Hi friends,

This topic has come up a handful of times before on the forum, but I wanted to solicit some advice on how to debug an attached node connection issue I’ve started to experience with Livebook.

Context & setup

This setup was previously working. In fact, I posted on this forum to share how I got it set up and the script I was using to start the Livebook server with the correct flags. Sometime in the last couple of weeks, this setup has stopped working. I’ll describe exactly what I’m seeing a bit further down.

To get it out of the way, here are the versions of everything I’m using:

• Latest Livebook - 0.8.1 (though also tried with 0.7.2, 0.7.1, and 0.7.1)
• Latest Elixir/OTP - 1.14.3 / 25.2.1 (using same versions both locally and on server)

Other bits and bobs:

• Connection is through a wireguard tunnel between me and the server, as described in this article on fly.io.
• The node name and cookie is being set as expected.
• Livebook is being started with -proto_dist inet6_tcp.
• I am able to connect to the node through iex - more on that below.

Description of issue

After launching the Livebook server, opening a notebook, and attempting to connect to the attached node, Livebook hangs until the terminal eventually reports this error:

12:35:20.007 [error] GenServer #PID<0.592.0> terminating
** (CaseClauseError) no case clause matching: {:badrpc, :nodedown}
    (livebook 0.8.1) lib/livebook/runtime/erl_dist.ex:74: anonymous fn/3 in Livebook.Runtime.ErlDist.load_required_modules/1
    (elixir 1.14.3) lib/enum.ex:2468: Enum."-reduce/3-lists^foldl/2-0-"/3
    (livebook 0.8.1) lib/livebook/runtime/erl_dist.ex:71: Livebook.Runtime.ErlDist.load_required_modules/1
    (livebook 0.8.1) lib/livebook/runtime/erl_dist.ex:60: Livebook.Runtime.ErlDist.initialize/2
    (livebook 0.8.1) lib/livebook/runtime/attached.ex:45: Livebook.Runtime.Attached.connect/1
    (livebook 0.8.1) lib/livebook/session.ex:1519: Livebook.Session.handle_action/2
    (elixir 1.14.3) lib/enum.ex:2468: Enum."-reduce/3-lists^foldl/2-0-"/3
    (livebook 0.8.1) lib/livebook/session.ex:878: Livebook.Session.handle_cast/2
Last message: {:"$gen_cast", {:queue_cell_evaluation, #PID<0.594.0>, "setup"}}

Critically, I am able to connect to the node manually through IEx. I can start a local iex using the following command, connect to the remote node, and run some code through Node.spawn(server, ...).

# ERL_AFLAGS="-proto_dist inet6_tcp" iex --name local@127.0.0.1 --cookie my-shared-cookie
iex> server = :"my-server-node-name@some:ipv6:address"

iex> Node.connect(server)
true

# Test module that prints "hello"
iex> Node.spawn(server, Hello, :world, [])
hello
#PID<...>

I’m not really sure where to go from here. Any suggestions would be greatly appreciated!