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.
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.