I have an app like

stackdelivery
    ├── lib
            └── stackdelivery
                    └── application.ex
            └── stackgen
                     └── stackgen.ex
                     └── supervisor.ex
            stackdelivery.ex
    mix.exs

application.ex is

defmodule Stackdelivery.Application do
  # See http://elixir-lang.org/docs/stable/elixir/Application.html
  # for more information on OTP Applications
  @moduledoc false

  use Application
  use Supervisor

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

    # Define workers and child supervisors to be supervised
    children = [
      supervisor(Stackdelivery.StackGen.Supervisor, [])
    ]

    # See http://elixir-lang.org/docs/stable/elixir/Supervisor.html
    # for other strategies and supported options
    opts = [strategy: :one_for_one, name: Stackdelivery.StackAppSupervisor]
    Supervisor.start_link(children, opts)
  end

end

supervisor.ex is

defmodule Stackdelivery.StackGen.Supervisor do
  @moduledoc """
  Supervisor for StackGen module
  """

  use Supervisor
  alias Stackdelivery.Stack

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

  def init(_) do
    IO.puts "starting StackGen.Supervisor supervisor.."
    children = [
      worker(Stack, [])
    ]
    opts = [strategy: :simple_one_for_one, name: Stackdelivery.StackGenSupervisor]
    supervise(children, opts)
  end

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

stackgen is a simple Stacn Genserver. for brevity:

defmodule Stackdelivery.Stack do
  use GenServer

  def init(_) do
    IO.puts "Starting a New GenServer Stack" 
    {:ok, []}
  end
....

I can’t start multiple child processes using Stackdelivery.StackGen.Supervisor.shoot

The way I am thinking is how supervision tree should be is:

Application (Main Supervisor)
└── StackGen.Supervisor (Module Supervisor)
         └── Stackgen (GenServer)

Now when Application.start_link happens, how can we invoke child proceses in StackGen.Supervisor for Stackgen workers?