Add documentation for federated config map

docs/user-guide/federation/configmap.md

@@ -0,0 +1,86 @@
+---
+---
+
+This guide explains how to use ConfigMaps in a Federation control plane.
+
+* TOC
+{:toc}
+
+## Prerequisites
+
+This guide assumes that you have a running Kubernetes Cluster
+Federation installation. If not, then head over to the
+[federation admin guide](/docs/admin/federation/) to learn how to
+bring up a cluster federation (or have your cluster administrator do
+this for you).
+Other tutorials, such as Kelsey Hightower's 
+[Federated Kubernetes Tutorial](https://github.com/kelseyhightower/kubernetes-cluster-federation),
+might also help you create a Federated Kubernetes cluster.
+
+You should also have a basic
+[working knowledge of Kubernetes](/docs/getting-started-guides/) in
+general and [ConfigMaps](/docs/user-guide/ConfigMaps/) in particular.
+
+## Overview
+
+Federated ConfigMaps are very similar to the traditional [Kubernetes
+ConfigMaps](/docs/user-guide/configmap/) and provide the same functionality.
+Creating them in the federation control plane ensures that they are synchronized
+across all the clusters in federation.
+
+
+## Creating a Federated ConfigMap
+
+The API for Federated ConfigMap is 100% compatible with the
+API for traditional Kubernetes ConfigMap. You can create a ConfigMap by sending
+a request to the federation apiserver.
+
+You can do that using [kubectl](/docs/user-guide/kubectl/) by running:
+
+``` shell
+kubectl --context=federation-cluster create -f myconfigmap.yaml
+```
+
+The `--context=federation-cluster` flag tells kubectl to submit the
+request to the Federation apiserver instead of sending it to a kubernetes
+cluster.
+
+Once a Federated ConfigMap is created, the federation control plane will create
+a matching ConfigMap in all underlying kubernetes clusters.
+You can verify this by checking each of the underlying clusters, for example:
+
+``` shell
+kubectl --context=gce-asia-east1a get configmap myconfigmap
+```
+
+The above assumes that you have a context named 'gce-asia-east1a'
+configured in your client for your cluster in that zone.
+
+These ConfigMaps in underlying clusters will match the Federated ConfigMap.
+
+
+## Updating a Federated ConfigMap
+
+You can update a Federated ConfigMap as you would update a Kubernetes
+ConfigMap; however, for a Federated ConfigMap, you must send the request to
+the federation apiserver instead of sending it to a specific Kubernetes cluster.
+The federation control plane ensures that whenever the Federated ConfigMap is
+updated, it updates the corresponding ConfigMaps in all underlying clusters to
+match it.
+
+## Deleting a Federated ConfigMap
+
+You can delete a Federated ConfigMap as you would delete a Kubernetes
+ConfigMap; however, for a Federated ConfigMap, you must send the request to
+the federation apiserver instead of sending it to a specific Kubernetes cluster.
+
+For example, you can do that using kubectl by running:
+
+```shell
+kubectl --context=federation-cluster delete configmap 
+```
+
+Note that at this point, deleting a Federated ConfigMap will not delete the
+corresponding ConfigMaps from underlying clusters.
+You must delete the underlying ConfigMaps manually.
+We intend to fix this in the future.