New – Modify EC2 Reserved Instance Reservations

By making good use of Amazon EC2’s Reserved Instances (perhaps guided by the recommendations of the AWS Trusted Advisor or equally capable third-party tools) you can lower your compute costs while also reserving capacity.

Today we are making the Reserved Instance model even more flexible by giving you the power to modify your Reserved Instances (RI’s) when your needs change. You can now move your RI’s between Availability Zones as long as you stay within the same Region. If your AWS account is enabled for EC2-Classic, you can also move your RI’s between EC2-Classic and EC2-VPC. You can now make adjustments to your Reserved Instances as your needs and your architecture change.

Let’s take a tour so that you can see how it works. I’ll use the AWS Management Console, but you can also modify your RI’s using the EC2 API‘s or the AWS Command Line Interface (CLI).

Open up the EC2 console and click on Reserved Instances. Select the RI’s that you would like to modify, and then click on the Modify Reserved Instances button:

The console will show your existing RI’s in groups (all RI’s that share the same Region, Instance Type, Product, Tenancy, Offering Type, Term and End Date/Time will be members of the same group):

You can use the Count field to modify some or all of the instances in each group, and you can use the Add button to insert additional rows to specify further modifications. You can choose to modify the Availability Zone and/or the Network Platform (if your account is enabled for EC2-Classic):

Don’t fret if your AZ menu doesn’t have the same number of zones as mine. This just means that my AWS account is a little bit older than yours and has access to more zones.  The modifications that you specify must address all of the RI’s in each group.

Click Continue, review your request to make sure that it is accord with your needs, and then click Submit Request to initiate the specified modifications.

Once initiated, each of the modifications will either succeed or fail within two hours. You will see the state of your existing Reserved Instances change, and you will see new Reserved Instances created as the modification proceeds.

You can refresh the console to track the status changes. When none of the status messages contain “pending”, the modification process is complete.

Here are a few things to keep in mind as you start to make use of this new feature:

• Availability of Reserved Instances changes constantly. Therefore, each modification request can succeed or fail on its own. If a particular request fails, you can issue it another time.
• You can only modify active Reserved Instances that you own, that are not currently listed for sale in the Reserved Instance Marketplace.
• The Availability Zone and the Network Platform that you request must be available in your account.
• Modifications take effect as soon as possible, and the pricing benefit starts to apply at the beginning of the current hour.
• If your Reserved Instance cannot be modified, it will retain its original properties.

Oh yeah, one more thing – when you purchase an RI you get two separate benefits: lower hourly pricing and capacity assurance. The capacity assurance is specific to the Network Platform of the RI. The pricing benefit, however, is not. In other words, if you purchase an RI for one of our cc2.8xlarge instances, you will get the pricing benefit regardless of which Network Platform you use, but you will only get the capacity assurance within the Network Platform of the RI.

I hope that you enjoy this new feature and that you find it useful. Leave me a comment and let me know what you think.

— Jeff;