To clarify, my understanding is that while rails is restarting, Passenger will queue all the requests that come in and begin processing them as soon as rails is ready. But yeah, zero downtime, it's pretty awesome.
Yeah. We load balance across 5 Apache/Passengers and I do rolling deploys (all in Capistrano) by removing a Passenger from load balancing, updating the app, restarting Apache, and adding it back into load balancing with a 10 second delay between each. We tried the Passenger touch restart.txt and that didn't go well at all when we were under load.
He has been kind enough to share about his setup quite a lot about lately. In fact, looks like it's on the HN homepage right now: http://news.ycombinator.com/item?id=872301
Also, if you're using Monit to watch the memory bloat of your passenger processes, when you kill one process it tends to do the same stalling thing on all your processes until the ONE you killed is back up.
