Revert "Document admission control plug-ins for Kube 1.0"

docs/admission_controllers.md

-# Admission Controllers
-
-## What are they?
-
-An admission control plug-in is a piece of code that intercepts requests to the Kubernetes
-API server prior to persistence of the object.  The plug-in code is in the API server process
-and must be compiled into the binary in order to be used at this time.
-
-Each admission control plug-in is run in sequence before a request is accepted into the cluster.  If
-any of the plug-ins in the sequence reject the request, the entire request is rejected immediately
-and an error is returned to the end-user.
-
-Admission control plug-ins may mutate the incoming object in some cases to apply system configured
-defaults.  In addition, admission control plug-ins may mutate related resources as part of request
-processing to do things like increment quota usage.
-
-## Why do I need them?
-
-Many advanced features in Kubernetes require an admission control plug-in to be enabled in order
-to properly support the feature.  As a result, a Kubernetes API server that is not properly
-configured with the right set of admission control plug-ins is an incomplete server and will not
-support all the features you expect.
-
-## How do I turn on an admission control plug-in?
-
-The Kubernetes API server supports a flag, ```admission_control``` that takes a comma-delimited,
-ordered list of admission control choices to invoke prior to modifying objects in the cluster.
-
-## What does each plug-in do?
-
-### AlwaysAdmit
-
-This plug-in will accept all incoming requests made to the Kubernetes API server.
-
-### AlwaysDeny
-
-This plug-in will reject all mutating requests made to the Kubernetes API server.  It's largely intended
-for testing purposes and is not recommended for usage in a real deployment.
-
-### DenyExecOnPrivileged
-
-This plug-in will intercept all requests to exec a command in a pod if that pod has a privileged container.
-
-If your cluster supports privileged containers, and you want to restrict the ability of end-users to exec
-commands in those containers, we strongly encourage enabling this plug-in.
-
-### ServiceAccount
-
-This plug-in limits admission of Pod creation requests based on the Pod's ```ServiceAccount```.
-
-1. If the pod does not have a ```ServiceAccount```, it modifies the pod's ```ServiceAccount``` to "default".
-2. It ensures that the ```ServiceAccount``` referenced by a pod exists.
-3. If ```LimitSecretReferences``` is true, it rejects the pod if the pod references ```Secret``` objects which the pods
-```ServiceAccount``` does not reference.
-4. If the pod does not contain any ```ImagePullSecrets```, the ```ImagePullSecrets``` of the
-```ServiceAccount``` are added to the pod.
-5. If ```MountServiceAccountToken``` is true, it adds a ```VolumeMount``` with the pod's
-```ServiceAccount``` API token secret to containers in the pod.
-
-We strongly recommend using this plug-in if you intend to make use of Kubernetes ```ServiceAccount``` objects.
-
-### SecurityContextDeny
-
-This plug-in will deny any ```SecurityContext``` that defines options that were not available on the ```Container```.
-
-### ResourceQuota
-
-This plug-in will observe the incoming request and ensure that it does not violate any of the constraints
-enumerated in the ```ResourceQuota``` object in a ```Namespace```.  If you are using ```ResourceQuota```
-objects in your Kubernetes deployment, you MUST use this plug-in to enforce quota constraints.
-
-It is strongly encouraged that this plug-in is configured last in the sequence of admission control plug-ins.  This is
-so that quota is not prematurely incremented only for the request to be rejected later in admission control.
-
-### LimitRanger
-
-This plug-in will observe the incoming request and ensure that it does not violate any of the constraints
-enumerated in the ```LimitRange``` object in a ```Namespace```.  If you are using ```LimitRange``` objects in
-your Kubernetes deployment, you MUST use this plug-in to enforce those constraints.
-
-### NamespaceExists
-
-This plug-in will observe all incoming requests that attempt to create a resource in a Kubernetes ```Namespace```
-and reject the request if the ```Namespace``` was not previously created.  We strongly recommend running
-this plug-in to ensure integrity of your data.
-
-### NamespaceAutoProvision (deprecated)
-
-This plug-in will observe all incoming requests that attempt to create a resource in a Kubernetes ```Namespace```
-and create a new ```Namespace``` if one did not already exist previously.
-
-We strongly recommend ```NamespaceExists``` over ```NamespaceAutoProvision```.
-
-### NamespaceLifecycle
-
-This plug-in enforces that a ```Namespace``` that is undergoing termination cannot have new content created in it.
-
-A ```Namespace``` deletion kicks off a sequence of operations that remove all content (pods, services, etc.) in that
-namespace.  In order to enforce integrity of that process, we strongly recommend running this plug-in.
-
-Once ```NamespaceAutoProvision``` is deprecated, we anticipate ```NamespaceLifecycle``` and ```NamespaceExists``` will
-be merged into a single plug-in that enforces the life-cycle of a ```Namespace``` in Kubernetes.
-
-## Is there a recommended set of plug-ins to use?
-
-Yes.
-
-For Kubernetes 1.0, we strongly recommend running the following set of admission control plug-ins:
-
-```shell
---admission_control=NamespaceLifecycle,NamespaceExists,LimitRanger,SecurityContextDeny,ServiceAccount,ResourceQuota
-```