Adding user guides for federation replicasets and namespaces

docs/user-guide/federation/secrets.md

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+---
+---
+
+This guide explains how to use secrets in 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, for example
+[this one](https://github.com/kelseyhightower/kubernetes-cluster-federation)
+by Kelsey Hightower, are also available to help you.
+
+You are also expected to have a basic
+[working knowledge of Kubernetes](/docs/getting-started-guides/) in
+general and [Secrets](/docs/user-guide/secrets/) in particular.
+
+## Overview
+
+Secrets in federation control plane (referred to as "federated secrets" in
+this guide) are very similar to the traditional [Kubernetes
+Secrets](/docs/user-guide/secrets/) providing the same functionality.
+Creating them in the federation control plane ensures that they are synchronized
+across all the clusters in federation.
+
+
+## Creating a Federated Secret
+
+The API for Federated Secret is 100% compatible with the
+API for traditional Kubernetes Secret. You can create a secret by sending
+a request to the federation apiserver.
+
+You can do that using [kubectl](/docs/user-guide/kubectl/kubectl/) by running:
+
+``` shell
+kubectl --context=federation-cluster create -f mysecret.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 secret is created, the federation control plane will create
+a matching secret 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 rs myrs
+```
+
+The above assumes that you have a context named 'gce-asia-east1a'
+configured in your client for your cluster in that zone.
+
+These secrets in underlying clusters will match the federated secret.
+
+
+## Updating a Federated Secret
+
+You can update a federated secret as you would update a Kubernetes
+secret; however, for a federated secret, you must send the request to
+the federation apiserver instead of sending it to a specific Kubernetes cluster.
+The Federation control plan ensures that whenever the federated secret is
+updated, it updates the corresponding secrets in all underlying clusters to
+match it.
+
+## Deleting a Federated Secret
+
+You can delete a federated secret as you would delete a Kubernetes
+secret; however, for a federated secret, 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 rs myrs
+```
+
+Note that at this point, deleting a federated secret will not delete the
+corresponding secrets from underlying clusters.
+You must delete the underlying secrets manually.
+We intend to fix this in the future.