An important limitation to note is that while you can "just buy a second 2xlarge", you have to do it within the same hour: "When combining Reserved Instances,

An important limitation to note is that while you can "just buy a second 2xlarge", you have to do it within the same hour: "When combining Reserved Instances, the end dates of the Reserved Instances must have the same hour digits in 24-hour format" Source: http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ri-modifying.html http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ri-modify...