[Muromec]

There can't be anything atomic in a distributed system. You can't even atomically hot upgrade it on a single VM anyway -- you instead load the new version of the module and let dispatcher know to route new calls into it, the same as you would do with a load balancer and a bunch of load bearing docker hosts, just inside your app.

[knome]

erlang has a code_change function in the otp that allows the gen_server to update its current state and start using new code. No connections need be broken with clients, no long running processes need be stopped. Just updated in place.

It's not just a routing change.

https://www.erlang.org/docs/24/man/gen_server

[Muromec]

It's a routing change in a sense that gen_server is routing function calls to the new module definition. I know about gen_server and code_change, the point was that conceptually the same mechanism, just on a different level of abstraction.

[knome]

Routing in progress connections to a new module seems a rather different thing to me than merely routing new ones.