Bringing child nodes up on network

I’ve been able to setup child nodes, but I’m trying to get them online. The intention is to make the nodes act as separate computers, such that I can broadcast messages to them via udp.

Code I’ve been using for parent node:

Node.start(:master@localhost, :shortnames)

(When running :longnames, I get a name error when initializing child nodes)

Code for initializing child nodes:

defmodule Child_Nodes do

  def init child_names do
    :os.cmd('epmd -daemon')
    for child_name <- child_names do
      {:ok, node} = start_child child_name
      load_code node

  def project_module_path do
    Path.absname('_build/dev/ebin') |>

  def start_child name do
    :slave.start(:localhost, name)

  def load_code node do
    :rpc.block_call(node, :code, :add_paths, [:code.get_path()])
    :rpc.block_call(node, :code, :add_paths, [project_module_path()])

This allows me to run my projects code on the child_nodes and access them using However, each node are going to find eachother over udp using this module, with different ports:

defmodule Broadcasting do

  @broadcast_timeout 1000

  @localhost {10, 0, 0, 68}

  #Node-name format: OrderHandler_<port>@<address>

  def init port do

    {:ok, socket} =, [active: true, broadcast: true])

    Task.async fn -> broadcast socket, port end

    IO.puts "Node at port #{port} initialized"

    listen socket, port


  def broadcast socket, port do

    :gen_udp.send(socket, {255,255,255,255}, port, to_string(port))


    broadcast socket, port


  def listen socket, port do

    local_msg = to_string(port)

    receive do

      {:udp, _socket, _address, port, ^local_msg} ->

        IO.inspect port

        IO.puts "localmsg"

        listen socket, port

      {:udp, _socket, address, remote_port, _msg} ->

        string_address = ip_to_string(address)

        IO.puts "new node added at port: #{port}"

        #"OrderHandler_" <> to_string(remote_port) <> "@" <> string_address |> String.to_atom |>


        "OrderHandler_" <> to_string(remote_port) <> "@localhost" |> String.to_atom |>



  def ip_to_string ip do

    :inet.ntoa(ip) |> to_string()



Is it possible to bring all child nodes online?

What is going to call this broadcasting module? A task? I think this is a place you should use gen_servers.

Also, the nodes have to be on the same layer-2 network that supports udp broadcasting and most major cloud providers don’t support this.

You might need to give beam.smp special setuid permissions (CAP_NET_RAW iirc) for it to be able to broadcast.

Finally you may run out of udp connections if you’re using nf_conntrack on Ubuntu 18.04.

The plan was to simply spawn the broadcasting procedure in each child node:

for node <- Node.list() do
Node.spawn(node, fn -> Broadcasting.init('uniqe ports') end)

The thing is that they aren’t able to find each other once the broadcasting starts.
This isn’t going to be a long-time robust solution, it is only going to be a replacement for the lack of computers atm

What’s the result of gen_udp.send?

iex(2)> Node.start(:master@localhost, :shortnames)
{:ok, #PID<0.275.0>}
iex(master@localhost)3> Child_Nodes.init(['1', '2', '3'])
[:ok, :ok, :ok]
iex(master@localhost)4> Node.spawn(:'1@localhost', fn -> Broadcasting.init(3456) end) 
iex(master@localhost)5> Node at port 3456 initialized
iex(master@localhost)5> new node added at port: 3456
iex(master@localhost)6> Node.spawn(:'3@localhost', fn -> Broadcasting.init(3455) end) 
iex(master@localhost)7> Node at port 3455 initialized
iex(master@localhost)7> new node added at port: 3455

They are able to detect themselves, but not each other

What is the result of :gen_udp.send? Can you IO.inspect it?

Sorry, for the late reply, inspecting the :gen_udp.send was a good idea:

iex(master@localhost)4> Node at port 3456 initialized
iex(master@localhost)4> new node added at port: 3456
iex(master@localhost)4> :ok
iex(master@localhost)4> {:error, :closed}