Скачать или смотреть Mastering Kubernetes Dynamic AC | Series Part-5 | Validating admission controller(use cases)

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A Validating Admission Controller in Kubernetes is a type of admission controller that intercepts requests to the Kubernetes API server and can either approve or deny the admission of a resource based on certain validation rules. Unlike Mutating Admission Controllers, which have the ability to modify the content of resources, Validating Admission Controllers focus on ensuring that resources comply with specific policies or conditions.

Here's a detailed description of Validating Admission Controllers:

Overview:
Validation Rules:

Validating Admission Controllers enforce policies by checking whether a resource adheres to specified rules or conditions.
They can validate fields such as labels, annotations, resource limits, and more.
Approval or Denial:

After processing an admission request, a Validating Admission Controller can either approve the request, allowing the resource to be persisted, or deny it, preventing the resource from being stored in the cluster.
Workflow:
Request Handling:

When a user creates or modifies a resource, the API server sends an admission review request to registered Validating Admission Controllers.
Admission Review Process:

The Validating Admission Controller processes the request, applies validation logic, and returns an admission review response.
The response includes an admission verdict (allow or deny) and, if needed, additional information or error messages.
Decision Enforcement:

The API server enforces the decision made by the Validating Admission Controller.
If the decision is to deny, the resource is not persisted in the cluster, and an error is returned to the user.
Use Cases:
Resource Validation:

Validating Admission Controllers can ensure that resources comply with policies related to security, naming conventions, resource utilization, etc.
Examples include validating container images, enforcing resource constraints, or ensuring proper labels are set.
Policy Enforcement:

Organizations can use Validating Admission Controllers to enforce specific policies, such as requiring the presence of certain labels or annotations on resources.
Examples:
Image Validation:

A Validating Admission Controller can verify that only approved container images are used in Pods.
Resource Limits:

It can enforce resource constraints, such as minimum and maximum CPU and memory limits, to ensure proper resource utilization.
Challenges:
Error Handling:

Proper error handling is crucial to ensure that users receive meaningful messages when a validation check fails.
Complexity in Policies:

As policies become more complex, managing and defining validation rules can be challenging and require careful consideration.
Conclusion:
Validating Admission Controllers play a crucial role in ensuring the integrity and compliance of resources in a Kubernetes cluster. They enable organizations to enforce policies and validate resources based on predefined rules. Careful design and testing are necessary to ensure that validation checks are effective without hindering the user experience

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