Module Federation Workshop

by @alex_lobera

We are hiring

Do you want to join Hopin and work on cutting-edge microfrontends? See open roles here.

Learning objectives

• Configure Webpack Module Federation
• Define and use explict boundaries between independent microfrontends
• Apply different routings between independent microfrontends
• Implement framework agnostic communication between microfrontends
• Identify pros and cons of microfrontends

Teaching method

1. ⬆️ Discovery ⬇️ Instruction
2. Learn by coding (and explaining things to your peers)
3. The exercise is meant to help you think and build a mental model. You are not meant to know how to do everything the exercise asks you to do.

More about our teaching method here.

Prerequisites

You need to be comfortable writing JavaScript, HTML, and React to do this exercise. Some experience with Nextjs and Webpack will be helpful but not required.

Getting started

git clone [email protected]:hopin-team/module-federation-workshop.git
cd module-federation-workshop
yarn
yarn start

Part 1: Plain JavaScript

🥑 Before JS exercise 1

A) ⚠️ Disclaimer, this is not meant to be a Webpack workshop.

B) Trainer explains briefly the two apps we have chat and host and how they are set up:

• chat/package.json scripts: "start": "webpack serve"
• How does HtmlWebpackPlugin work?
• Explain chat/src/index.js: const root = document.getElementById("root-chat");. Idem host app.

C) Trainer demo chat here http://localhost:8888/ and host here http://localhost:8887/

D) Our goal is to easily and efficiently share chat within host. We'll do that by adding ModuleFederationPlugin to chat. Trainer explains steps:

 new ModuleFederationPlugin({
    name: "chat",
    filename: "remoteEntry.js",
    exposes: {
        "./App": "./src/index.js",
    },
}),

E) Now we could import ChatApp from "chat/App" from a remote app. Trainer explains scope vs module.

🤸‍♀️ JS exercise 1

Your turn:

1- Add Module Federation to your chat.

2- Go to http://localhost:8888/ and try to identify in the network tab where txtgen is being downloaded.

3- Add Module Federation to your host. Hint, instead of defining the exposes key in ModuleFederationPlugin you must define:

// no need to interpolate the template literals, just hardcode the string
// the template literal is just to hint you the value
remotes: {
  chat: `${scope}@{remoteUrl}/${filename}`;
}

4- import the remote chat module App in host/src/index.js

🚨 Heads up 1. Even if you define the host/webpack.config.js and the import correctly you should still get this error Uncaught TypeError: Cannot read property 'call' of undefined in http://localhost:8887/. There is a non trivial issue, do you identify it? Hint, we need do add some async boundary somewhere so webpack has time to resolve the import.

🚨 Heads up 2. When you fix the previous error you'll get a new one Uncaught (in promise) TypeError: Cannot read property 'append' of null. How do you fix it? Hint: you need to add something in host/public/index.html to append the chat.

🥑 Before JS exercise 2

A) Everyone goes to the root directory of the project and:

• Stop Webpack
• Run git checkout exercise-2 && yarn && yarn start

B) Show trainees http://localhost:8888/ network tab and where txtgen is. Why is in a separate text? src/chat/webpack.config.js shared key.

C) In chat we also had to add src/bootstrap.js and import it async in src/index.js. Why do we have to do that if we don't import any remote module in chat? Hint, replace import("./bootstrap"); with import "./bootstrap"; in chat/src/index.js, navigate to http://localhost:8888/ and look at the console tab on the browser.

🤸‍♀️ JS Exercise 2

1- Add txtgen as a shared package in sessions. Make sure that http://localhost:8886/ works. Hint: add an async boundary in the entry point.

2- Why do you think it's useful in our case to add txtgen as a shared package to both sessions and chat? Hint, go to http://localhost:8887/ and look at the network tab.

3- What do you think will happen if sessions uses txtgen version 1 and txtgen version 2?

🥑 Before JS exercise 3

Well done! you've built a good Module Federation foundation. Now it's time to create better boundaries between chat, sessions, and host. We'll use the same branch.

Trainer:

A) Rename id=”root-chat” to id=”root-chat-dev” in chat/public/index.html.

B) Create a mount function in chat/src/bootstrap.js. Pass to it the DOM element to which we want to insert the content. If process.env.NODE_ENV === "development" and we found root-chat-dev then the call mount.

