Author of the post (and Phoenix/LiveView/FLAME) here! I'm happy to answer any questions about how this works. The distributed features of the Erlang VM makes this kind of application outrageously easy to implement. And with FLAME you can elastically scale it with a couple lines of code.
My goal with FLAME is to move us as an industry away from the silly places serverless has taken us.
The demo app linked in the post is here if you want to speed test your own applications:
https://worldpagespeed.fly.dev/
