Confusing error when trying to start Genserver for multi-node testing

Questions & Help Questions
, ,
8

I ran into a similar issue while running tests in a similar environment.

What I think is happening is that the slave node is being started, but none of the modules from your master are loaded onto the code server for the slave. Here’s the blog post I read (in two parts) where I uncovered and figured out the solution: https://medium.com/@stavro/intro-slave-nodes-and-remote-code-loading-d1168bff7b20

Basically you have to point the slave node to the path where the .beam files live, so it can load it into its code server. This is done using :code.add_paths/1

Here’s what I did that seems to have solved the issue:

defmodule MyAppTest do

  use ExUnit.Case, async: true

  test "distributed test" do
    :net_kernel.start([:node1, :shortnames, 3000])
    {:ok, slave} = start_slave

    # rest of the test
  end

  defp start_slave do
    {:ok, hostname} = :inet.gethostname()
    {:ok, slave} = :slave.start(hostname, 'slave')
    :rpc.block_call(slave, :code, :add_paths, [:code.get_path])
    {:ok, slave}
  end
end