We will be having a maintenance window tonight from 23:00 to 23:59 PDT. A very small amount of web unavailability will be required during this period.
We will be upgrading some core libraries to versions that are not compatible with what is currently running, so all daemons must be restarted simultaneously. For this to go smoothly, we will be disabling the web app for perhaps 30 seconds.
UPDATE: Maintenance was completed successfully. Total web unavailability was a tad more than estimated at one minute and 40 seconds. Some job runners did not restart cleanly and as a result some jobs failed, but all job runners are operating normally now. If you experienced any problems during the maintenance window, don’t hesitate to contact us at http://support.github.com.
Couldn't you do some kind of rolling thing where you make the change to 1 machine at a time, or something? It's not really a big deal, but 0 downtime would be nice, and it doesn't seem like it would be that hard.
@jackowayed These upgrades involve backwards incompatible changes to client/server libraries. Any machine that is upgraded will stop working with all other machines until they are upgraded, so all upgrades must be done simultaneously. Fortunately, this type of upgrade happens extremely infrequently.