Yup, this is the way to go. You don’t need a GenServer though, a Task would suffice. And you want to pass worker(Test.Starter, [], restart: :transient) so it is not restarted right after it terminates.

I don’t quite understand your problem, but why can’t you just put a genserver at the end of the children list, which will start all your accounts and terminate? Is there really a need for genstage?

application.ex

defmodule Test.Application do
  use Application

  def start(_type, _args) do
    import Supervisor.Spec, warn: false

    children = [
      supervisor(Registry, [:unique, Test.Registry]),
      supervisor(Test.Account.Supervisor, []),
      worker(Test.Account.Starter, [], restart: :transient)
    ]

    opts = [strategy: :one_for_one, name: Test.Supervisor]
    Supervisor.start_link(children, opts)
  end
end

account/supervisor.ex

defmodule Test.Account.Supervisor do
  use Supervisor

  def start_link do
    Supervisor.start_link(__MODULE__, nil, name: __MODULE__)
  end

  def start_child(account) do
    Supervisor.start_child(__MODULE__, [account])
  end

  def init(_) do
    children = [
      worker(Test.Account, [])
    ]

    supervise(children, strategy: :simple_one_for_one)
  end
end

account/starter.ex

defmodule Test.Starter do
  use GenServer

  def start_link do
    GenServer.start_link(__MODULE__, nil)
  end

  def init(_) do
    send(self(), :start_children)
    {:ok, nil}
  end

  def handle_info(:start_children, _) do
    accounts = [:a, :b, :c]
    Enum.each(accounts, fn account ->
      Test.Account.Supervisor.start_child(account)
    end)
    {:stop, "iz kil"}
  end
end

Anyway, it’s just a suggestion. I also think there is a simpler way.

@idi527 you’re right - it should be GenServer there.

Thanks a lot, folks!