I’ve been writing a few applications at work in elixir/phoenix and I understand that Phoenix and Ecto utilize supervisors and processes under the hood but I’m curious as to when it’s a good idea to reach for my own supervisor tree inside of a phoenix application? My only idea would be when I need to reach for some background job processing that it would make sense to do that.
Are there any other common problems inside of a phoenix / web app that a supervisor tree and/or OTP Genservers make sense?
Yes, embrace supervision trees for any additional processes beyond the Cowboy handler and Ecto pools. Some use cases I’ve had for starting additional processes:
caching data in ETS owned by a GenServer
Task.Supervisor for non-durable async tasks
GenStage producers / consumers for interacting with external systems
Postgrex.Notifications
Only thing to watch out for is introducing bottlenecks by putting stateless business logic behind GenServer interfaces.
Your own (application and) supervision tree becomes important once you decide to build the application independent of Phoenix - i.e. Phoenix is simply used to build the web interface for your application - an approach advocated in
I use separate processes, for background processing, plus a common ephemeral store for data that gets used in multiple requests (because the data can be reconstituted by hitting an API, but I don’t want to hit that API on every request).
