Communicating between umbrella apps

I’m curious how people are communicating between their umbrella apps.

We currently have an umbrella app that has a dependency structure like this:

ProxyApp -> GraphQLService -> BusinessDomain

Each app depends on the next app as a dependency. No app can depend on another app at the same layer. So no Service app can depend on another Service app and no Domain app can depend on another Domain app. This helps keep the app maintainable and it reduces coupling.

However, there are instances where it makes sense for one app to notify another app in the same layer that something happened.

I’m curious if anyone has gone down this route with umbrella apps or maybe even something adjacent like microservices. If so, what has your experience been?

I’ve looked at event sourcing but that seems overkill for what I need. I also thought about using an AMQP service but thought I might be able to implement something using straight OTP.

Curious to hear people’s thoughts and opinions.

One thing that might definitely help here is Phoenix.PubSub, which allows apps to subscribe to and publish events.
Of course, you can also go full-blown event-sourcing, but for all ephemeral types of events, you need nor want this. :slight_smile:

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