Erlang supports hot code migration, which allows you to use your new code in each process AFTER you merge the new code in. The processes that were running when

Erlang supports hot code migration, which allows you to use your new code in each process AFTER you merge the new code in. The processes that were running when you merged the new code will still be using the old code, until they end execution. This isnt really that big of an issue if you write your code in the erlang-way, which is using as many processes as you can to spread data, and then passing messages between the different processes. In this situation,each HTTP session would probably be running the old code, but each new one created would be running the new code.