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⚔️ Cross micro frontends communication 📦

Luís Takahashi on October 10, 2020

In this article, I'm going to explain some ways to communicate between multiple applications and a particular way that I have chosen to use in my c...

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Florian Rappl • Oct 11 '20

Really nice article - well done!

There is, however, one problem with events: You only get notified in case of changes. Especially for your problem statement (sharing some global state) you'd be interested in the current snapshot when starting. So this assumes that all interested parties are already there when the state modifier starts submitting events. This, obviously, is in general not the case. Here, you'd end up with strange situations.

A more reliable solution would be to come up with events in both directions; i.e., one to get informed about the current snapshot (originating from interested microfrontends) and one to inform about changes to the snapshot (originating from the modifier).

One problem I see with the windowed-observable lib is that it hides what it changes on window. Sure, now every microfrontend can embed this and presumably it still works (if more or less compatible versions are used) but what if somebody tries to use __shared__ for other purposes.

Thanks again!

Victor A. Barzana • Oct 14 '20

I was gonna say this but you arrived first, good point 😉 Well, you can always come up with an unique name and document it in your overall app architecture so that no one messes up with the shared thingy. Maybe this could even be configurable in your build process as an environment variable with the build number or what not. About having a snapshot of what has happened when your micro rendered is a must, so others can track/react to already triggered events.
This was really a nice article to read. Looking forward to more of your content.

Florian Rappl • Oct 15 '20

Unfortunately it's not so easy. The name has to be known by the microfrontends which are build and deployed independently.

Luís Takahashi • Oct 19 '20

Hum... to solve it those keys/namespaces could be wrapped in another package which exposes only the communication API, and every micro-frontend uses this API

Luís Takahashi • Oct 19 '20

@vbarzana This kind of comment made my day, I'll try to create more content for sure!

Luís Takahashi • Oct 11 '20

I'm glad you liked it ❤️

Yep that's the main problem using the window someone may interfere in those keys 😥

Dan Greene • Nov 11 '20

@florianrappl it's a fair point, but at a certain point don't you have to simply trust the developers and hope that you hired the right people? Also, I think documentation, training, and on-boarding at the company should help tell people that you only communicate between microfrontends through the use of the recommended library (i.e. don't touch/read directly from window, use the library instead).

Nice work @luistak

Ricardo Ruiz • Feb 23 '22

Fala Luiz.
Tudo bem?

Cara primeiro dizer que gostei muito do seu post. Muito bom mesmo...
Queria tirar umas dúvidas com você a respeito da funcionalidade de "Retrieving latest event". Estou com uma necessidade aqui no trabalho de utilizar a comunicação entre MF's e pelo que li na documentação e vi em seu video a sua lib se encaixaria muito bem, porém, acredito que não estou sabendo utilizar muito bem essa funcionalidade de obter o último evento.
Poderia trocar uma ideia?

Valeu

Chim • Oct 11 '20

This was one of the few articles worth reading in at least month. Thanks for the work you put into this. It's something I've banged my head for the past year and you just shined light on the darkest part of using this pattern. Thank you

Luís Takahashi • Oct 11 '20

This kind of comment really cheered me and pushed me to write more! I'm really glad you liked it, I held this article for a long time thinking it wasn't good enough.

I hope it helped at least a little in this matter o /

José Muñoz • Oct 11 '20

I'm going to start a migration project next month and I'm gonna use micro-frontends to approach this project, one of the things I was considering for state management is the webworker solution here! One change I would make is that I'd have a redux store on the webworker and standardize redux over both apps, great article!

Luís Takahashi • Oct 12 '20

Hi José o/

Good luck with your project!
I don't really recommend using redux as a global state in a worker, consider sharing only the essential information

If two micro frontends are frequently passing state between each other, consider merging them. The disadvantages of micro frontends are enhanced when your micro frontends are not isolated modules.

This quote from single-spa is awesome and also try to avoid "over-reduxing"

Dan Greene • Nov 11 '20

I like the window observable approach you've recommended, but I think it's important to list that it has a "con" to the approach: It misses type safety.

Sure, you can change the type in the interface from T extends any to T extends unknown and that will help a little bit. But that doesn't solve the problem that occurs when a MicroFrontend falls out of date. To phrase that as a question:

What does the observing MicroFrontend (let's call her "O") do when the publisher (let's call her MicroFrontend "P") changes the structure of the event that it's publishing?

For instance:

// in P's code on Monday
obs.publish({ foo: "bar" })
// in O's code on Tuesday
const { foo } = obs.listen();

// in P's code on Friday
obs.publish({ body: { foo: "bar" } });

What happens?

Well, MicroFrontend O is going to have a runtime error since there was no requirement to re-compile/re-deploy MicroFront O after MicroFrontend P changed it's code.

Note: Consider subscribing to me, as I'll be writing my own article on this specific problem, and I'll likely refer to yours as a starting block. Thank you for your hard work @luistak.

Luís Takahashi • Dec 15 '20

Over that problem, I would suggest creating a new abstraction that will always handle both sides and exposes a consistent API that may not change

This is the same problem as Rest api's

I've seen some folks solving this problem versioning their endpoints, so another solution would be versioning those namespaces to something like:

const observable = new Observable('v1/items');

const observable = new Observable('v2/items');

And each version would have different responses

River • Oct 13 '20

don't see the need for any of this which will add another platform dependent part into my application. Most react applications already use either mobx or redux, they are platform agnostic. I'm sure what ever library you use on Angular or Vue should expose observable or subscription api too.

Luís Takahashi • Oct 13 '20

Hi River!

The main message I was willing to pass was those types of sharing information between multiple micro-frontends, for sure your app may not need to do it what is also great!

Murali Srinivasan • Dec 14 '20

Is there any better way to securely communicate a short data between two separate Angular Applications that don't run in the browser at the same time.
For example, send some JSON data from example.com/firstAngularapp to example.com/OtherAngularApp ?

Luís Takahashi • Dec 15 '20

For sure if they're at the same domain you can use localStorage or any relevant web storage/db to sync that data

Yash Nigam • Feb 16

I have a use case in which i have to communicate from iframe to parent and vice-versa
i know how to solve it but i am unable to change the existing code base of windowed-observable
We have to replace the window object with window.top and build it.

If there is any issue with this approach we can discuss