Customization

API Gateway Proxy Middleware

Complete guide to implementing middleware for API Gateway Proxy. Learn how to create middleware for authentication, request transformation, logging, rate limiting, and more in your AI API infrastructure.

🔄

Middleware Overview

Middleware in API Gateway Proxy is software that sits between the client request and the backend service. It enables you to add functionality like authentication, logging, rate limiting, and request transformation without modifying your core business logic.

Request Processing Pipeline

📥
Request
→
🔐
Auth
→
🔄
Transform
→
📤
Response

Why Use Middleware?

  • Separation of Concerns: Keep business logic separate from cross-cutting concerns
  • Reusability: Use middleware across multiple routes and services
  • Testability: Test middleware independently from business logic
  • Flexibility: Add, remove, or reorder middleware without code changes
  • Performance: Efficient request processing with minimal overhead
📦

Middleware Types

Here are the most common types of middleware used in API Gateway Proxy implementations:

🔐 Authentication

Validates API keys, OAuth tokens, and JWTs before allowing requests to proceed.

app.use(authMiddleware)

📝 Logging

Records request/response details, timing, and errors for monitoring and debugging.

app.use(loggingMiddleware)

🔄 Transformation

Modifies request headers, body, or query parameters before sending to backend.

app.use(transformMiddleware)

🚦 Rate Limiting

Controls request frequency per user, IP, or API key to prevent abuse.

app.use(rateLimitMiddleware)

🛡️ Security

Adds CORS headers, CSRF protection, and input sanitization.

app.use(securityMiddleware)

📊 Monitoring

Tracks metrics like response time, error rates, and request volumes.

app.use(monitoringMiddleware)
⚙️

Implementation Guide

Creating Custom Middleware

Here's how to create and register custom middleware for your API Gateway:

// Basic middleware structure
const customMiddleware = (req, res, next) => {
    // Middleware logic here
    const startTime = Date.now();
    
    // Process request
    req.customData = { startTime };
    
    // Call next middleware
    next();
};

// Register middleware globally
app.use(customMiddleware);

// Register middleware for specific routes
app.use('/api', customMiddleware);

Middleware Chaining

You can chain multiple middleware functions to create a processing pipeline:

// Define middleware chain
const middlewareChain = [
    validateRequest,
    authenticate,
    rateLimit,
    transformRequest,
    logRequest
];

// Apply middleware chain
app.use('/api', middlewareChain);

// Error handling middleware (must be last)
const errorHandler = (err, req, res, next) => {
    console.error(err.message);
    res.status(500).json({ error: 'Internal Server Error' });
};

app.use(errorHandler);

Best Practices

  • Keep middleware functions focused and single-purpose
  • Always call next() or send a response (never both)
  • Place error-handling middleware at the end of the chain
  • Use async/await with proper error handling
  • Log middleware execution for debugging
  • Consider middleware order for performance