[zelly]

There is no difference between the two because they are the same thing, just architected differently. The networking is done by, say, nginx rather than a server that is part of the application.

fastcgi applications can "scale to 0" and cost nothing when they are not used. An application server must always have at least one open socket on a running machine.

fastcgi would probably do better over http/2 than other protocols not designed for multiplexing.