An urgent security patch is needed on all the linux systems in GCE which requires a reboot. Beginning at 5PM this evening, we will start rolling these patches out. This will affect all GCE compute nodes, home nodes, login nodes, and workstations. In each case, the outage will be as long as it takes for the reboot to complete, which will be between 1 and 5 minutes, however any active sessions will be lost.
Sorry for the short notice, but such is the nature of security patches.