Well, this is a week that will be remembered for awhile. A major, but undisclosed, Xen hypervisor issue forced Amazon, then Rackspace, to reboot a good chunk of their public cloud instances.

A rough timeline:

• Wednesday night (eastern time): Amazon notifies customers about the undisclosed issue, saying it will start rebooting instances on Friday.
• Thursday morning: Amazon posts a blog with a bit more information.
• Friday: [company]Amazon[/company] starts rebooting what it says is 10 percent of its total EC2 instances.
• Friday night: [company]Rackspace [/company]notifies its customers.
• Sunday: Rackspace starts the reboot process.

It seems clear, as David Mytton, CEO of [company]Server Density[/company] noted in comments to an earlier story, that AWS and Rackspace got the same “predisclosure” notification re. the Xen issue, but took Rackspace took two days longer to respond, The most likely reason, Mytton surmised was that Rackspace was working on the proper process to handle the critical…