The default for Unicorn is to start a whole new set of processes, but it's pretty easy to set up a custom script that uses signals + the before/after_fork hooks

The default for Unicorn is to start a whole new set of processes, but it's pretty easy to set up a custom script that uses signals + the before/after_fork hooks to do various custom rolling restarts. The same goes with user switching, you can just use Ruby to do it (example at the bottom of https://gist.github.com/206253 https://gist.github.com/206253). Unicorn also already has "error resistance" in that it won't switch to a master/workers that aren't booting properly during a restart.