API Gateway in Microservices Architecture

Introduction

In a Microservices architecture, you might have dozens of different Express servers running on different ports or subdomains. If a client app (like a React frontend or a mobile app) needs to talk to your backend, it would be a nightmare to hardcode 50 different URLs into the client.

An API Gateway acts as a single entry point (a reverse proxy) for all client requests. It receives the request, routes it to the appropriate internal microservice, and then returns the response back to the client.

Building an API Gateway with Express

You can build a fast API Gateway right in Express using the http-proxy-middleware package.

npm install express http-proxy-middleware

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

const app = express();

// Route all /users requests to the User Microservice running on port 3001
app.use('/users', createProxyMiddleware({ 
  target: 'http://localhost:3001', 
  changeOrigin: true 
}));

// Route all /orders requests to the Order Microservice running on port 3002
app.use('/orders', createProxyMiddleware({ 
  target: 'http://localhost:3002', 
  changeOrigin: true 
}));

app.listen(3000, () => {
  console.log('API Gateway is running on port 3000');
});

Gateway Responsibilities

Beyond just routing, an API Gateway is the perfect place to implement global security and performance logic:

1. Authentication: Verify JWT tokens at the gateway before routing to internal services.
2. Rate Limiting: Protect your backend from DDoS attacks by throttling requests at the gateway.
3. Caching: Cache frequent responses to reduce the load on your microservices.

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