Proxying Expo Web Requests Through Nginx

When You Need a Proxy

Local iOS/Android clients can reach https://127.0.0.1 APIs directly, but the web bundle hits the browser CORS wall. Rather than rewriting every fetch call, tunnel the requests through Metro so they inherit the same cookies and headers your proxy provides.

Install Dependencies

Add http-proxy-middleware to your Expo workspace:

yarn add -D http-proxy-middleware

Add enhanceMiddleware

Modify metro.config.js to point the proxy to your local nginx instance.

// metro.config.js
const { getDefaultConfig } = require("expo/metro-config");
const { createProxyMiddleware } = require("http-proxy-middleware");
const connect = require("connect");

const defaultConfig = getDefaultConfig(__dirname);

module.exports = {
  ...defaultConfig,

  server: {
    ...defaultConfig.server,
    enhanceMiddleware(middleware) {
      const app = connect();

      app.use(middleware);

      app.use(
        "/api",
        createProxyMiddleware({
          target: "https://127.0.0.1:8443/api",
          changeOrigin: false,
          secure: false
        })
      );

      app.use(
        "/auth",
        createProxyMiddleware({
          target: "https://127.0.0.1:8443/auth",
          changeOrigin: false,
          secure: false
        })
      );

      return app;
    }
  }
};

Key points:

• Order matters: call app.use(middleware) first so Metro can serve bundles before the proxy runs.
• SSL to localhost: secure: false lets you hit self-signed local certs.
• One place for routes: map each upstream prefix (/api, /neo, etc.) once instead of touching client code.

Testing the Proxy

1. Start your reverse proxy (Nginx, Traefik, Caddy) on 8443 or any port.
2. Run npx expo start --web and confirm network requests flow through Metro to the proxy.
3. Switch back to --ios / --android: native builds ignore enhanceMiddleware and continue hitting upstream services directly.

Because Metro only wraps the web dev server, you don’t need environment-specific fetch logic, native builds stay blissfully unaware of the proxy.