[simscitizen]

Hot loading in Erlang is not magical. Here is an example. Let's say you want to redeploy some new code. In your deploy, you change some existing function foo in module A to call a new function bar in module B.

If you do this, you'd better make sure that you hotload the new version of B before you hotload the new version of A. Otherwise some process could end up trying to call B:bar through A:foo before the new B has finished loading.

If you rely on hotloading modules as your primary deploy mechanism, you will run into issues like this all the time. So it's not really clear to me that hotloading is a win for your typical stateless web service compared to just deploying a new binary and doing your standard zero-downtime deploy via forking.

It makes more sense when you realize that certain Erlang apps build up a huge amount of state in-memory. In those cases hotloading allows you to load new versions of the changed modules without having to take down the whole VM.