[toast0]

After using hot code loading in production for the last 5 years, I don't see why you wouldn't use it, when it's right there. Maybe it's less thought to do a rolling restart, but it's a lot more effort expended by everything in the system to rebuild all the state that was in your processes.

A behavior is simply a list of functions you've declared that your module will export -- and a convention on what they might do. gen_server.erl is going to make lots of callbacks into your code, and rather than pass a huge list of funs, instead we pass the module name, and gen_server calls the exported functions from that module (this style means all the callbacks will hit your new code if you hot load, without you doing anything special; processing type changes is up to you, of course)