Distributed software upgrade

Working with distributed software is always a pain, the upgrade of the software is always a difficult part doesn’t matter how you look at it: data structure, data, code itself.

One of the issues of the software upgrade is that not all “nodes” are available all the time and because of it an upgrade may need to be done in different moments in the “nodes”. Another complication is that even with a “node” connecting it may have another version because the upgrade failed or was not executed by the user.

I am always curious about this topic, mainly because I see the complications about it everyday. So I would like to share an interesting paper that I just read:

“Modular Software Upgrades for Distributed Systems” by Sameer Ajmani, Barbara Liskov, and Liuba Shrira. In European Conference on Object-Oriented Programming (ECOOP), July 2006.[pdf]

Abstract

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. We present a methodology and infrastructure that make it possible to upgrade distributed systems automatically while limiting service disruption. We introduce new ways to reason about correctness in a multi-version system. We also describe a prototype implementation that supports automatic upgrades with modest overhead.

It is a really interesting paper, even if you can’t use such approach the problem and ideas are always helpful.

Also remember that it is not only about having distributed software clients, in this clustered world the change of having a cluster with an older version is likely and completely acceptable. It is not because your world is the server side that it doesn’t concern you.

Enjoy it listening to I will waitfrom Mumford & Sons.