What is an API Gateway?

What You'll Learn

• What an API Gateway is
• Key features
• Popular solutions

What is an API Gateway?

An API Gateway is a single entry point for all client requests that routes to appropriate microservices.

Key Features

• Routing - Direct requests to services
• Authentication - Centralized auth
• Rate limiting - Protect services
• Load balancing - Distribute traffic
• Caching - Reduce backend load
• Monitoring - Centralized logging

Architecture

Client → API Gateway → Service A
                    → Service B
                    → Service C

Popular Solutions

• Kong - Open source, Lua plugins
• AWS API Gateway - Managed, serverless
• NGINX - High performance
• Express Gateway - Node.js based

Simple Implementation

const express = require('express');
const { createProxyMiddleware } = require('http-proxy-middleware');

const app = express();

// Authentication middleware
app.use(authenticate);

// Rate limiting
app.use(rateLimit({ windowMs: 60000, max: 100 }));

// Route to services
app.use('/api/users', createProxyMiddleware({
  target: 'http://user-service:3001',
  changeOrigin: true,
}));

app.use('/api/orders', createProxyMiddleware({
  target: 'http://order-service:3002',
  changeOrigin: true,
}));

app.use('/api/products', createProxyMiddleware({
  target: 'http://product-service:3003',
  changeOrigin: true,
}));

app.listen(3000);

Benefits

• Single entry point simplifies client
• Centralized cross-cutting concerns
• Can transform/aggregate responses
• Easier to manage and monitor