" Software Upgrades in Distributed Systems "
Barbara Liskov, University of Oklahoma, Part of the Oklahoma Computing Conference

Upgrading the software of long-lived, highly-available distributed systems is difficult. It is not possible to upgrade all the nodes in a system at once, since some nodes may be unavailable and halting the system for an upgrade is unacceptable. Instead, upgrades must happen gradually, and there may be long periods of time when different nodes run different software versions and need to communicate using incompatible protocols. This talk describes an infrastructure that make it possible to upgrade distributed systems automatically while limiting service disruption. It also describes a methodology for upgrades, including a new way to specify upgrades.