API Gateway
An API Gateway is a server that sits in front of one or more backend services, acting as a single entry point that handles routing, authentication, rate limiting, and other cross-cutting concerns for API traffic.
Definition
An API Gateway is a server that sits in front of one or more backend services, acting as a single entry point that handles routing, authentication, rate limiting, and other cross-cutting concerns for API traffic.
Overview
An API Gateway centralizes the cross-cutting logic that would otherwise be duplicated across many backend services, particularly in a Microservices architecture where dozens of independently deployed services might each need authentication, logging, and Rate Limiting. Instead of every service implementing these concerns individually, clients call the gateway, and the gateway routes each request to the appropriate backend service. Beyond routing, API gateways commonly handle authentication and token validation, request/response transformation (for example, aggregating several backend calls into one client-facing response — a pattern closely related to a BFF (Backend for Frontend)), caching, and enforcing API Versioning policies. Many gateways also expose observability data like request logs and latency metrics, and can apply resilience patterns such as the Circuit Breaker Pattern to protect backend services from cascading failures. Gateways range from open-source, self-hosted options to fully managed cloud services, and are frequently paired with OpenAPI or Swagger definitions to validate incoming requests against a documented API contract before they ever reach a backend service.
Key Concepts
- Single entry point routing requests to multiple backend services
- Centralized authentication and token validation
- Rate limiting and traffic throttling per client or API key
- Request/response transformation and aggregation
- API versioning and backward-compatibility management
- Caching of frequent responses to reduce backend load
- Observability: centralized logging, metrics, and tracing
- Resilience features like circuit breaking and retries