This article is from 2009, and while many of the points it makes are still valid, there is at least one that isn't: > As a result, it ONLY makes sense to consi

This article is from 2009, and while many of the points it makes are still valid, there is at least one that isn't: > As a result, it ONLY makes sense to consider a dedicated instance for a machine that will be running 24 hours a day, 7 days a week. Amazon have addressed this with their Light, Medium and Heavy RIs. The break-even points on the cost savings are on this page: http://aws.amazon.com/ec2/reserved-instances/ http://aws.amazon.com/ec2/reserved-instances/ The one thing I would add about RIs is: they only apply to a pairing of AZ and instance size. They suit people who scale out (adding more instances) and don't suit people who scale up (changing their instance sizes and not using the old reservations).