I don't know where you're getting your information, but your claims do not match my experience or, apparently, that of pretty much anyone else using Play (embedded Netty) or Dropwizard (embedded Jetty with a handler). Or anyone who is writing a Rails app or a Django app or anything else that lives as a standalone HTTP handler.

I have a Puppet script that sets up deployment on a new server. Puppet does not care how many machines the application is running on. Neither does the load balancer/reverse proxy in front of it; it takes a list of IPs and does its thing across them.

I have never seen an app server do anything that wasn't essentially this process, only with more XML and aggravation.