- We deployed tarballs to production machines which unpacked to a single directory that included a virtualenv that had both all our code and all the modules we relied on, and anything else that the code needed to function that wasn't installed in a very basic RHEL install.
- We used the --relocatable option in virtualenv to remove all references to absolute paths, which meant we could copy the virtualenv around to various directories and machines and still have it work.
- We had a series of makefiles that would make/update a virtualenv, and which worked on both mac and linux. We would use this both in development and when deploying. For several packages, we had to hand tune this to work on both mac and linux, but for most things, it Just Worked.
- When we deployed to production, we would unpack the tarball to a directory whose name included a version number for the push. We then had a symlink that pointed at the currently running version. This meant all we had to do to rollback a push was flip the symlink to the previous deployment directory, and restart. This rollback included any modules that changed (since they were in the virtualenv). I haven't seen any other way to reliably do this.
The one thing you mention that we didn't have to deal with was mixed 32/64-bit environments. One nasty solution is to have two build machines, one 32-bit and one 64-bit, but there's probably a better way...
