Host Routing

Host Routing Overview

Host Routing lets you structure Module Federation work so it stays readable, testable, and easy to scale. Instead of ad-hoc code, you follow a clear pattern that other developers can recognise immediately.

The key is to keep host routing focused and predictable. Start from the minimal example here, then layer in only the complexity your feature actually needs.

// host (webpack.config.js)
const { ModuleFederationPlugin } = require('webpack').container;

module.exports = {
  plugins: [
    new ModuleFederationPlugin({
      name: 'shell',
      remotes: {
        catalog: 'catalog@http://localhost:3001/remoteEntry.js',
      },
      shared: ['react', 'react-dom'],
    }),
  ],
};

// usage
const ProductList = React.lazy(() => import('catalog/ProductList'));

The host declares remotes by URL and lazy-loads exposed modules like any dynamic import.

Host Routing Example

new ModuleFederationPlugin({
  name: 'app',
  filename: 'remoteEntry.js',
  exposes: { './Widget': './src/Widget' },
  remotes: { other: 'other@http://host/remoteEntry.js' },
  shared: { react: { singleton: true } },
});

• Start from a minimal Host Routing example and grow it only as needed.
• Keep configuration explicit so Host Routing behaves the same in every environment.
• Name things clearly so teammates understand your Host Routing at a glance.
• Add tests around Host Routing early to lock in expected behaviour.

Module Federation Cheatsheet

Key Module Federation settings related to host routing.

How Host Routing Works in Module Federation

Host Routing builds on Module Federation's ability to load code from another independently built and deployed application at runtime. Each app can be a host, a remote, or both.

The host declares remotes by URL and lazy-loads exposed modules like any dynamic import.

• Remotes expose modules through a remoteEntry.js manifest.
• Hosts declare remotes and import exposed modules dynamically.
• Shared dependencies are deduplicated, ideally as singletons.
• Each micro frontend builds and deploys on its own schedule.

Practical Guidance for Host Routing

In production, host routing needs careful version management and graceful failure handling. Align shared dependency versions and always render a fallback when a remote cannot load.

Common Mistakes

• Copying host routing snippets without understanding what each line does.
• Skipping error handling and edge cases when wiring up host routing.
• Leaving host routing untested, so regressions slip into production.
• Over-engineering host routing before you actually need the extra flexibility.

Key Takeaways

• Host Routing is a core part of working effectively with Module Federation.
• Start small and keep host routing focused on a single responsibility.
• Apply consistent patterns so host routing scales across your project.
• Test and document host routing to keep it maintainable over time.