPlugin

* Readd AddMiddleware to remain backwards compat

plugin/kubernetes/federation.go

@@ -0,0 +1,45 @@
+package kubernetes
+
+import (
+	"github.com/coredns/coredns/plugin/etcd/msg"
+	"github.com/coredns/coredns/plugin/pkg/dnsutil"
+	"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 plugin 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 := parseRequest(state)
+	if err != nil {
+		return msg.Service{}, err
+	}
+
+	lz := node.Labels[LabelZone]
+	lr := node.Labels[LabelRegion]
+
+	if r.endpoint == "" {
+		return msg.Service{Host: dnsutil.Join([]string{r.service, r.namespace, fname, r.podOrSvc, lz, lr, fzone})}, nil
+	}
+
+	return msg.Service{Host: dnsutil.Join([]string{r.endpoint, r.service, r.namespace, fname, r.podOrSvc, lz, lr, fzone})}, nil
+}