Host Application

Host Application Overview

Host Application is a building block you will reach for often in Module Federation. It keeps related logic together and makes your intent obvious to reviewers and future maintainers.

When you learn host application properly, you avoid the guesswork that leads to bugs and rework. The example below shows the shape you will use in most real Module Federation projects.

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

Module Federation Cheatsheet

Key Module Federation settings related to host application.

How Host Application Works in Module Federation

Host Application 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 Application

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

Common Mistakes

• Skipping error handling and edge cases when wiring up host application.
• Leaving host application untested, so regressions slip into production.
• Over-engineering host application before you actually need the extra flexibility.
• Ignoring documentation, which makes host application hard for the next developer to change.

Key Takeaways

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