I'm not sure Erlang with a immutable infrastructure concept is good idea. Dynamic code reloading and upgrading without downtime is a key feature of Erlang, and

I'm not sure Erlang with a immutable infrastructure concept is good idea. Dynamic code reloading and upgrading without downtime is a key feature of Erlang, and immutable infrastructure do not play well with these features. If you make Erlang immutable, you should add another layer to ensure availability like HAProxy, which adds management burden. If you use dynamic code reloading, it is no longer 'immutable'.