Hi.
Thanks for putting the library together.
Before I found it, I’ve been trying to hack my own implementation and I ended up with a very similar code as yours.
However, both your code and mine suffers from an unexpected behavior.
When a 2nd node joins the cluster, I do see:
23:24:54.246 [info] global: Name conflict terminating {:singleton, #PID<18487.303.0>}
But what is unexpected is that not only the singleton process is terminated, but the whole application on one of the nodes:
23:25:47.517 [info] Application wpc5_singleton exited: killed
And one of the nodes basically is left in a state where my own application is not running, only the “libraries” continue running.
I’ve been struggling with the same issue in my own implementation.
I created a DynamicSupervisor for the singleton process, similarly to you and I was hoping that it will “shield” the main Application supervisor from crashing when the :global registry kills one of the singleton processes.
However, that doesn’t seem to be the case and the whole application dies regardless of multiple layers of supervisors 
Using Elixir version 1.12.3
