Exploring Admission Control in Kubernetes

Overview

Admission Control in Kubernetes refers to a set of plugins that intercept requests to the Kubernetes API server after authentication and authorization. These plugins can modify or validate requests to the API server, ensuring compliance with specific policies or enhancing security.

Documentation

Using Admission Controllers.

Admission Control Plugins

There are several admission control plugins available in Kubernetes, each serving a specific purpose.

Some common plugins include:

NamespaceLifecycle
LimitRanger
ServiceAccount
NodeRestriction
PodSecurityPolicy
ResourceQuota

Steps to Configure Admission Control

Identify Required Plugins

Determine which admission control plugins are necessary for your specific requirements.
Configure kube-apiserver

Admission control plugins are enabled in the kube-apiserver configuration. Locate the kube-apiserver manifest, typically at /etc/kubernetes/manifests/kube-apiserver.yaml. Add the --enable-admission-plugins flag with a comma-separated list of plugins. Example:
```
--enable-admission-plugins=NamespaceLifecycle,LimitRanger,ServiceAccount
```
Restart kube-apiserver

After modifying the kube-apiserver manifest, restart the kube-apiserver process. This is usually handled automatically by Kubernetes when the manifest file is updated.
Verify Plugin Activation

Ensure that the plugins are active and working as expected by observing the API server logs or testing the functionality of the plugins.

Conclusion

Admission Control is a powerful mechanism in Kubernetes for enforcing policies and enhancing the security of the cluster. Properly configuring admission control plugins can help maintain cluster stability and compliance with organizational standards. It is important to understand the implications of each plugin and configure them according to the specific needs of your Kubernetes environment.