Admission Control

Admission Control in Kubernetes refers to a powerful mechanism that intercepts requests to the API server after authentication and authorization but before object persistence. Admission controllers can validate and/or mutate resources before they are stored in etcd.

Key Characteristics

• Request Interception: Intercepts API requests before persistence
• Validation and Mutation: Can validate or modify resources
• Plugin Architecture: Supports pluggable admission controllers
• Critical Security: Provides critical security controls

Advantages

• Security Enforcement: Enforces security policies and constraints
• Validation: Validates resource configurations before creation
• Mutation: Automatically modifies resources to meet standards
• Policy Compliance: Ensures compliance with organizational policies

Disadvantages

• Performance Impact: Can slow down API requests
• Complexity: Complex to configure and manage
• Failure Impact: Admission controller failures can block API requests
• Debugging Difficulty: Difficult to troubleshoot admission issues

Best Practices

• Use validation controllers for security policies
• Implement proper error handling and logging
• Test admission controllers thoroughly
• Monitor admission controller performance

Use Cases

• Security policy enforcement
• Resource quota enforcement
• Label and annotation enforcement
• Image registry validation