How do you implement a custom API gateway in Node.js?

Question

Accepted Answer

**API gateway** — single entry point for multiple services.

```javascript
const express = require("express");
const httpProxy = require("http-proxy");

const proxy = httpProxy.createProxyServer({});

const routes = {
    "/api/users": "http://user-service:3001",
    "/api/orders": "http://order-service:3002",
    "/api/products": "http://product-service:3003",
};

const app = express();

// Authentication middleware
app.use(async (req, res, next) => {
    const token = req.headers.authorization?.split(" ")[1];
    if (token) {
        try {
            req.user = jwt.verify(token, SECRET);
        } catch (err) {
            return res.status(401).json({ error: "Invalid token" });
        }
    }
    next();
});

// Rate limiting
app.use(rateLimiter);

// Route to services
Object.entries(routes).forEach(([path, target]) => {
    app.use(path, (req, res) => {
        proxy.web(req, res, { target }, (err) => {
            res.status(502).json({ error: "Service unavailable" });
        });
    });
});

// Health check
app.get("/health", (req, res) => res.json({ status: "ok" }));

app.listen(80);
```

Node.js: How do you implement a custom API gateway in Node.js?