** exception exit: noconnection

[Lukas Larsson]

On Tue, Dec 3, 2019 at 11:56 AM Adam Lindberg <hello@REDACTED> wrote:

> Hi!
>
> I’m running some tests using distributed Erlang. I set up a cluster of
> Erlang nodes doing Distributed Systems™ stuff, and a hidden node that have
> a connection to each of the nodes in that cluster. The hidden node
> orchestrates the test by starting all Erlang nodes as ports. It then starts
> a process (gen_server) on each node that manipulates stuff on that node. It
> also loads some mock modules among other things. The hidden node also has
> some managing gen_servers running locally, which some of the mocks makes
> RPC calls to from the cluster nodes (to simulate and orchestrate mocked
> hardware components).
>
> Now I wanted to test how my system behaves when killing some random nodes,
> chaos monkey style. So I picked the easiest option of using
> rpc:cast(RandomClusterNode, erlang, halt, [137]). However, now my test dies
> with the following obscure error: ** exception exit: noconnection. This
> even happens when first spawning a fun that then calls erlang:halt(137) (as
> to avoid the RPC connection somehow breaking).
>
> After searching a bit on the Internet it seems to be some internal
> uncatchable (!) error generated by Erlang [1][2], but it is not at all
> clear when it happens, and how to avoid it. After some debugging in the
> gen_servers running on the hidden node, I can see the error by setting
> process_flag(trap_exit, true) and printing it in terminate/2 but I still
> can’t catch it. I can’t even catch it in the shell by enclosing my run in a
> try-catch block! It’s almost not mentioned at all in the official
> documentation [3]. Most likely I’m setting up my test nodes and the
> application/test code in a way that generates this error, but I have no
> idea what exactly leads to it.
>
> I guess I have two problems:
>
> 1. What is the error, and how can I handle / avoid it?
>

I'm not sure, but could it be that your process is linked to a process on
the remote side? That what you are getting is a broken link error?


> 2. Why is it not documented?
>
> Cheers,
> Adam
>
>
> [1]: http://erlang.org/pipermail/erlang-questions/2012-April/066219.html
> [2]: http://erlang.org/pipermail/erlang-questions/2013-April/073246.html
> [3]: http://erlang.org/doc/getting_started/robustness.html
>
>
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