Micro Frontend Architecture: Module Federation, Single-SPA & Beyond

Micro frontends extend the microservices pattern to the frontend — each team owns an independent slice of the UI, from database to deploy button.

Why Micro Frontends#

Monolithic Frontend                Micro Frontend
┌───────────────────────┐          ┌───────┐ ┌───────┐ ┌───────┐
│                       │          │ Team  │ │ Team  │ │ Team  │
│    One giant app      │          │   A   │ │   B   │ │   C   │
│    One repo           │    →     │ React │ │  Vue  │ │ Svelte│
│    One deploy         │          │ own   │ │ own   │ │ own   │
│    One team backlog   │          │ CI/CD │ │ CI/CD │ │ CI/CD │
│                       │          └───────┘ └───────┘ └───────┘
└───────────────────────┘              ↓         ↓         ↓
                                   ┌───────────────────────────┐
                                   │   Shell / Container App   │
                                   └───────────────────────────┘

Benefits#

• Independent deployments — team A ships without waiting for team B
• Technology freedom — each micro frontend can use a different framework
• Autonomous teams — vertical ownership from UI to API
• Isolated failures — a crash in one module does not take down the whole page
• Incremental migration — rewrite one section at a time, not the entire app

Trade-offs#

• Increased complexity — orchestration, routing, shared state
• Bundle duplication — risk of shipping React twice without careful sharing
• Consistency — harder to keep UX uniform without a shared design system
• Testing — integration tests must span multiple micro frontends

Integration Approaches#

1. Module Federation (Webpack 5 / Rspack)#

Module Federation lets separately built and deployed bundles share modules at runtime.

┌─────────────────┐     ┌─────────────────┐
│  Shell App      │     │  Checkout MFE   │
│  (host)         │ ←── │  (remote)       │
│  exposes: nav   │     │  exposes:       │
│  consumes:      │     │    CartWidget   │
│    CartWidget   │     │    CheckoutPage │
└─────────────────┘     └─────────────────┘

Host configuration (shell):

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

module.exports = {
  plugins: [
    new ModuleFederationPlugin({
      name: 'shell',
      remotes: {
        checkout: 'checkout@https://checkout.cdn.example.com/remoteEntry.js',
        catalog: 'catalog@https://catalog.cdn.example.com/remoteEntry.js'
      },
      shared: {
        react: { singleton: true, requiredVersion: '^18.0.0' },
        'react-dom': { singleton: true, requiredVersion: '^18.0.0' }
      }
    })
  ]
};

Remote configuration (checkout):

// webpack.config.js — Checkout MFE
new ModuleFederationPlugin({
  name: 'checkout',
  filename: 'remoteEntry.js',
  exposes: {
    './CartWidget': './src/CartWidget',
    './CheckoutPage': './src/CheckoutPage'
  },
  shared: {
    react: { singleton: true, requiredVersion: '^18.0.0' },
    'react-dom': { singleton: true, requiredVersion: '^18.0.0' }
  }
});

Consuming a remote module:

const CartWidget = React.lazy(() => import('checkout/CartWidget'));

function App() {
  return (
    <React.Suspense fallback="Loading cart...">
      <CartWidget />
    </React.Suspense>
  );
}

2. Single-SPA#

single-spa is a framework-agnostic orchestrator that mounts and unmounts micro frontends based on URL routes.

URL: /dashboard  → mount Dashboard MFE
URL: /settings   → mount Settings MFE
URL: /checkout   → mount Checkout MFE

Each MFE registers lifecycle hooks:
  bootstrap → mount → unmount

Registration:

import { registerApplication, start } from 'single-spa';

registerApplication({
  name: 'dashboard',
  app: () => System.import('@org/dashboard'),
  activeWhen: ['/dashboard']
});

registerApplication({
  name: 'checkout',
  app: () => System.import('@org/checkout'),
  activeWhen: ['/checkout']
});

start();

MFE lifecycle:

// dashboard/src/lifecycle.js
export function bootstrap() { /* one-time init */ }
export function mount(props) { /* render into props.domElement */ }
export function unmount(props) { /* cleanup */ }

3. Web Components#

Framework-agnostic by design. Each micro frontend ships as a custom element.

// catalog-mfe/src/index.js
class CatalogWidget extends HTMLElement {
  connectedCallback() {
    this.innerHTML = '<div id="catalog-root"></div>';
    renderCatalogApp(this.querySelector('#catalog-root'));
  }
  disconnectedCallback() {
    unmountCatalogApp(this.querySelector('#catalog-root'));
  }
}
customElements.define('catalog-widget', CatalogWidget);

Usage in the shell:

<catalog-widget></catalog-widget>
<checkout-widget cart-id="abc123"></checkout-widget>

4. Iframe Approach#

The simplest but most limited approach. Each MFE runs in a sandboxed iframe.