C) Add export default mount in chat/src/bootstrap.js

D) In chat/webpack.config.js replace:

exposes: {
    "./App": "./src/index.js",
},

with

exposes: {
    "./App": "./src/bootstrap.js",
},

🤸‍♀️ JS exercise 3

1- Everyone goes to the root directory of the project and:

• Stop Webpack
• Run git checkout exercise-3 && yarn && yarn start

2- Create a mount function in sessions/src/bootstrap and import it in host similiarly to what we just did in chat.

🏋️‍♀️ Bonus JS exercise 3

3- If the host was a React app and we wanted to mount sessions inside the host component tree, how would you invoke mount(el) in the host? Hint: you need a reference to a DOM element.

Part 2: React

🥑 Before React exercise 1

A) (Only trainer) run git checkout react && yarn && yarn start

B) Demo http://localhost:8887 and walk through code chat/src/bootstrap.js and chat/src/components/App.jsx (same for sessions and reception).

C) Comment out <div id="root-chat"></div> in src/host/public/index.html

D) In host/src/components create component ChatApp. Mount reception in a div rendered by React in ChatApp.

E) Render ChatApp component in host/src/components/App.jsx. Remove mountChat from host/src/bootstrap.js

🤸‍♀️ React exercise 1

1- (Everyone) run git checkout react-exercise-1 && yarn && yarn start

2- Create the SesssionsApp component in host/src/components similarly to the previous ChatApp.

3- Render SessionsApp in host/src/components/App.jsx.

4- Go to http://localhost:8887 and check the network tab.

• A) How many instances of React does it download?
• B) How many instances of React DOM does it download?
• C) How many instances of React Router does it download?
• D) Can you fix it so it only downloads 1 instance of each? Hint: Are you going to manually share dependencies every time you update package.json? What if you import package.json and use it in webpack.config.js?

🏋️‍♀️ Bonus React exercise 1

5- Create ReceptionApp and render it in host/src/components/App.jsx. Can you abstract out some code instead of copy & pasting from host/src/components/ChatApp?

6- Can we export reception/src/components/Schedule.jsx in the Reception ModuleFederationPlugin exposes property? Would it make sense to do that?

🥑 Before React exercise 2

We are going to add some soft navigation (no full page reload) between the host and the remotes.

⚠️ Everyone run git checkout react-exercise-2 && yarn && yarn start

Navigation from host to remote:

A) If we navigate to http://localhost:8887 and click "Reception" on the menu the content of the page doesn't change. If we reload the page from http://localhost:8887/reception it show the reception component. Let's fix this.

B) In reception/src/bootstrap.js create a history object in mount using createMemoryHistory(); from the package history and pass it to <App history={history}/> in ReactDOM.render.

C) Replace BrowserRouter with Router in reception/src/components/App and pass the prop history to <Router history={history}>.

D) In the mount function in reception/src/bootstrap.js return the following:

return {
  onHostNavigate: (pathname) => {
    history.push(pathname);
  },
};

E) In host/src/components/MountMF destructure onHostNavigate from mount( and return history.listen((e) => onHostNavigate(e.pathname));. Use useHistory to get the history object in MountMF.

🙌 At this point if we click on "Reception" in http://localhost:8887 it should work.

🙋 Any questions?

⚠️ Avoid infinite loops in the future. In reception/src/bootstrap.js add:

onHostNavigate: (nextPathname) => {
    const { pathname } = history.location;
    if (nextPathname !== pathname) history.push(nextPathname);
},

Navigation from remote to host

Now if reload the page in http://localhost:8887/reception it doesn't work.

A) In host/src/components/MountMF we pass a second argument { onNavigate } to the mount function. Now we pass a callback (onNavigate) that the remote will invoke when it changes a route. onNavigate will update the host history if the pathname is different:

onNavigate: (nextPathname) => {
    const { pathname } = history.location;
    if (pathname != nextPathname) history.push(nextPathname);
},

B) Destructure onNavigate from the mount 2nd argument (default = {}) in reception/src/bootstrap.js. If onNavigate then add a listener to history that invokes (e) => onNavigate(e.pathname)

🤸‍♀️ React exercise 2

1- Implement navigation between host and reception and reception and host as we just did. You'll know it works because you'll be able to navigate to reception by clicking on "Reception" on the navigation bar. Once in reception you'll be able to navigate to sessions by clicking on "Session 123"

2- Once you implement the previous point full page reloads won't work anymore. When we reload http://localhost:8887/reception we see now the home page instead of reception. Same thing happens in http://localhost:8887/sessions. Can you fix that? Hint: get the pathname in the host, pass it to mount and then push it to history before calling ReactDOM.render.

