Creating a lot of actors and messaging for the business logic of your application is considered an anti-pattern in Elixir, and a typical novice mistake. Applications in Elixir are structured using functions that are in modules that call other functions in other modules. Yes you can use OTP applications to isolate dependencies but none of this is done with the intent to more easily break up your app into a bunch of micro-services.
Which is a distinct feature made for breaking up the logic of your applications into smaller, domain bounded libraries. Umbrella apps are for the most part like regular libraries, just internal to the project which let's you do neat things like share config and deployment across them.
They don't require interacting with OTP functionality unless you make them that way and I think the OP was crossing some wires there.
No, you do not even need OTP functionality on the child project, that's my point. Not everything uses OTP.
Edit: We may be talking past each other, from Sasa Juric:
"It’s worth noting that poison is a simple OTP app that doesn’t start any process. Such applications are called library applications." Which is what I'm thinking of. He also says "Finally, it’s worth mentioning that any project you build will mix will generate an OTP app."
I was mainly talking about you don't have to use anything like GenServer or other OTP functionality with the split out app so they're more like the library application but that is still in fact an OTP application even if you're not using any of the downstream OTP features.
Each separate child project is still an OTP application, even if you do not use "OTP" features in them. OTP app is just the term for that artifact, similar to assembly or archive in other languages but it is not only terminology, each one will have `start` called when the VM starts, even if they don't spawn any servers.
