[galaxy-dev] Portability and versionig in Galaxy

Hi All, I am completely new to galaxy but part of my PhD research is to look at portability issues of workloads across different versions. I've tried looking at the wiki and the various pieces of documentation but no luck so far. Can someone please point me to a document or tutorial that explains how this is currently done in Galaxy and also any issues/gaps that may be worth addressing? I am also generally interested in how Galaxy works "under the hood". Is there a document that explains the architecture and design? Many thanks in advance! Sally.