Hey all, I’m pulling my hair out over how to properly design my supervision structure. It works right now but only because processes are restarted often enough to eventually fall in the right order.

I’m sure there’s an obvious right solution here that I just don’t see (pretty new to elixir). Anyone got an idea?

I’m building a single-user interactive app. There are four GenServers:

• The ModelManager serves as a central point to store the underlying data. (makes it easier to implement sync later) Processes can subscribe to the ModelManager and be notified in the event of changes.
• The Frontend (a TUI using the Ratatouille library) presents the UI and pushes changes to the ModelManager. It also listens to change events emitted from the ModelManager (e.g., because of sync).
• The frontend actually needs a little MsgTransformer process between itself and the ModelManager to transform the messages into a shape that Ratatouille can deal with.
• The FileSaver implements autosave by listening to change events from the ModelManager and writing them to disk.

I even made a little diagram:

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The problem I’m facing is startup: in principle it’s clear what should happen:

• The ModelManager should start first.
• Then we can start FileServer and MsgTransformer (the MsgTransformer actually belonging to the Frontend; nobody else has to know about this)
• Finally we can start the Frontend.

This order is necessary so everyone can subscribe / reference the other processes when they need to. But I have no idea how to make this happen.

Right now I’m just putting all four processes as directly supervised children under my main app tree. Some process (the frontend specifically) crash upon init because the ModelManager isn’t live yet, so it can’t subscribe. But the supervisor restarts it, so it’ll eventually be fine. — But this is definitely not a clean design right?