Amazon Web Services reserved instances used to be a stodgy lot. You had to commit to a certain instance size — which could not be changed — and to a particular availability zone, which also could not change. Things are starting to loosen up, however.
As of Thursday, you can start moving your reserved instances between availability zones within the same region. From an Amazon post Wednesday night:
We are excited to announce the ability to migrate your Amazon EC2 Reserved Instances (RIs) between Availability Zones in the same Region and between Network Platforms (to and from Amazon VPC).
Reserved instances are functionally the same as on-demand instances but can be less pricey if you commit to long term usage — they are available for one- or three-year terms. Less pricey that is, if you actually end up using them for the whole term. If you let them lie fallow, they may not be your best option.
Cloudability, an AWS watcher that aims to help customers get the most of their AWS resources, is clearly on the ball. It posted about its tool to help users use reserved instances effectively Wednesday night as well.
Reserved Instances are often the most effective way to reduce your AWS infrastructure costs. But it can take hours to calculate how many reservations you need — and if you buy the wrong quantity or types of Reserved Instances, you could end up spending more money than you save. That’s why Cloudability is pleased to announce the beta release of a new tool that gives you accurate Reserved Instance purchasing recommendations instantly and without the risk of spreadsheet errors. Say “hello” to the Cloudability Reserved Instance Planner.
Below is the Amazon FAQ about reserved instance restrictions from before the latest change. I would guess that as more flexible cloud competition comes on line, we’ll see AWS loosening some of these restrictions as well.