How do I modify my Convertible Reserved Instance after I resize my Amazon EC2 instance?

Short description

To receive the same Reserved Instance discount that you had before you resized the EC2 instance, you must adhere to the modification requirements. You must also keep the same instance footprint.

Some instance platforms, such as SUSE or Red Hat Enterprise Linux (RHEL), don't allow for instance flexibility. For these platforms, you can modify the Availability Zone and scope of the Reserved Instance. However, the instance must stay within the same family and generation. You can divide or merge existing Reserved Instances into different instance sizes across the same family if the footprint of your reservation remains the same.

Resolution

Note: To calculate your instance footprint, see Instance size footprint. You can also use a Savings Plan instead of Reserved Instances. For more information, see Should I use Savings Plans or Reserved Instances for my EC2 instance?

If your instance allows flexibility, then submit an instance modification request to request an updated instance size. If the instance doesn't allow flexibility, then take the following actions based on your requirements.

Size up an instance for a type that doesn't allow flexibility

In this example, you have a r5.16xlarge SUSE Linux instance. You purchased a matching Convertible r5.16xlarge Reserved Instance for a specific AWS Region. Your application requirements changed, and you now require a larger r5.24xlarge instance. You can't use instance flexibility for SUSE instances, but you want to keep the discount that the r5.16xlarge Reserved Instance provides.

To resolve this issue, purchase an r5.8xlarge Reserved Instance, and then submit a request to merge the new instance with your existing r5.16xlarge Reserved Instance.

An r5.24xlarge instance has a footprint of 192 units, so you require a Reserved Instance with a matching footprint. An r5.16xlarge instance has a footprint of 128 units and an r5.8xlarge Reserved Instance has a footprint of 64 units. Together, the two instance footprints cover the larger r5.24xlarge running instance.

Use more instances with fewer resources for a type that doesn't allow flexibility

In this example, you have a Regional, Convertible Reserved Instance to cover four units of a t2.large RHEL instance. Your requirements changed, and you now need four t2.small instances of 1 unit each behind a load balancer.

To resolve this issue, submit a modification request to turn the t2.large reservation into four t2.small reservations to cover your newly launched instances.

Related information

How Reserved Instance discounts are applied

Differences between Standard and Convertible Reserved Instances