The Microservices Front-Door

Amazon API Gateway is a fully managed service that makes it easy for developers to create, publish, maintain, and secure APIs at any scale.

1. Key Features

- **Authentication:** Native support for Cognito, OAuth2, and Custom Authorizers (Lambda).
- **Throttling:** Protect your backend from surges by limiting requests per user.
- **Version Management:** Manage 'Stages' (Dev, Prod) and rollback versions instantly.
- **Transformation:** Use VTL (Velocity Template Language) to transform JSON payloads before they hit your .NET service.

2. REST vs HTTP APIs

REST APIs: Full-featured, supports everything (Usage plans, API keys, etc.).
HTTP APIs: Up to 70% cheaper and lower latency. Use these if you only need basic routing and authentication.

3. Architect Insight

Q: "Should I use API Gateway or just an ALB?"

Architect Answer: "Use **ALB** if you have a high-volume, standard .NET API and you want to keep costs predictable. Use **API Gateway** if you are building a serverless ecosystem (Lambda), need advanced features like API Keys, or want to expose your API to external developers via a professional Developer Portal."