Evolving Web legacy systems with Microfrontends and Web Components

William Grasel

This is not a talk about easy answers and silver bullets 

We have one of the biggest Web legacy system of Brazil

It is not something always to complain about, some decisions were better than others

We have a lot of REALLY good people working hard for generations!

But it is impossible to makes the right decision every time

Some bad decisions of the past will pile up each other over the years...

Sometimes you to calm down and understand what is going on and where do we wanna go

We wanna learn with the best practices and tools in the market

But we cannot go crazy and use all the latest hype of the moment

Or it can become yet another bad decision on our history!

Welcome to Itaú's

Digital Foundation

We don't delivery software to the company final user

Our job is to test out new technologies and understand how can  they be applied

to our reality

We build tools, sdk, components to

enable and standardize

the use of new technologies

We are not the only one doing that inside Itaú, but we are a community only focusing on that

We have a big team focused on FrontEnd!

This talk is a brief of the latest things we are learning and some of the path we chose in FrontEnd Architecture

MicroFrontend: the newest and biggest hype of the moment!

What is exactly is

Microfrontend ?


  • Tool?
  • Lib?
  • Framework?
  • Hype?


is more a:


  • Concept
  • Architectural pattern

The idea seams to bring the microservices architecture to the FrontEnd world!

Simple, right?

Well, it still too vague...

But everybody is talking about it, so must be cool! Right?

Lets do some research about it!

Lets seek to the source, the origin of this term!

The first referencie the we cold find at the internet using Google Search Tools was...

Several others blog posts e small articles appeared after that

So, looks like it mature enough to use, right? Well...

Until this moment...

There is no Wikipedia page about it

There isn't any kind of Manifest page about it

There is no book about, no detailed information of implementation 

People is using the same term to talk about totally different things

Articles and talks about it seams to disagree not only in principles, but also about how to implement it

Evolution of Web Architecture

This is the CORE idea of MicroFrontend!

That's were most people agrees on!

Some other secondary points:

  • Autonomous teams
  • Independent deployment
  • Decoupled codebases
  • Be Technology Agnostic

Technology Agnostic

Lets talk about

Web Performance!

In average mobile sites takes up to 15 seconds to load!

53% of users leave websites if they doesn't load in 3 seconds!

Interactive websites in less than 5 seconds have:

  • 70% longer sessions
  • 35% less rejection rate
  • 25% more visibility in advertising

JavaScript is one of the biggest villains in Web Performance!

200kb of JPG and JS are not the same thing!

To archive the 5 seconds of interaction, 300kb of JS is the maximum acceptable for an average phone!

But we normally delivery much much more than that!

Web Performance is HARD! It is difficult to get and easy to ruin!

But it is also very important to almost any case of success on the Web!

Web Performance in the context of MicroFrontend!

Do you remember that?

Each framework takes an average of ~30kb of compressed JS alone

3 frameworks at the same page will cost up to 1/3 of your 300kb

This is completely UNACCEPTABLE if care about performance!

"But I have heard that Spotify use exactly this model"

Yes, they do, but for the desktop app, where performance is not an issue

Is there any way to have technology independence without blow up performance?

MicroFrontends at IKEA

Still not optimal, performance is gonna be even harder than normal to deal...

At least it is something it is possible to deal

So, is it worth? Does it pay its price?

Do I really need this level of technology isolation?

Autonomy and Technology Isolation

What we really want is Autonomy

Philosophical question:

Do we really need total technology isolation to be autonomous?

Well, no...

Most of the companies have technologies constrains to their context

Autonomy doesn't mean freedom to use my favorite technologies regardless of context

If you want to use MicroFrontend just as an excuse so your team use the new hype framework of the week, well...

But sometimes your context DO requires Technology Isolation

We had two scenarios where Technology Isolation were necessary

First: security components and services

With the security, Technology Isolation will ALWAYS be a requirement

Second: new features on legacy that need to start RIGHT NOW

Teams really needed better tools to introduce new features at the legacy

And they needed a way to do it without broke the legacy or with other 

But even in complete isolation, teams are required to use the same framework, languages and tools

WebComponents API from HTML5 were the perfect tool to glue up everything together

Angular Elements

We were not convinced that this model were the best solution to the long run

Long term MicroFrontend Architecture 

We wanted autonomy, but Technology Isolation has it own problems

We wanted a better way  to deal with internal and external dependencies

What is the version that Google uses of Angular?

What version of React inside Facebook?

The answer for both is: always the last one!

There is only one way to do it: Monorepo!

Almost all the big tech companies uses Monorepos!

All those companies also use MicroServices in some way

So MicroFrontend shouldn't be a problem as well

We don't intend to magically transform the whole company in a big Monorepo

But it would help to manage some new projects that may work together

What if we can reuse those MicroFrontend across different channels and apps?

We believe that Monorepo would also help with that!

Tools for scaling big Code Bases

To archive Monorepo, we can start thinking about the workspace concept



Isolated Feature Modules independent deployed and lazy loaded for one or more apps to consume!

The AngularCLI is extremely extensible and powerful!

But we would have to customize so many things to get to the point were we wanted...

Lerna is very powerful and focused on Monorepo tools!

But we would have to customize other set of items...

Extensible Dev Tools for Monorepos

Collections of tools built on top of the


for monorepos

But it also has first-class support for many frontend and backend technologies

Simple Commands

npm run dep-graph

npm run affected:build

npm run affected:test -- --parallel

We are working right now to integrate with Nx tools

But let's talk even a little far into the future...



Thanks! =)

Evolving Web legacy systems with Microfrontends and Web Components

By William Grasel

Evolving Web legacy systems with Microfrontends and Web Components

Itaú Unibanco has one of the largest and oldest internet banking of the world, it has a long old story, a story that we are not always proud to tell about. But we can't just rewrite everything from the ground up, if we want to update it we need to find a way to do it coexisting with the legacy for a long time. This is not a introductory and conceitual talk, that's a story of how are using a microfrontend architecture with the Web Component technology, how we are scaling these tools for thousands of developers working on it at the same time, and finally automatizing everything we could in the way! We hope our story can bring some hope and ideas for other companies out there to deal with their own legacy.

  • 689
Loading comments...

More from William Grasel