If you’ve never received a message like this from your cloud provider, consider yourself lucky, because you will eventually:
Dear Amazon EC2 Customer,
One or more of your Amazon EC2 instances is scheduled for maintenance on 2016–01–01 for 2 hours starting at 05:00 UTC. During this time, the following instances in the us-east-1 region will be unavailable and then rebooted:
i-abcd1234
Your instance will return to normal operations after maintenance is complete.
This is essentially saying the node in question will be completely useless for two hours. Worse, AWS will sometimes notify us that our machine will be retired completely. Or, worst of all, a node might encounter an unscheduled issue. Our team maintains an infrastructure of over 500 AWS EC2 nodes, so events like this are not irregular.
Read more at FullContact Engineering
