Creating an API Gateway using Node.js and Express.js

Creating an API Gateway using Node.js and Express.js involves setting up a central service that routes and manages requests to multiple backend services. Below is a step-by-step guide to building a basic API Gateway.

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1. Install Dependencies

First, create a new Node.js project and install the required packages:

mkdir api-gateway && cd api-gateway
npm init -y
npm install express http-proxy-middleware dotenv cors

• express: Web framework for Node.js
• http-proxy-middleware: For forwarding requests to microservices
• dotenv: For managing environment variables
• cors: To enable cross-origin requests

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2. Project Structure

api-gateway/
│── .env
│── server.js
│── routes/
│   ├── authRoutes.js
│   ├── userRoutes.js
│   ├── productRoutes.js

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3. Configure .env

Create a .env file to store microservice URLs:

PORT=5000
AUTH_SERVICE_URL=http://localhost:4001
USER_SERVICE_URL=http://localhost:4002
PRODUCT_SERVICE_URL=http://localhost:4003

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4. Create server.js

Set up the Express.js server and define API gateway logic:

require("dotenv").config();
const express = require("express");
const cors = require("cors");

const app = express();
app.use(cors());
app.use(express.json());

// Import route handlers
const authRoutes = require("./routes/authRoutes");
const userRoutes = require("./routes/userRoutes");
const productRoutes = require("./routes/productRoutes");

// Use routes
app.use("/auth", authRoutes);
app.use("/users", userRoutes);
app.use("/products", productRoutes);

// Start server
const PORT = process.env.PORT || 5000;
app.listen(PORT, () => {
  console.log(`API Gateway running on port ${PORT}`);
});

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5. Create Route Handlers

Each route will act as a proxy to the corresponding microservice.

routes/authRoutes.js

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

const router = express.Router();

router.use(
  "/",
  createProxyMiddleware({
    target: process.env.AUTH_SERVICE_URL,
    changeOrigin: true,
    pathRewrite: { "^/auth": "" }, // Removes `/auth` prefix
  })
);

module.exports = router;

routes/userRoutes.js

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

const router = express.Router();

router.use(
  "/",
  createProxyMiddleware({
    target: process.env.USER_SERVICE_URL,
    changeOrigin: true,
    pathRewrite: { "^/users": "" },
  })
);

module.exports = router;

routes/productRoutes.js

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

const router = express.Router();

router.use(
  "/",
  createProxyMiddleware({
    target: process.env.PRODUCT_SERVICE_URL,
    changeOrigin: true,
    pathRewrite: { "^/products": "" },
  })
);

module.exports = router;

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6. Start the API Gateway

Run the gateway:

node server.js

Your API Gateway will forward requests:

• /auth/* → Auth Microservice
• /users/* → User Microservice
• /products/* → Product Microservice

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7. Example Microservices

To test, you can create simple microservices:

Auth Service (server-auth.js)

const express = require("express");
const app = express();
app.use(express.json());

app.get("/", (req, res) => res.send("Auth Service"));

app.listen(4001, () => console.log("Auth Service running on port 4001"));

Run it:

node server-auth.js

Similarly, create User Service and Product Service with ports 4002 and 4003.

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8. Conclusion

You now have a working API Gateway that:

• Routes requests to different services
• Hides microservice details from clients
• Centralizes authentication, logging, and request handling