Commencing shortly after midnight and lasting anywhere from 15 minutes to several hours, depending upon how smooth things go, There is a problem with the 3.15.0 kernel drivers for E1000 Ethernet chips which my machines happen to use that causes them to periodically hang for about ten seconds. Most people will experience this as pause in I/O but some non-Linux versions of ssh will timeout and disconnect. I have been working with Canonical to come up with a fix. The first kernel they provided did improve the situation so that it happened a few times a day instead of a few times an hour. They have another kernel for me to try.
So tonight, I will be installing that kernel and rebooting to make it active. I am going to attempt this remotely but in the past sometimes network would not come up after a reboot and if that happens I will need to drive down to the co-lo facility and it will take longer. This will interrupt all services as it affects both the machines hosting the virtual machines and the NFS servers that hold your home directory, mail directory, and a few other common file systems.
I plan to start this work around 12:30AM and if things go well, I should be finished by 1AM, if not it may be as late as 3AM Pacific time.