There are a few ways you can do it. Personally, I would approach it this way:

One: Create a custom mix task for your background worker. This is good intro: Custom Mix Tasks · Elixir School

I would actually base this task on how phx.server task is structured. Have a look here: phoenix/lib/mix/tasks/phx.server.ex at v1.3.0-rc.2 · phoenixframework/phoenix · GitHub

so what it does is two things a) sets some configuration option to force starting web server, b) starts all applications with Mix.Tasks.Run.run and that’s it.

Two: In the newly created task, I would set different configuration option. Something like `Application.put_env :my_app, :start_background_stuff, true.

Then, I would use this environment variable in your application callback module (application.ex), and check if the value is true, and only if it is - would start the GenServer I want to be running.

Please note that if you do the above, it will work fine as long as you don’t intend to send messages to this GenServer from your Phoenix workers. It won’t work and will throw you with error that no process exists. This will be because on Heroku, background dyno will start as a separate OS process, in fact in a separate container and most likely on different hardware altogether. Since you just want to run something every 15 minutes that should not be a problem I think.

Which, however, brings me to the other point that you might want to use something like quantum instead GitHub - c-rack/quantum-elixir: Cron-like job scheduler for Elixir · GitHub . In such case, I would still implement it in a similar way - create a custom mix task, set config variable in it - and only if the variable is set - configure quantum scheduler. Otherwise (on web dynos) no scheduler would be configured.

I think @HenriMorlaye just starts mix phx.server for his web dynos. If that’s the case, then it’s quite easy because in Procfile just should specify different mix task, and the variables used would not be shell environment variables at all.

Thank you !
I tried something which seems to be working. I my Procfile I have put:

web: mix phoenix.server
worker: WORKER_APP=true mix phoenix.server

and just changed the MyApp.ex application file to add in the Supervisor the genserver if the env variable “WORKER_APP” exists, and add MyApp.Endpoint if the env variable is empty.