Calling a GenServer on a remote machine

Is the device you deploy Nerves on, and your workstation have similar CPU architecture, i.e. both are ARM or both are Intel CPU instruction based? I never tried if it actually is a problem, but endianness may be a problem Endianness - Wikipedia if you try talking between x86 and ARM64 nodes in the cluster.

But answering your question, you can use Horde, and in particular Horde.Registry Horde.Registry — Horde v0.10.0 to register the Pids of all the GenServers in the cluster and then use it just like normal Registry to find those Pids. The APIs are the same. I am using it in the homogenous cluster of the same machines and it works great, again, I am not sure if the endianness won’t mess it up.

This is a bold statement, do you have any sources that can confirm this?

Also curious about the endianness, as I’ve only done homogeneous clusters, but I wouldn’t have thought it would be an issue as it is being packed by BEAM.

For instance, I had to receive/decode a packet from an Erlang machine and it took me a minute to realize that the packet header (2-bytes to indicate the size of the packet) was in big-endian format.

No, and it’d be interesting to see what works and what doesn’t work.

I am mentioning it because I saw the erlang/elixir code explicitly handling endiness in some blog posts about handling data from smart sensors, and I suspect that the distribution protocol will handle it just fine but the payloads you send between nodes may require conversion. For example: Smart Sensors with Erlang and AtomVM: Smart cities, smart houses and manufacturing monitoring - Erlang Solutions

Well that is another question.

I am not entirely sure, but my thinking is that inter-node communication is using functionality from term_to_binary, there seems to be a more comprehensive documentation here: External Term Format — OTP 29.0.2 (erts 17.0.2)

Hi.
Maybe the Spawn project GitHub - eigr/spawn: Spawn - Actor Mesh · GitHub (I’m a co-creator) can help you. If you need, you can open a discussion in the repository and we’ll continue there. Or on our discord channel (link in repo).

Hey thanks for the suggestion! While I am on different architectures (ARM Raspberry Pi 3 vs Intel Mac), I haven’t run into endianness as an issue yet. I do have to be careful about endianness when reading the sensors, because each one is different according to its own data sheet. However, when sending messages between BEAM nodes I haven’t had any issues. I assume that it is taken care of by term_to_binary as mentioned by @D4no0. If I run into any while testing though, I’ll be sure to update here!

Horde.Registry looks like a decent option. I do notice that it looks like I would have to structure my whole application around using their registry instead of the built-in one. I’d like to avoid that, but it would work for debugging purposes.

What I was thinking is that for Nerves application.ex, we have a pathway to configure different supervision trees based on the MIX_TARGET the code was compiled for - see below:

defmodule MyApp.Application do
  @moduledoc false

  use Application

  @impl true
  def start(_type, _args) do
    opts = [strategy: :one_for_one, name: MyApp.Supervisor]

    children =
      [
        # children for both targets here
      ] ++ children(target())

    Supervisor.start_link(children, opts)
  end

  # List all child processes to be supervised
  def children(:host) do
    [
      # children for host

      # possible to do some sort of "remote" sensor here?
      {MyApp.Sensor.Remote, node: "nerves@nerves.local"}
    ]
  end

  def children(_target) do
    [
      # children for targets
      {MyApp.Sensor, polling_interval: 1_000}
    ]
  end

  def target() do
    Application.get_env(:my_app, :target)
  end
end

It would be nice to have that functionality available in a lightweight way - ie, only have the changes apply on the host side

Looks interesting! I’ve not heard of the project before. After a Quick Look through the docs though, it looks a little more heavy-weight than I think I need in this situation? I don’t have a DB and not using Kubernetes. Was there a specific module in the project you think would help that I can look deeper into?