Conflict Between Availability and Security

Availability requires redundant components that can be replaced without stopping the system; Security requires a layered architecture with the most critical assets in innermost layers with strict access controls - redundant, distributed components increase the attack surface and complicate security validation

Explanation

High availability demands redundant components distributed so that parts can fail or be replaced without stopping the system. High security demands a layered structure with critical assets deeply protected and high-level security validation at each layer boundary. Distributing and replicating components for availability increases the number of potential attack surfaces and makes it harder to enforce the strict access controls needed for security. A compromise architecture - perhaps using different patterns for different system parts - is necessary.