Admission Controllers

Admission Controllers in Kubernetes are a crucial aspect of securing and governing the behavior of your clusters. They provide a way to intercept and modify Kubernetes API requests, enabling you to implement additional control and validation mechanisms. These controllers are invoked every time a resource is created, updated, or deleted within the cluster.

How Admission Controllers Work

Admission Controllers in Kubernetes are executed in a specific order, allowing you to define a chain of checks and modifications. Each controller can either allow or deny the request based on its specific rules and logic. If a controller denies the request, the operation is blocked, and the API server returns an error message. This process ensures that all resources created or modified within the cluster meet the defined criteria and security standards.

Why Use Admission Controllers?

There are numerous reasons why Admission Controllers are beneficial in Kubernetes environments:

• Enhanced Security: Controllers can enforce security policies, such as Pod Security Standards, to prevent the creation of vulnerable or malicious containers.
• Improved Resource Management: Controllers like Resource Quota and LimitRange can manage resource usage, ensuring that resources are allocated fairly and preventing resource exhaustion.
• Policy Enforcement: Admission Controllers can implement custom policies, such as enforcing specific labels or annotations on resources, to maintain consistency and compliance within the cluster.
• Auditing and Logging: Controllers can log and audit API requests, providing valuable insights into cluster activity and potential security threats.

Types of Admission Controllers

Kubernetes offers two primary types of Admission Controllers: