Kubernetes Registry (#1064)

* add teh k8s registry

* add k8s reg config/cmd

* go mod update

registry/kubernetes/README.md

@@ -0,0 +1,66 @@
+# Kubernetes Registry Plugin for micro
+This is a plugin for go-micro that allows you to use Kubernetes as a registry.
+
+
+## Overview
+This registry plugin makes use of Annotations and Labels on a Kubernetes pod
+to build a service discovery mechanism.
+
+
+## RBAC
+If your Kubernetes cluster has RBAC enabled, a role and role binding
+will need to be created to allow this plugin to `list` and `patch` pods.
+
+A cluster role can be used to specify the `list` and `patch`
+requirements, while a role binding per namespace can be used to apply
+the cluster role. The example RBAC configs below assume your Micro-based
+services are running in the `test` namespace, and the pods that contain
+the services are using the `micro-services` service account.
+
+```
+apiVersion: rbac.authorization.k8s.io/v1
+kind: ClusterRole
+metadata:
+  name: micro-registry
+rules:
+- apiGroups:
+  - ""
+  resources:
+  - pods
+  verbs:
+  - list
+  - patch
+  - watch
+```
+
+```
+apiVersion: rbac.authorization.k8s.io/v1
+kind: RoleBinding
+metadata:
+  name: micro-registry
+roleRef:
+  apiGroup: rbac.authorization.k8s.io
+  kind: ClusterRole
+  name: micro-registry
+subjects:
+- kind: ServiceAccount
+  name: micro-services
+  namespace: test
+```
+
+
+## Gotchas
+* Registering/Deregistering relies on the HOSTNAME Environment Variable, which inside a pod
+is the place where it can be retrieved from. (This needs improving)
+
+
+## Connecting to the Kubernetes API
+### Within a pod
+If the `--registry_address` flag is omitted, the plugin will securely connect to
+the Kubernetes API using the pods "Service Account". No extra configuration is necessary.
+
+Find out more about service accounts here. http://kubernetes.io/docs/user-guide/accessing-the-cluster/
+
+### Outside of Kubernetes
+Some functions of the plugin should work, but its not been heavily tested.
+Currently no TLS support.