API Gateway

An API gateway is a server that acts as the single entry point for all API requests from clients to a collection of backend services. It handles cross-cutting concerns including authentication, rate limiting, request routing, response caching, SSL termination, and usage logging.

Rather than each backend service implementing its own authentication and rate limiting, the gateway handles these uniformly for all services behind it. This simplifies service development and creates a single control plane for access policy, monitoring, and security.

API gateways are foundational infrastructure for any API-first product. AWS API Gateway, Kong, and Apigee are popular examples. For developers consuming APIs, the gateway is typically transparent - but its rate limiting behavior, error responses, and caching configuration are worth understanding when debugging unexpected API behavior.