global singleton gen_server

[Roger Lipscombe]

Define "cluster start". In normal operation, there's nothing stopping
another node from joining the cluster at some arbitrary later time,
even days later. The first node to come up is a degenerate, single
node cluster, no?

On Thu, 16 Dec 2021 at 11:00, Roberto Ostinelli <ostinelli@REDACTED> wrote:
>
> Dear all,
> I'm trying to run an operation only once on cluster start but there's clearly something that I'm missing in the global module (see other related question here [1]).
>
> Therefore this time I'm trying to have a single global gen_server which I start directly from application start/2 callback with:
> gen_server:start_link({global, ?MODULE}, ?MODULE, [], Options).
>
> Nodes are already connected at that point (I can see them with nodes()), however for some reason this registration works on all the nodes and I find myself with multiple gen_server registered globally.
>
> What is the proper way to register a global singleton gen_server at cluster level on application start? mY need is to run an operation only _once_ a cluster boots up.
>
> [1] http://erlang.org/pipermail/erlang-questions/2021-December/101781.html