God knows what the standard will be when we start using IPv6, but I guess a datacentre would allocate each server a prefix of a few thousand ips. The server is then free to use any of them without any risk of collision. The point of this vast address space is precisely to enable the infrastructure to be a lot more stateless (as in not worrying about individual IPs).

> You can ask the OS to allocate a new port when you start up a piece of software and then advertise that port via whatever coordination protocol you have.

As long as the coordination protocol is not output a wrongly formatted url to the terminal and have the user cut and paste it into their browser, the coordination protocol should be able to handle it.