API Gateway
The single entry point that routes, authenticates, and rate-limits every request before it reaches a backend service.
An API gateway sits in front of a system’s backend services as the one public entry point, handling concerns every request needs — authentication, rate limiting, routing to the right service, sometimes request/response transformation — in one place instead of duplicating that logic into every individual service. It’s also a natural point to add or swap a backend service without changing anything the client sees.