Admission control plug-ins intercept requests to the master API prior to persistence of a resource, but after the request is authenticated and authorized.
Each admission control plug-in is run in sequence before a request is accepted into the cluster. If any plug-in in the sequence rejects the request, the entire request is rejected immediately, and an error is returned to the end-user.
Admission control plug-ins may modify the incoming object in some cases to apply system configured defaults. In addition, admission control plug-ins may modify related resources as part of request processing to do things such as incrementing quota usage.
The OpenShift Enterprise master has a default list of plug-ins that are enabled by default for each type of resource (Kubernetes and OpenShift Enterprise). These are required for the proper functioning of the master. Modifying these lists is not recommended unless you strictly know what you are doing. Future versions of the product may use a different set of plug-ins and may change their ordering. If you do override the default list of plug-ins in the master configuration file, you are responsible for updating it to reflect requirements of newer versions of the OpenShift Enterprise master.
Cluster administrators can configure some admission control plug-ins to control certain behavior, such as: