Blog Posts - September 2018

Micro Front Ends — Doing it Angular Style Part 2

Micro Front Ends — Doing it Angular Style Part 2

In the previous part, I talked about the motivations for moving towards an MFE solution and some of the criteria for a solution to be relevant. In this part, Ill get into how we implemented it at Outbrain.

As I mentioned in the previous part, one of the criteria was for a solution that can integrate with our current technological echo system and require little or no changes to the applications we currently maintain.

Enter Angular Lazy Loading Feature Modules

Angular has a built-in concept of modules, which are basically declaration objects that specify all the components, directives, services and other modules that are encapsulated in a module.

imports: [CommonModule],
declarations: [ WelcomeComponent],
bootstrap: [],
entryComponents: []
export class AppB_Module {}

By specifying the module file as a Webpack entry point, this provided us with the ability to bundle up the entire Angular module, including css, and html as a single standalone js file.

entry: {
 'appB_module': './app/'

Using Angular lazy loading mechanism, we can dynamically load this js file and bootstrap in into our current application.

const routes: Routes = [
    path: appB,
    loadChildren: '/appB/appB_Module#AppB_Module'

This is a big step towards our goal of separating our application into a mini application.

Moving from feature modules to mini apps

Angular feature modules along with Webpack bundling gives us the code separation we need, but this is not what we enough, since Webpack only allows us to create bundles as part of a single build process, what we want to be able to produce a separate JS bundle, that is built at a different time, from a separate code base in a separate build system that can be loaded into the application at runtime and share any common resources, such as Angular.

In order to resolve this, we had to create our own Webpack loader which is called share-loader.

Share-loader allows us to specify a list of modules that we would like to share between applications, it will bundle a given module into one of the applications js bundle, and provide a namespace in which other bundles access that modules.

Application A web pack.config:

rules: [
   test: /\.js?$/,
   use: [{
     loader: 'share-loader',
     options: {
       modules: [/@angular/, /@lodash/],
       namespace: 'container-app'

Application B webpack.json

const {Externals} = require('share-loader');
externals: [
   namespace: 'container-app',
   modules: [/@angular/, /@lodash/]
output: {
 library: 'appB',
 libraryTarget: 'umd'

In this example, we are telling Webpack to bundle angular and lodash into application A and expose it under the ‘container-app’ namespace.

In application B, we are defining that angular and lodash will not be bundled but rather be pointed to by the namespace ‘container-app’.

This way, we can share some modules across applications but maintain others that we wish not to share.

So far we have tackled several of the key’s we specified in the previous post, We now have two application that can be run independently or loaded remotely at runtime while wrapped in a js namespace and have CSS and HTML encapsulation, They can also share modules between then and encapsulate modules that shouldn’t be shared, now lets look into some of the other key’s we mentioned.

DOM encapsulation

In order to tackle CSS encapsulation we wrapped each mini-app with a generic angular component, this component uses angular CSS encapsulation feature, we have two options, we can use either emulated mode or native mode depending on the browser support we require, either way, we are sure that our CSS will not leak out.

  selector: 'ob-externals-wrapper',
  template: require('./externals-wrapper.component.pug')(),
  styleUrls: ['./externals-wrapper.component.less'],
  encapsulation: ViewEncapsulation.Native

This wrapper component also serves as a communication layer between each mini-app and the other apps. all communication is done via an event bus instance that is hosted by each wrapper instance, by using an event system we have a decoupled way to communicate data in and out, which we can easily clear when a mini application is cleared from the main application.

If we take a look at the situation we have so far, we can see that we have a solution that is very much inline with the web component concept, each mini application is wrapped by a standalone component, that encapsulates all js html and css, and all communication is done by an event system.


Since each application can also run independently we can run test suites on each one independently, this means each application owner knows when his changes have broken the application and each team is concerned mostly with their own application.

Deployment and serving

In order to provide each application with its own deployment, we created a node service for each application, each time a team created a new deployment of their application a js bundle is created that encapsulates the application, each service exposes an endpoint that returns the path to the bundle. At runtime, when a mini app is loaded into the container app, a call to the endpoint is made and the js file is loaded to the app and bootstrapped to the main application. This way each application can be built a deployed separately

Closing Notes:

Thanks for reading! I hope this article helps companies that are considering this move to realize that it is possible to do it without revolutionizing your code base.

