API Gateways

In a microservices architecture with dozens of backend services, should the client (mobile app or web browser) communicate directly with each service? If a single page requires data from the User Service, Product Service, and Recommendation Service, the client would need to make three separate HTTP requests to three different URLs. This is inefficient and exposes internal service details.

An API Gateway solves this by acting as a single entry point for all client requests.

1. How It Works

The API Gateway sits between the client and the backend microservices. The client sends all requests to one URL (the gateway). The gateway routes each request to the appropriate backend service, aggregates the responses if needed, and returns a single unified response to the client.

2. Core Responsibilities

• Request Routing: Routes /api/users/* to the User Service, /api/orders/* to the Order Service, etc.
• Authentication & Authorization: Verifies JWT tokens or API keys at the gateway level, so individual services don't need to implement auth logic.
• Rate Limiting: Protects backend services from abuse by limiting the number of requests a client can make per minute.
• Response Aggregation: A single client request to /api/dashboard might internally require data from 5 different microservices. The gateway fetches all 5 in parallel and returns a single combined response.
• Protocol Translation: The client communicates via REST/HTTP, while internal services might use gRPC. The gateway translates between protocols.
• SSL Termination: Handles HTTPS decryption, reducing the cryptographic load on backend services.
• Caching: Can cache frequently requested responses to reduce backend load.
• Logging & Monitoring: Centralizes request logging and metrics collection.

3. Popular API Gateways

• Kong: Open-source, built on Nginx. Highly extensible with plugins.
• AWS API Gateway: Fully managed service from AWS. Seamlessly integrates with Lambda for serverless architectures.
• Nginx: While primarily a reverse proxy, Nginx can be configured as a lightweight API gateway.
• Spring Cloud Gateway: Popular in the Java/Spring Boot ecosystem.
• Traefik: Cloud-native, integrates natively with Docker and Kubernetes.

4. Backend for Frontend (BFF) Pattern

Different clients (mobile app, web browser, smart TV) often have very different data requirements. A mobile app on a slow 4G connection needs a minimal, compressed response. A desktop web app needs a full, rich response.

The BFF Pattern creates a separate API Gateway for each client type. The Mobile BFF gateway returns minimal payloads, while the Web BFF gateway returns full payloads. Each BFF is optimized for its specific client.