A few years ago, the biggest problem with Erlang's hot code updates was getting the files updated on all of the nodes. Has this been solved or improved in any way?
I don't think updating files is the problem. The biggest issue with hot code updates seems to be that they can create states that cannot be replicated in either release on its own.
This is my experience. About 25% of the time I'd encounter a bug that's impossible to reproduce without both versions of the code in memory, and end up restarting the node anyway dropping requests in the process. Whereas if I'd have architected around not having hot code updates I could built it in a way that never has to drop requests