An API Gateway improves both security and performance in a microservices system by acting as the single, controlled entry point for all client traffic before it reaches internal services.
Key Points: • It centralizes authentication and authorization, verifying tokens or credentials once at the edge instead of every client needing to trust every internal service directly. • It shields internal services from direct exposure to the internet, reducing the attack surface since only the gateway needs to be internet-facing. • For performance, it can load-balance requests across service instances, cache frequent responses, and aggregate multiple backend calls into a single client-facing response. • Rate limiting at the gateway protects backend services from being overwhelmed by excessive or abusive traffic. • It reduces the number of round trips a client needs to make by handling request routing and composition centrally rather than requiring clients to call multiple services directly.
Example: Spring Cloud Gateway sitting in front of ten microservices can validate a JWT once per request, apply a rate limit of 100 requests per minute per client, and cache a frequently requested product listing response, all before the request ever reaches a backend service.
Interview Tip: A concise interview answer is:
"The gateway centralizes security by validating authentication once at the edge and hiding internal services from direct exposure, and it improves performance through load balancing, caching, and rate limiting. It effectively becomes the one place I harden and optimize instead of duplicating that logic across every individual service."