Well, that's stated in the article, no?
Source code replication was rather easy. We have a custom Drupal module (Release Management Module) which uploads files from our STAG server to our PROD server. This module checks the filetree on te STAG server, and compares it with host1 and host2. So if a file is missing on the production servers, it will try to upload it. If it changed, it will override the files on production. And if it was deleted, it will delete it on PROD too. This Release Management Module can be be compared with the diff program on a UNIX/LINUX system. The Release Management module extends diff by adding an option to add/change/delete.
This module is a custom module and not contributed to the community. If you want the source code, I'm afraid you will have to ask it to helpdesk [ A T ] pipa.be