I’ve got an app that connects to a number of TCP sockets using Ranch.

The supervision tree looks like this:

|-------|
|  APP  |
|-------|
   |
   ▼
|---------------------|
| Manager(Supervisor) |
|---------------------|
  |        |        |                   
  ▼        ▼        ▼                    
|-------||-------||----------------|              
| Sup 1 || Sup 2 ||     Sup N      |               
|-------||-------||----------------|
                    |            |
                    ▼            ▼
             |------------|  |-------------|
             | TCP Reader |  | Other Child |
             |------------|  |-------------|

For each connection I start a GenServer in a supervisor… The GenServer init\1 calls connect\1.

  def connect(config) do
    case :ranch_tcp.connect(config.ip, config.port, []) do
      {:ok, socket} ->
        {:ok, socket}

      error = {:error, :econnrefused} ->
        Logger.error("Connection refused to #{inspect(config)}. Shutting down Reader")
        error

      error = {:error, _error} ->
        Logger.error(
          "CTC Socket failed to connect to #{inspect(config)}. Shutting down Reader"
        )

        error
    end
  end

What I want to do is let the Supervisor and its children die gracefully if :ranch_tcp.connect\2 returns {:error, :econnrefused}

The GenServer init looks like this

  @impl true
  def init(config) do
    case connect(config) do
      {:ok, socket} ->
#nice, start reading
        {:ok, %{:config => config, socket: socket}} 

      {:error, :econnrefused} ->
#too bad. Close self and Supervisor gracefully
        exit(:normal)

      {:error, error} ->
#What the what! Try again X times
        {:stop, error}
    end
  end

Observed behaviour

If the Genserver init\1 does not return {:ok, state} the error is propagated all the way to the Application, and it quits.

Starting ctc socket app

12:25:25.694 [error] Connection refused to %Server{ctc_name: :down_tcp_server, ip: {127, 0, 0, 1}, port: 5555, recv_buffer: 0}. Shutting down CtcReader

12:25:25.697 [info]  Application ctc_socket exited: CtcSocket.Application.start(:normal, []) returned an error: shutdown: failed to start child: Supervision.Manager
    ** (EXIT) shutdown: failed to start child: :down_tcp_server_supervisor
        ** (EXIT) shutdown: failed to start child: :down_tcp_server_reader
            ** (EXIT) normal
** (Mix) Could not start application ctc_socket: CtcSocket.Application.start(:normal, []) returned an error: shutdown: failed to start child: Supervision.Manager
    ** (EXIT) shutdown: failed to start child: :down_tcp_server_supervisor
        ** (EXIT) shutdown: failed to start child: :down_tcp_server_reader
            ** (EXIT) normal