What is an API Gateway, and when would you use it in an architecture?

Short answer: API Gateway is a single entry point for APIs in a microservices architecture. Handles routing, load balancing, authentication, rate limiting, logging, monitoring. Examples: Kong, NGINX, AWS API Gateway, Azure API Management. Use when: You have multiple microservices. Need centralized authentication/security. Need rate limiting or monitoring.

Real-world example (ShopNest)

ShopNest exposes REST APIs for cart and checkout. Controllers stay thin; business rules live in application services.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.