Tutorial: Getting Started with Webpack Module Federation and Angular

This tutorial shows how to use Webpack Module Federation together with the Angular CLI and the @angular-architects/module-federation plugin. The goal is to make a shell capable of loading a separately compiled and deployed microfrontend:

This topic is also an important part of our Angular Workshop with a focus on Architectures (100% Online, Advanced, available in English and German)

Part 1: Clone and Inspect the Starterkit

In this part you will clone the starterkit and inspect its projects.

Clone the starterkit for this tutorial:

git clone https://github.com/manfredsteyer/module-federation-plugin-example.git --branch starter

Have a look to the package.json. You should find this section:
```
"resolutions": {
  "webpack": "5.0.0"
},
```
This section makes yarn to install webpack 5 for the CLI (and for all the other libraries depending on webpack).
Move into the project directory and install the dependencies with yarn:
```
cd module-federation-plugin-example
yarn
```
You really need to install the dependencies with yarn because providing resolutions as shown above is a yarn feature.
Start the shell (ng serve shell -o) and inspect it a bit:
1. Click on the flights link. It leads to a dummy route. This route will later be used for loading the separately compiled microfrontend.
  
  Please ignore depreaction warnings. They are a temporal issue in the current CLI beta when using webpack 5.
2. Have a look to the shell's source code.
  
  Please note that the current CLI beta lacks some features when using it with webpack 5, e. g. reloading an application in debug mode (when using ng serve). Hence, you have to restart ng serve after changing a source file. This is just a temporal limitation and will be solved with one of the upcoming versions.
3. Stop the CLI (CTRL+C).
Do the same for the microfrontend. In this project, it's called mfe1 (Microfrontend 1) You can start it with ng serve mfe1 -o.

Part 2: Activate and Configure Module Federation

Now, let's activate and configure module federation:

Install @angular-architects/module-federation into the shell and into the micro frontend:
```
ng add @angular-architects/module-federation --project shell --port 5000

ng add @angular-architects/module-federation --project mfe1 --port 3000
```
This activates module federation, assigns a port for ng serve, and generates the skeleton of a module federation configuration.

Switch into the project mfe1 and open the generated configuration file projects\mfe1\webpack.config.js. It contains the module federation configuration for mfe1. Adjust it as follows:

const ModuleFederationPlugin = require("webpack/lib/container/ModuleFederationPlugin");

[...]

module.exports = {
    output: {
        uniqueName: "mfe1"
    },
    optimization: {
        // Only needed to bypass a temporary bug
        runtimeChunk: false
    },
    plugins: [
        new ModuleFederationPlugin({

            // For remotes (please adjust)
            name: "mfe1",
            filename: "remoteEntry.js",

            exposes: {
                './Module': './projects/mfe1/src/app/flights/flights.module.ts',
            },        
            shared: {
                "@angular/core": { singleton: true, strictVersion: true }, 
                "@angular/common": { singleton: true, strictVersion: true }, 
                "@angular/router": { singleton: true, strictVersion: true },
                [...]
            }
        }),
        [...]
    ],
};

This exposes the FlightsModule under the Name ./Module.. Hence, the shell can use this path to load it.

Switch into the shell project and open the file projects\shell\webpack.config.js. Adjust it as follows:

const ModuleFederationPlugin = require("webpack/lib/container/ModuleFederationPlugin");

[...]

module.exports = {
    output: {
        uniqueName: "shell"
    },
    optimization: {
        // Only needed to bypass a temporary bug
        runtimeChunk: false
    },
    plugins: [
        new ModuleFederationPlugin({
            remotes: {
                'mfe1': "mfe1@http://localhost:3000/remoteEntry.js" 
            },
            shared: {
                "@angular/core": { singleton: true, strictVersion: true }, 
                "@angular/common": { singleton: true, strictVersion: true }, 
                "@angular/router": { singleton: true, strictVersion: true },
                [...]
            }
        }),
        [...]
    ],
};

This references the separately compiled and deployed mfe1 project. There are some alternatives to configure its URL (see links at the end).

Open the shell's router config (projects\shell\src\app\app.routes.ts) and add a route loading the microfrontend:
```
{
    path: 'flights',
    loadChildren: () => import('mfe1/Module').then(m => m.FlightsModule)
},
```
Please note that the imported URL consists of the names defined in the configuration files above.
As the Url mfe1/Module does not exist at compile time, ease the TypeScript compiler by adding the following line to the file projects\shell\src\decl.d.ts:
```
declare module 'mfe1/Module';
```

Part 3: Try it out

Now, let's try it out!

Start the shell and mfe1 side by side:
```
ng serve shell -o
ng serve mfe1 -o
```
Hint: You might use two terminals for this.
After a browser window with the shell opened (http://localhost:5000), click on Flights. This should load the microfrontend into the shell:
Also, ensure yourself that the microfrontend also runs in standalone mode at http://localhost:3000:

Congratulations! You've implemented your first Module Federation project with Angular!

