I have an app structuring question regarding Nerves. First I’ll generally describe my app on a high level.

I’m making a game where RFID readers will play an integral part. The game consists of many devices (different kinds of Raspberry Pi) acting as a network and synchronising game state together. There are initially three types of devices:

1. Player device: This is worn by the player and contains an RFID reader. Each player also has an RFID tag in their hand. The player device connects to the others with WiFi. If the RFID reader detects another player’s code, that player has tagged the wearing player and the wearing player’s tag will be disabled from affecting other players (by communicating this to all other players). Then that player must go to read their tag at a respawn station to reactivate their tag.
2. Respawn device: This is stationary somewhere and will connect via Ethernet most likely. When the respawn station’s RFID reader detects a tag, it should communicate to all the devices that that player’s tag is active again.
3. “Judge” that coordinates the whole game. This device should also offer a web page probably with Phoenix that can be used to set up and follow the game. Another feature could be permanent storage of game info to PostgreSQL/SQLite for example.

Now my issue is, how should I structure my code? The two first devices are similar enough, but the third would also have Phoenix and maybe other stuff, but it still needs the game coordination code that is common to all three. I know of umbrella applications but I thought they are not the solution if you only want to start part of the applications in some environments, or am I wrong?