An API Gateway manages traffic by routing each request to the right service, distributing load evenly, and applying rate limiting and caching to keep the system stable under load.
Key Points: • It routes requests based on path, host, or headers to the correct backend service, hiding the internal topology from clients. • It load balances across multiple instances of a service so no single instance gets overwhelmed while others sit idle. • Rate limiting caps how many requests a client can make in a given time window, protecting backend services from being overloaded during traffic spikes. • Response caching for frequently requested, slow-changing data reduces the number of calls that actually reach backend services. • Some gateways also handle request throttling, retries, and circuit breaking at the edge, adding another layer of resilience before traffic even reaches a service.
Example: During a flash sale, an API Gateway in front of a Product service can rate-limit each client to a fixed number of requests per second and cache the product catalog response for a few seconds, so a sudden traffic spike doesn't overwhelm the Product service's database.
Interview Tip: A concise interview answer is:
"An API Gateway manages traffic by routing requests to the correct service, load balancing across instances, rate limiting to protect backends from spikes, and caching common responses to cut down on redundant load. It acts as a traffic-control layer at the edge before requests ever reach the actual services."