My customer's site is running following versions
$ rails -v
Rails 2.3.5
$ ruby -v
ruby 1.8.6 (2010-02-05 patchlevel 399) [x86_64-linux]
This project consists of following steps
1. backup current version
2. applying the security patches referenced on [login to view URL]
3. in case it fails solve the problems
This site is in production but there is no problem that is down for 1 hour or so.