An API Gateway is a server that acts as a single entry point for requests coming into a microservices-based application. It sits between the client and backend services, routing requests, handling security, rate limiting, and response formatting.

Why use an API Gateway? In microservices architecture, clients would otherwise need to communicate with each microservice directly. This creates complexity and security issues. An API Gateway solves this by:

• Hiding internal service structure from clients.
• Aggregating multiple service calls into one.
• Enforcing authentication and throttling policies.
• Supporting logging, analytics, and monitoring.

Common features:

• Request routing and load balancing.
• SSL termination and CORS handling.
• Token-based authentication (e.g., JWT).
• Caching and compression for performance.

Popular API Gateways:

• Kong
• NGINX
• AWS API Gateway
• Apigee
• Zuul (Netflix)

API Gateways simplify client interaction and enforce cross-cutting concerns in one place. For anyone working in backend or full-stack development, understanding API Gateway architecture is crucial to delivering scalable and secure applications.