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.
Worked example: a single entry point in front of many backend services that handles cross-cutting concerns — auth, rate-limiting, routing, request aggregation — so each service does not re-implement them. Gotcha: it centralizes logic but can become a bottleneck and a deploy chokepoint (every team waits on the gateway); keep it thin — routing and policy, not business logic — or it turns into a distributed monolith.