3- Display the chat app inside Session.jsx component above the video.

🏋️‍♀️ Bonus React exercise 2

4- If you navigate to http://localhost:8885/sessions or http://localhost:8886/reception you'll see that the remotes don't work in isolation anymore. How can you fix that? Hint, reception and sessions should not be rendered with memory history when they are not mounted by the host. What other history have we used?

5- Open the React dev tools and select the "Components" tab. In the home page (http://localhost:8887) you'll see that there are 3 React apps. In the home page we don't display sessions nor reception, why should we mount them? How would you mount only one React app on http://localhost:8887 ?

Part 3: Nextjs

🥑 Before Nextjs exercise

Nextjs current version (11.0.0) doesn't fully support Module Federation (oh 😞). The reason being Nextjs does not have an async boundary for Webpack to resolve modules in the shared scope. When using dynamic from "next/dynamic" shared packages, such as React, are downloaded more than once.

The workaround is to load the remote containers dynamically without SSR.

A) Run git checkout nextjs && yarn && yarn start

B) Let me walk you through this code src/nextjs/components/LoadNextMF. ⚠️ Notice we've added an unmount function to chat/src/bootstrap.js.

C) Mount chat in nextjs/pages/index.js using src/nextjs/components/LoadNextMF

D) How can we mount chat if there is no remotes in nextjs/next.config.js?

🤸‍♀️ Nextjs exercise

1- Everyone goes to the root directory of the project and:

• Stop Webpack
• Run git checkout nextjs-exercise-1 && yarn && yarn start

2- In http://localhost:3001/reception how many copies of React do we download? Can you find where we are downloading React in the networking tab?

3- We have not implemented any host to remote navigation nor the other way around. There is neither onHostNavigate nor onNavigate callbacks in host/src/components/LoadNextMF.jsx. Why can we click on "Reception" in the navigation bar in http://localhost:3001/ and navigate to http://localhost:3001/reception?

4- In http://localhost:3001/reception if you click on "Go to Expo 1" in the footer the expo page 1 is not loaded. Can you fix it? Hint, you'll need to use useRouter from next/router to push a pathname in LoadNextMF.jsx. Tip: pass { shallow: true } when pushing a route since we only need client-side navigation.

5- If you click on "Expo" and "Expo 1" in the navigation bar one of the two pages is not going to work. Can you fix that? You need to implement router listeners to navigate from host to remote. ⚠️ Tip: You can use this routeChangeStart event to implement a listener. Pro-tip: don't forget to cleanup listeners with router.events.off if you add any listener.

6- Do you think we should use the rest operator in nextjs/components/LoadNextMF.jsx and then spread it in MountMF and mount? Or is it better to explicitly pass each argument as we currently do? Which approach is more future-proofed? Snippet of the proposed change:

export default function LoadNextMF({
  url,
  scope,
  module,
  errorComponent: ErrorComponent = () => "There was an error",
  loadingComponent: LoadingComponent = () => "...",
  ...rest // 👈
}) {
  // some code
}

//                           👇
function MountMF({ mount, ...rest }) {
  const ref = useRef();

  useEffect(() => {
    const { unmount } = mount(ref.current, {
      // some arguments
      ...rest, // 👈
    });

    return unmount;
  }, [
    ref.current,
    mount,
    ...Object.values(rest), // 👈
  ]);

  return <div ref={ref} />;
}

🏋️‍♀️ Bonus Nextjs exercise

7- Comment out the following line in nextjs/next.config.js:

react: {
  // eager: true,  👈 comment out this line
  requiredVersion: packageJsonDeps.react,
},

Then stop Webpack and run yarn start again. You should see this error Uncaught Error: Shared module is not available for eager consumption. What does the error mean?

8- Add chat to session. Do you need to use LoadNextMF.jsx?