The API Gateway we covered in Week 4 is not a simple HTTP proxy. Three independent product families — REST API, HTTP API, and WebSocket API — implement different paradigms, each with different authentication methods, integration types, and performance characteristics. This review focuses less on reconfirming individual concepts and more on edge cases and selection judgment. DVA-C02 asks not "which service should I use" but "why is this configuration wrong" and "what is the root cause of this error". The scenario questions below are structured with the same kind of compound conditions that appear on the actual exam.