Hi everybody, this is my first time here so sorry if I make some mistakes.

I’m working on a little project for my thesis. During my study on Elixir I found the swarm library and it suites perfectly on what I need to do. The problem is that I have some troubles using it:

1. Process state handoff: I have a GenServer with a very simple struct and I need to distribute this worker around my cluster. When the node on which the worker is running goes down, Swarm resume the process on a new node but I cannot manage to resume the state. I’ve followed the worker example provided by the original author on github but it seems to not work. Here’s my code:

defmodule MyApp.Worker do
  use GenServer

  defstruct elements: %{}

  def start_link(opts \\ []) do
    GenServer.start_link(__MODULE__, opts, name: __MODULE__)
  end

  def init(opts) when opts == [] do
    state = %EventStore.Worker{}
    {:ok, state}
  end

  def init(opts) do
    state = opts
    {:ok, state}
  end

  def handle_call({:swarm, :begin_handoff}, _from, state) do
    {:reply, {:resume, state}, state}
  end

  def handle_call({:swarm, :end_handoff, state}, _from, state) do
    {:noreply, state}
  end

  def handle_cast({:swarm, :end_handoff, state}, state) do
    {:noreply, state}
  end

  def handle_cast({:swarm, :resolve_conflict, _delay}, state) do
    {:noreply, state}
  end

  def handle_info({:swarm, :die}, state) do
    {:stop, :shutdown, state}
  end

end

More details. I’ve used Swarm.register_name(workername, workername, :start_link, [opts]) for starting my GenServer and I’ve tried to kill the node via double CTRL+C and via :observer.start too. I really don’t know what is the problem since I’ve also looked at the Swarm tracker.ex file and saw that there’s a call with :begin_endoff which I (think) correctly handle in my GenServer. Indeed if I do the same call manually via shell, my worker handle it.

2. Same worker on more nodes: if I have a cluster of 3 or more nodes and I would like to run the same process on more nodes at the same time, how can I do? Because after the first registration using the same Swarm function mentioned above, Swarm warns me that there’s already that registered process.