[FooBarWidget]

(FYI I'm a Phusion Passenger developer.) I find it interesting that you think the shared socket performs better than letting a proxy distribute the load. I've also done some tests and I find that the shared socket harms performance on high concurrency situations because of the so-called thundering herd problem. The problem is that all Unicorn workers select() on the socket, but when a client comes in all workers are waken up, all of them try to accept() the client but only one succeeds, and the rest goes to sleep. We're working on some pretty heavy performance and scaling optimizations for the upcoming Phusion Passenger 3 and we've found that avoiding the shared socket gives us much better overall performance. It'll be nice if the kernel provides an interface for performing select() and accept() in a single atomic operation but until then I think the shared socket isn't that good.

From what I've seen so far, peoples' experiences with both Phusion Passenger and Mongrel/Unicorn can vary drastically. Some people noticed a huge response time drop and performance increase when they switch from Mongrel/Unicorn to Phusion Passenger, others experience the opposite. I guess it depends a lot on the server. Phusion Passenger has got some pretty heavy users though, e.g. the New York Times Obama real time election results page was running on Phusion Passenger. The Dutch national TV broadcasting organization is running all their Rails apps on Phusion Passenger and they get huge spikes of traffic whenever something is mentioned on TV.