API Gateways vs Reverse Proxies: Building Your Own API Gateway

While reverse proxies and API gateways might seem similar, they serve different purposes in modern architectures. This post explores their differences and shows how to build a custom API gateway.

Understanding the Differences

Reverse Proxy

• Simple request forwarding
• Basic load balancing
• SSL termination

API Gateway

• Advanced request routing
• Authentication/Authorization
• Rate limiting
• Request/Response transformation
• API composition
• Analytics

Building Your Own API Gateway

Core Components

interface APIGateway {
  router: Router;
  authenticator: Authenticator;
  rateLimiter: RateLimiter;
  transformer: Transformer;
  analytics: Analytics;
}

class Gateway implements APIGateway {
  async handleRequest(req: Request): Promise<Response> {
    try {
      await this.rateLimiter.checkLimit(req);
      await this.authenticator.authenticate(req);
      
      const route = this.router.findRoute(req);
      const transformedReq = await this.transformer.transformRequest(req);
      
      const response = await route.handle(transformedReq);
      const transformedRes = await this.transformer.transformResponse(response);
      
      await this.analytics.logRequest(req, transformedRes);
      return transformedRes;
    } catch (error) {
      return this.handleError(error);
    }
  }
}

Request Lifecycle

1. Rate Limiting Check
2. Authentication
3. Route Selection
4. Request Transformation
5. Backend Request
6. Response Transformation
7. Analytics
8. Response Return

Essential Features

1. Authentication/Authorization

   • JWT validation
   • API key management
   • OAuth integration

2. Rate Limiting

   • Per-user limits
   • Per-endpoint limits
   • Sliding windows

3. Request Routing

   • Path-based routing
   • Version management
   • Load balancing

4. Transformation

   • Request modification
   • Response modification
   • Error handling

Considerations

1. Performance

   • Caching strategies
   • Connection pooling
   • Efficient routing

2. Scalability

   • Horizontal scaling
   • State management
   • Distributed rate limiting

3. Monitoring

   • Metrics collection
   • Error tracking
   • Performance monitoring

Conclusion

Building a custom API gateway gives you complete control over your API infrastructure but requires careful consideration of many factors. Start with essential features and expand based on your needs.