After my previous article about Gentoo, I had the audacity to update the "mailman" package from version 2.1.5 to 2.1.9. While the mailman code itself had not changed much, Gentoo's way of structuring of the installed package had changed. It took me about 4 hours of uninterrupted work to get our mailing lists working again.
At this stage, you may think that I had learned my lesson, and would not embark on any new adventures. I had not yet realized my luck so far and would soon pay the price of my temerity.
On Torino, another production machine running Gentoo, my subsequent attempts at upgrading X11 and Apache resulted in complete failures. Notwithstanding my relentless attempts, Torino can no longer run X11, due to a suspected gcc/glibc versioning problem.
Updating of Apache from 2.0.x to 2.2.x had an interesting twist on its own. As in mailman, Gentoo's packaging structure for Apache changed between e 2.0.x and 2.2.x. More specifically, the directives for specifying which modules were included in the server changed. Fortunately, there were instructions on migrating from the old to the new structure. It took me about 2 hours to understand that the migration instructions had a little bug. Dashes within package names had to be written with underscore characters. After that tweak, the new build of the Apache server included all the required modules.
For our web-applications, we rely heavily on reverse proxying, that is on Apache's mod_proxy module. This module witnessed substantial enhancements between Apache 2.0.x and 2.2.x. Given that Torino is a production server, I had only a limited number of hours to perform the migration. At about 1 AM Monday morning, manually reverting to Apache 2.0.x was the only remaining option.
As I understand it, Gentoo supports the installation of only a single version for any given application package. It does not support the simultaneous installation of the same package. In the Apache case, it would have been nice to simultaneously support the installation of Apache version 2.0.x and 2.2.x. Alternatively, it would have been acceptable if Gentoo allowed me to revert to an older version of Apache. However, it seems that Gentoo supports only one path for updates, i.e. upgrades.
In conclusion, while Gentoo's package menagement mechanism is pretty fantastic, it still does not allow for seamless upgrades. Others have made similar observations.