Thanks for the link.
Is this a regular way to deploy?
I mean, I saw there is Leinen or something like that for package management.
But once you run, you could still connect to an app that has been run in the usual way? Seems like a setup on top of it.
Or is is just independent?
It's regular, every production Clojure system has REPL access for devs.
You don't need it often, but when you do, it's invaluable. And the REPL is such a normal thing to use in Clojure, there's no reason not to do it.
This page should give you the answer: https://nrepl.org/nrepl/usage/server.html