Definition: Service that acts as a single entry point for API consumers, handling routing, authentication, rate limiting, and request transformation.
— Source: NERVICO, Product Development Consultancy
What is an API Gateway
An API Gateway is a service that acts as a single entry point for all API consumers. It manages request routing to the corresponding backend services, enforces authentication and authorization policies, controls usage limits (rate limiting), and can transform requests and responses between different formats. It is a key component in microservices architectures, where multiple services need to be exposed through a unified interface.
How It Works
When a client sends an HTTP request, the API Gateway intercepts it before it reaches the backend. First, it verifies authentication (JWT tokens, API keys, or OAuth). Then it applies rate limiting policies to protect services from overload. Next, it routes the request to the correct backend service based on the URL, HTTP method, and parameters. The gateway can transform the request (add headers, modify body format) and also the response before returning it to the client. Services like Amazon API Gateway, Kong, and Nginx act as managed or self-hosted gateways.
Why It Matters
Without an API Gateway, each microservice would need to implement its own authentication, rate limiting, and logging, duplicating logic and increasing the vulnerability surface. The gateway centralizes these cross-cutting concerns at a single point, simplifying security and maintenance. For teams operating multiple services, a well-configured gateway reduces coupling between services and facilitates changes like API versioning, gradual migrations, and canary deployments without modifying backend code.
Practical Example
A fintech with 12 microservices deploys Amazon API Gateway as a single entry point. All mobile app requests pass through the gateway, which validates JWT tokens, applies a limit of 100 requests per minute per user, and routes each endpoint to the correct service. When the team needs to migrate the payments service to a new version, they configure a canary deployment at the gateway: 10% of traffic goes to the new version while 90% remains on the stable version.