API Gateway
Definition
An API gateway is a server that acts as a single entry point for API requests, sitting between clients and backend services. It handles cross-cutting concerns such as authentication, rate limiting, request routing, load balancing, caching, monitoring, and protocol translation -- centralizing these functions so that individual services do not need to implement them.
Why It Matters
In modern architectures with multiple backend services, each service cannot independently handle authentication, rate limiting, and monitoring. An API gateway centralizes these concerns, providing a consistent security and management layer across all APIs.
For external APIs (consumed by partners, customers, or mobile applications), the gateway enforces authentication, applies rate limits, transforms request/response formats, and provides analytics on API usage.
For internal APIs (service-to-service communication), the gateway provides service discovery, load balancing, circuit breaking, and observability.
API gateways are also critical for security. They enforce authentication at the edge, preventing unauthenticated requests from reaching backend services. They apply rate limiting to prevent abuse. They can inspect requests for malicious content and block known attack patterns.
Key Capabilities
- Authentication & Authorization -- Validate API keys, OAuth tokens, or JWT claims before routing to backends
- Rate Limiting -- Throttle requests per client, per API, or per time window
- Request Routing -- Direct requests to the appropriate backend service based on path, headers, or content
- Load Balancing -- Distribute requests across multiple service instances
- Caching -- Cache responses for frequently requested, infrequently changing data
- Monitoring & Analytics -- Track request volumes, latency, error rates, and usage patterns
How BAG Uses It
We implement API gateways as part of every platform architecture we design. For client-facing APIs, we use gateways with OAuth 2.0 authentication, per-client rate limiting, and comprehensive logging. For internal service communication, we use service mesh capabilities (Linkerd or Istio) for mTLS, load balancing, and observability.