Part 4: Switch to Dynamic Federation

Now, let's remove the need for registering the micro frontends upfront with with shell.

Switch to your shell application and open the file webpack.config.js. Here, remove the registered remotes:

remotes: {
    // Remove this line or comment it out:
    // "mfe1": "mfe1@http://localhost:3000/remoteEntry.js",
},

Open the file app.routes.ts and use the function loadRemoteModule instead of the dynamic import statement:

import { loadRemoteModule } from '@angular-architects/module-federation';

[...]
const routes: Routes = [
    [...]
    {
        path: 'flights',
        loadChildren: () =>
            loadRemoteModule({
                remoteEntry: 'http://localhost:3000/remoteEntry.js',
                remoteName: 'mfe1',
                exposedModule: './Module'
            })
            .then(m => m.FlightsModule)
    },
    [...]
]

Restart both, the shell and the micro frontend (mfe1).
The shell should still be able to load the micro frontend. However, now it's loaded dynamically.

This was quite easy, wasn't it? However, we can improve this solution a bit. Ideally, we load the remote entry upfront before Angular bootstraps. In this early phase, Module Federation tries to determine the highest compatible versions of all dependencies. Let's assume, the shell provides version 1.0.0 of a dependency (specifying ^1.0.0 in its package.json) and the micro frontend uses version 1.1.0 (specifying ^1.1.0 in its package.json). In this case, they would go with version 1.1.0. However, this is only possible if the remote's entry is loaded upfront.

Switch to the shell project and open the file main.ts. Adjust it as follows:

import { loadRemoteEntry } from '@angular-architects/module-federation';

Promise.all([
    loadRemoteEntry('http://localhost:3000/remoteEntry.js', 'mfe1')
])
.catch(err => console.error('Error loading remote entries', err))
.then(() => import('./bootstrap'))
.catch(err => console.error(err));

Open the file app.routes.ts and comment out (or remove) the property remoteEntry:

import { loadRemoteModule } from '@angular-architects/module-federation';

[...]
const routes: Routes = [
    [...]
    {
        path: 'flights',
        loadChildren: () =>
            loadRemoteModule({
                // remoteEntry: 'http://localhost:3000/remoteEntry.js',
                remoteName: 'mfe1',
                exposedModule: './Module'
            })
            .then(m => m.FlightsModule)
    },
    [...]
]

Restart both, the shell and the micro frontend (mfe1).
The shell should still be able to load the micro frontend.

Step 5: Share a Library of Your Monorepo

Add a library to your monorepo:
```
ng g lib auth-lib
```
In your tsconfig.json in the project's root, adjust the path mapping for auth-lib so that it points to the libs entry point:
```
"auth-lib": [
 "projects/auth-lib/src/public-api.ts"
]
```
As most IDEs only read global configuration files like the tsconfig.json once, restart your IDE (Alternatively, your IDE might also provide an option for reloading these settings).

Open the shell's webpack.config.js and register the created auth-lib with the sharedMappings:

const sharedMappings = new mf.SharedMappings();
sharedMappings.register(
    path.join(__dirname, '../../tsconfig.json'),
    ['auth-lib'] // <-- Add this entry!  
);

Also open the micro frontends (mfe1) webpack.config.js and do the same.

Switch to your auth-lib project and open the file auth-lib.service.ts. Adjust it as follows:

@Injectable({
    providedIn: 'root'
})
export class AuthLibService {

    private userName: string;

    public get user(): string {
        return this.userName;
    }

    constructor() { }

    public login(userName: string, password: string): void {
        // Authentication for **honest** users TM. (c) Manfred Steyer
        this.userName = userName;
    }

}

Switch to your shell project and open its app.component.ts. Use the shared AuthLibService to login a user:

import { AuthLibService } from 'auth-lib';

@Component({
    selector: 'app-root',
    templateUrl: './app.component.html'
})
export class AppComponent {
    title = 'shell';

    constructor(private service: AuthLibService) {
        this.service.login('Max', null);
    }

}

Switch to your mfe1 project and open its flights-search.component.ts. Use the shared service to retrieve the current user's name:

export class FlightsSearchComponent {

    [...]

    user = this.service.user;

    constructor(private service: AuthLibService, [...]) { }

    [...]
}

Open this component's template(flights-search.component.html) and data bind the property user:
```
<div id="container">
    <div>{{user}}</div>
    [...]
</div>
```
Restart both, the shell and the micro frontend (mfe1).
In the shell, navigate to the micro frontend. If it shows the same user name, the library is shared.

More Details on Module Federation

Have a look at this article series about Module Federation

Blog

Tutorial: Getting Started with Webpack Module Federation and Angular

Manfred Steyer

Part 1: Clone and Inspect the Starterkit

Part 2: Activate and Configure Module Federation

Part 3: Try it out

Part 4: Switch to Dynamic Federation

Step 5: Share a Library of Your Monorepo

More Details on Module Federation

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