Google Servers Migration Paper

This has to be the coolest paper I 've read in a long time. It explains how a few engineers working at Google, migrated thousands of servers from the ancient RedHat Linux 7.1 to a modern version of Debian, with minimum downtime, by replacing small bits of the operating system at a time, in many many iterations.

The paper is from a USENIX Conference, here you go, and you're very welcome: Live upgrading thousands of servers from an ancient Red Hat distribution to 10 year newer Debian based one.