Understanding Kubernetes Admission Control: Image Signing & Policy Gate

What is Admission Control?

Admission control in Kubernetes refers to the process of validating and modifying API requests before they are accepted by the system. This mechanism ensures that only valid, compliant, and secure resources can be created or updated within a cluster.

The admission control pipeline consists of multiple components, each applying specific policies and constraints to incoming requests.

Image Signing & Policy Gate

In the context of Kubernetes, image signing is crucial for verifying the authenticity and integrity of container images. The Image Signing policy ensures that only images with valid signatures are admitted into the cluster.

The Policy Gate component enforces additional policies such as blocking privileged pods, requiring resource limits, and checking for known vulnerabilities (CVEs) to further secure the environment.

How Admission Control Works

When a container image is pushed to a Kubernetes cluster, it travels along a top-down conveyor belt through the admission control pipeline. Each component in this pipeline checks specific constraints and either admits or rejects the image based on predefined rules.

The validating webhook acts as the final checkpoint where all policies are enforced simultaneously using an AND-of-constraints logic, ensuring that only images meeting all criteria are deployed.

Real-World Applications

Admission control is vital in environments with strict security requirements, such as financial institutions or government agencies. By enforcing image signing and policy checks, these organizations can prevent the deployment of malicious or untrusted images.

Additionally, admission control helps manage resource usage by ensuring that pods are configured with appropriate limits, which can improve overall cluster performance and stability.

Frequently asked questions

Try it live

Everything above runs in your browser — open Kubernetes Admission Control: Image Signing & Policy Gate (2D) and change the parameters while it is running. Nothing is installed, nothing is uploaded, the whole model lives in one tab.