When spawning a remote process like this, does the ‘work’ (1+2 in this case) get evaluated on the local node?

Arguments (it’s just a normal list) are “evaluated” on the calling node, the function is executed on the remote node.

It’s the same as:

iex(dev@127.0.0.1)> caller = self()
iex(dev@127.0.0.1)> args = [caller, {:response, Node.self}]
#==> [#PID<0.114.0>, {:response, :"dev@127.0.0.1"}]

iex(dev@127.0.0.1)> Node.spawn(:"suv@127.0.0.1", Kernel, :send, args)
iex(dev@127.0.0.1)> flush()
#==> {:response, :"dev@127.0.0.1)"}

You can make the called function process its args and then that part would be handled by the remote node too:

iex(suv@127.0.0.1)> defmodule Worker do
                      def do_work, do: {:response, Node.self()}
                    end

iex(suv@127.0.0.1)> Worker.do_work()
#==> {:response, :"suv@127.0.0.1)"}

# -------------------- back to dev@127.0.0.1 -------------------------

iex(dev@127.0.0.1)> :erpc.call(:"suv@127.0.0.1", Worker, :do_work, [])
#==> {:response, :"suv@127.0.0.1)"}

:erpc.call here just executes the function remotely and sends back the results, similar to your Node.spawn example with send. I just wanted to mention it as it’s a pretty useful module.

I would guess that the closures capture module versions (MD5 by default) in addition to module and function names and since they are different in different versions of Elixir, it results in an error. And maybe sending Node.spawn(:"suv@127.0.0.1", Kernel, :send, [caller, {:response, 1+2}]) doesn’t concern itself with module versions and just runs apply(Kernel, :send, [caller, {:response, 1+2}]) so it works across Elixir versions. But it can possibly produce different results from if this was executed locally. But I guess that’s usually expected with distributed systems.