API Proxies (API Gateway as a Proxy)
What is an API Proxy
An API proxy (API Gateway) is an intermediary server that receives API requests from clients, processes them, and forwards them to backend services. Unlike regular HTTP proxies, an API Gateway specializes in managing API traffic: routing, authentication, rate limiting, transformation, and monitoring.
An API Gateway is a key component of microservice architecture and an important tool for securely exposing APIs to external consumers.
Roles of an API Proxy
1. Single Entry Point
Clients access a single address (api.example.com), and the gateway routes requests to the appropriate microservices:
- api.example.com/users → user-service
- api.example.com/orders → order-service
- api.example.com/products → product-service
2. Authentication and Authorization
The gateway verifies API keys, JWT tokens, and OAuth credentials before the request reaches the backend. This offloads the microservices.
3. Rate Limiting
Limiting the number of requests from a single client/IP within a time period. Protection against abuse and overload.
4. Request Transformation
Modification of headers, parameters, and request/response bodies. For example, converting XML to JSON for legacy services.
5. Caching
Caching API responses to reduce backend load and speed up responses.
6. Monitoring and Logging
Collecting metrics for each API endpoint: request count, latency, error rate.
API Gateway in the Context of Proxies
Differences from a Regular Reverse Proxy
| Parameter | Reverse Proxy (Nginx) | API Gateway |
|---|---|---|
| Focus | General-purpose HTTP traffic | API-specific traffic |
| Routing | By URL/Host | By API path, version, headers |
| Auth | Basic | OAuth, JWT, API keys, HMAC |
| Rate Limiting | Simple (per IP) | Advanced (per user, per plan) |
| Transformation | Minimal | Full (JSON/XML, protocol) |
| Versioning | No | /v1/, /v2/ routing |
| Developer Portal | No | Documentation, keys, monitoring |
API Gateway as a Proxy for External APIs
In addition to acting as a frontend gateway for its own services, an API proxy can be used to access external APIs:
- Aggregation — combining requests to multiple APIs into one
- Bypassing rate limits — distributing requests through an IP pool
- Caching — reducing the number of actual requests to the API
- Failover — switching between API providers
Popular API Gateway Solutions
Open Source
| Solution | Language | Features |
|---|---|---|
| Kong | Lua/Go | Most popular, plugin-based architecture |
| Tyk | Go | Built-in analytics and portal |
| KrakenD | Go | Ultra-fast, stateless |
| APISIX | Lua | Apache Foundation, dynamic routing |
| Gravitee | Java | Event-native, policy-based |
Cloud-based
| Solution | Provider | Features |
|---|---|---|
| AWS API Gateway | Amazon | Lambda integration, fully managed |
| Azure API Management | Microsoft | Developer portal, comprehensive platform |
| Google Cloud Endpoints | gRPC-native, Cloud Run integration | |
| Cloudflare API Shield | Cloudflare | DDoS protection, edge deployment |
API Proxy Usage Patterns
API Composition
The gateway combines responses from multiple microservices into a single response for the client.
Backend for Frontend (BFF)
Separate API Gateways for different clients (mobile app, web, IoT). Each is optimized for its specific client type.
API Versioning
Routing requests to different backend versions:
- /api/v1/users → old service
- /api/v2/users → new service
Circuit Breaker
Automatic disabling of a problematic backend when an error threshold is exceeded. Requests return a fallback response.
Request Shadowing
Duplicating traffic to a test backend for load testing without impacting production.
API Proxies for Bypassing Limitations
Proxying Paid APIs
Creating a proxy in front of a paid API for:
- Adding caching (cost reduction)
- Monitoring usage
- Fallback to an alternative API
- Client-side rate limiting
Bypassing CORS
An API proxy on your domain resolves CORS issues when accessing external APIs from a browser.
Protocol Transformation
Conversion between REST, GraphQL, gRPC, SOAP via an API Gateway. The client communicates using one protocol, while the backend uses another.
API Gateway Security
Key Measures
- TLS termination — HTTPS at the entry point
- Input validation — checking request parameters
- IP whitelisting — restricting access by IP
- JWT validation — token verification
- Request size limiting — limiting the size of requests
- SQL injection protection — filtering malicious requests
WAF Integration
An API Gateway is often integrated with a Web Application Firewall for additional protection against attacks.
Conclusion
API proxies and API Gateways are specialized types of proxies for managing API traffic. They ensure API security, scalability, and observability. In a microservice architecture, an API Gateway is an indispensable component, and in the context of working with external APIs, it is a powerful tool for optimization and control.