API Gateway

Overview

API Gateway is an intermediary service that receives API traffic and applies routing, authentication, policy, transformation, rate limiting, or observability before forwarding it. It differs from a payment gateway, which provides payment acceptance and financial processing rather than general API traffic management.

A typical implementation works as follows: The gateway terminates client connections, validates identity and policy, selects a backend, forwards or transforms the request, and returns the response. Data handled by API Gateway should use documented types, units, timestamp rules, nullable fields, and enum behavior to prevent silent interpretation errors.

Common risks include misconfiguration and excessive trust. It is used to centralize cross-cutting controls and expose a stable entry point to backend services. Important failure modes include misconfiguration, excessive trust, hidden transformations, single-point failure, insecure plugins, and inconsistent authorization. These failures can affect every service behind it.

Core controls require teams to use least privilege, independent backend authorization, configuration review, high availability, safe limits, trace propagation, and tested bypass prevention. For API Gateway, the application should preserve a correlation path from request construction through response, asynchronous completion, and final business state.

Operational evidence should include request ID, client, policy result, route, backend, latency, status, configuration version, and rate-limit decision. API Gateway should be documented alongside API Path, API Monitoring, and API Failover.

Testing API Gateway should cover malformed input, denied access, rate limits, timeouts, duplicates, asynchronous completion, and version changes. The API Gateway owner should publish stable error semantics and guidance on whether correction, retry, status lookup, or escalation is appropriate.