This week’s ByteByteGo system design refresher dissects the crucial differences between load balancers and API gateways, two often-confused components in modern architecture. While both sit between clients and backend servers, their core functions diverge significantly. A load balancer’s sole job is traffic distribution, handling health checks, failover, and L4/L7 routing to ensure no single server is overwhelmed.

An API gateway, however, acts as a smart front-end controller, managing authentication, rate limiting, request aggregation, observability, and request/response transformation before traffic even reaches the load balancer. Their synergy is key: the gateway handles smart routing and security, while the load balancer efficiently distributes the traffic load across backend instances. This distinction prevents architectural pitfalls where mixing their responsibilities causes performance bottlenecks and security gaps.