Moving to a Micro Front End approach is a move in the right direction, as applications get bigger, velocity gets smaller.

This article shows a solution using Angular as a framework, similar solutions can be achieved using other frameworks.

Increase Your Velocity with a Safe Automatic Deployment

At Outbrain we work at a fast pace trying to combine the challenges of developing new features fast, while also maintaining our systems so that they can cope with the constant growth of traffic. We deliver many changes on a daily basis to our production and testing environments so our velocity is much affected by our DevOps tools. One of the tools we use the most is the deployment tool since every new artifact must be deployed to simulation and staging environments and pass its test before it can be deployed to production. The simulation environment is used for running E2E integration tests. These tests simulate real use cases and they involve all relevant services. The staging environment is actually a single production machine (AKA a canary machine) which receives a small portion of the traffic in production. It allows us to make sure the new version is working properly in the production environment before we deploy it to the rest of the production servers. In this session, you’ll find out how we increased velocity with a safe automatic deployment of high scale services.


Our deployment flow


The illustration above depicts the flow each code change must pass until it arrives in production.

A developer commits code changes and triggers a “build & deploy” action that creates an artifact for the requested service and deploys it to our simulators servers. Once an hour, a build in TeamCity runs the simulation tests of our services.

If the developer doesn’t want to wait for the periodic run, they need to run the simulation tests manually. Once the build passes, the developer is allowed to deploy the artifact to the staging server. At this point, we verify that the staging server behaves properly by reviewing various metrics of the server, and by checking the logs of that server.

For instance, we verify that the response time hasn’t increased and that there are no errors in the log. Once all these steps are completed, the new version is deployed to all production servers. This whole process can take 30-45 minutes.

As one can see, this process has a lot of problems:

  1. It requires many interventions of the developer.
  2. The developer either spends time waiting for actions to complete in order to trigger the next ones or they suffer from context switches which slow them down.
  3. The verification of the version in staging is done manually hence
  • It’s time-consuming.
  • There is no certainty that all the necessary tests are made.
  • It’s hard to share knowledge among team members of what the expected result of each test is.

The new automatic pipeline

Recently we have introduced a pipeline in Jenkins that automates this whole process. The pipeline allows a developer to send code changes to any environment (including production) simply by committing them into the source control while ensuring that these changes don’t break anything.

The illustration below shows all stages of our new pipeline

Aside from automating the whole process, which was relatively easy, we had to find a way to automate the manual tests of our staging environment. As mentioned, our staging servers serve real requests coming from our users.

Some of our services handle around 2M requests per minute so any bad version can affect our customers, our users, and us very quickly. Therefore we would like to be able to identify bad versions as soon as possible. To tackle this issue, our pipeline starts running health tests on our staging servers 5 minutes after the server goes up since sometimes it takes time for the servers to warm up.

The tests which are executed by TeamCity, pull a list of metrics of the staging server from our Prometheus server and verify that they meet the criteria we defined. For example, we check that the average response time is below a certain number of milliseconds. If one of these tests fail, the pipeline fails. At that point, the developer who triggered the pipeline receives a notification e-mail so that they can look into it and take the decision whether the new version is bad and revert it, or maybe the tests need some more fine-tuning and the version is okay to deploy to the rest of the servers.

The pipeline ends when the new version is deployed to production but this doesn’t necessarily mean that the version is 100% okay, although the chances that the version is not okay at this stage are low.

For the purpose of ensuring our production servers function properly, many periodic tests constantly monitor the servers and trigger alerts in case of a failure and allow us to react fast and keep our services available.


What we gained

  1. The automated deployment process ensures the quality of our deliveries and that they don’t break our production servers.
  2. Reduction of time developers spends on DevOps tasks.
  3. The decision whether a version in staging is okay is more accurate as it is based on comparable metrics and not on a subjective decision of the developer.
  4. The developer doesn’t need to remember which metrics to check for each service in order to tell whether a service functions properly.