Pros: Complete isolation, any framework, no JS conflicts
Cons: No shared state, poor UX (scroll, navigation), SEO issues

Best suited for admin panels or third-party embeds where isolation matters more than seamless UX.

Approach Comparison#

Shared Dependencies#

Duplicating React, Vue, or large libraries across every MFE bloats the page. Strategies to avoid this:

Singleton Sharing (Module Federation)#

shared: {
  react: { singleton: true, eager: false },
  'react-dom': { singleton: true, eager: false },
  '@org/design-system': { singleton: true }
}

Import Maps (single-spa / native)#

{
  "imports": {
    "react": "https://cdn.example.com/react@18/index.js",
    "react-dom": "https://cdn.example.com/react-dom@18/index.js"
  }
}

Version Contract#

All teams agree on major version ranges for shared dependencies. A shared package.json or lockfile enforces this.

Routing#

Shell-Owned Routing#

The shell app handles top-level routes and delegates sub-routes to each MFE:

Shell routes:
  /catalog/*   → Catalog MFE (owns /catalog/product/:id, /catalog/search)
  /checkout/*  → Checkout MFE (owns /checkout/cart, /checkout/payment)
  /account/*   → Account MFE

Communication Between MFEs on Route Change#

// Custom event for cross-MFE navigation
window.dispatchEvent(new CustomEvent('navigate', {
  detail: { path: '/checkout/cart', meta: { productId: '123' } }
}));

State Sharing#

Micro frontends should be loosely coupled. Avoid a global Redux store shared across teams.

Recommended Patterns#

Custom Event Example#

// Catalog MFE — dispatch
window.dispatchEvent(new CustomEvent('add-to-cart', {
  detail: { productId: '456', quantity: 1 }
}));

// Checkout MFE — listen
window.addEventListener('add-to-cart', (e) => {
  addItemToCart(e.detail.productId, e.detail.quantity);
});

Deployment Independence#

Each micro frontend has its own CI/CD pipeline:

Team A pushes to catalog repo
  → Build catalog MFE
  → Upload to CDN (catalog.cdn.example.com/remoteEntry.js)
  → Shell fetches latest remoteEntry.js on next page load

Team B's checkout MFE is unaffected.

Versioning Strategies#

• Latest — shell always fetches the latest remoteEntry.js (simplest)
• Pinned — shell references a specific version URL (safest)
• Canary — deploy to a percentage of users first

Design System Integration#

A shared design system prevents micro frontends from looking like Frankenstein UIs.

┌─────────────────────────────┐
│   @org/design-system        │
│   (shared npm package)      │
│   Buttons, Forms, Layout,   │
│   Tokens, Typography        │
└──────────┬──────────────────┘
           │ consumed by all MFEs
   ┌───────┼───────┐
   ▼       ▼       ▼
 Shell  Catalog  Checkout

Guidelines#

• Publish the design system as a versioned npm package
• Use design tokens (colors, spacing, typography) so MFEs stay consistent
• Mark the design system as a shared singleton in Module Federation
• Run visual regression tests across all MFEs when the design system updates

Common Pitfalls#

1. Sharing too much state — tight coupling defeats the purpose of micro frontends
2. Duplicate bundles — forgetting to configure shared dependencies doubles page weight
3. No design system — each team invents its own buttons and the UI becomes inconsistent
4. Over-splitting — not every page needs to be a micro frontend; start with 2-3 boundaries
5. Ignoring performance — loading four remoteEntry.js files serially kills page load
6. No contract testing — a breaking change in one MFE silently breaks the shell

When to Use Micro Frontends#

Good Fit#

• Large organization with multiple autonomous frontend teams
• Legacy app that needs incremental rewrite
• Platform with distinct product areas (e-commerce: catalog, cart, account)
• Teams with different preferred frameworks

Bad Fit#

• Small team (under 10 developers) — the overhead is not worth it
• Simple app with few pages
• Performance-critical apps where every kilobyte matters
• Team with strong shared codebase and no autonomy issues

Quick-Start Checklist#

[ ] Define team boundaries (which team owns which page/feature)
[ ] Choose an integration approach (Module Federation recommended)
[ ] Set up a shared design system package
[ ] Configure shared dependencies as singletons
[ ] Implement shell-owned routing with delegated sub-routes
[ ] Use custom events for cross-MFE communication
[ ] Give each MFE its own CI/CD pipeline
[ ] Add integration tests that span the shell + MFEs
[ ] Monitor bundle sizes per MFE

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Explore the full architecture series on Codelit.io. This is article #348 in our growing library of software architecture and system design guides.