API gateway

An API gateway is a server that sits in front of your backend services and acts as a single entry point for inbound client requests. It typically handles request routing, composition and protocol translation, and can add cross-cutting concerns such as authentication, rate limiting, caching and load balancing. By centralizing these concerns, an API gateway lets backend services evolve independently behind a stable, controlled front door.

How HARP relates to an API gateway

HARP is a forward proxy, so it sits on the opposite side of the conversation. An API gateway is a reverse proxy that manages traffic coming into your APIs, while HARP manages the requests your application sends out to the remote APIs it consumes. The two are complementary: a gateway protects and shapes your inbound surface, and HARP brings reliability, performance and observability to your outbound dependencies without changing application code.

If your goal is to control, cache, observe and add resilience to the external APIs your application calls, that is the forward proxy role HARP is built for, not an API gateway in front of your own services.