AWS Regional Reserved Instances are now Resizable

With Regional Reserved Instances from AWS, you can have the flexibility of switching between availability zones for your RIs without having to modify or purchase new RIs. AWS has recently announced that all Regional Reserved Instances can be resized in a manner that allows you to easily switch an m4.4xlarge into 4 separate m4.large instances for example.

What is a Reserved Instance?

You can purchase Reserved Instances from AWS to save on your hourly EC2 costs and also “reserve” compute capacity to ensure that you always have the specific instance types required regardless of the current availability of On Demand instances. The following types of Reserved Instances are available:

  • Standard RIs: These provide the most significant discount (up to 75% off On-Demand) and are best suited for steady-state usage.
  • Convertible RIs: These provide a discount (up to 45% off On-Demand) and the capability to change the attributes of the RI as long as the exchange results in the creation of Reserved Instances of equal or greater value. Like Standard RIs, Convertible RIs are best suited for steady-state usage.
  • Scheduled RIs: These are available to launch within the time windows you reserve. This option allows you to match your capacity reservation to a predictable recurring schedule that only requires a fraction of a day, a week, or a month.

Regional Benefit
Reserved Instances (either Standard or Convertible) can now be set to automatically apply across all Availability Zones in a region. The regional benefit automatically applies your RIs to instances across all Availability Zones in a region, broadening the application of your RI discounts. When this benefit is used, capacity is not reserved since the selection of an Availability Zone is required to provide a capacity reservation. In dynamic environments where you frequently launch, use, and then terminate instances this new benefit will expand your options and reduce the amount of time you spend seeking optimal alignment between your RIs and your instances. In horizontally scaled architectures using instances launched via Auto Scaling and connected via Elastic Load Balancing, this new benefit can be of considerable value.

What does this mean for RI Customers?

Making sense of all the different types of Reserved Instance types and combinations can be daunting. The simplest way to explain the new changes is to know that it only applies to Standard and Convertible RIs. You can now trade “capacity reservation” for flexibility across multiple availability zones for purchased RIs. If you take advantage of the new Regional Benefit keep in mind that you are no longer “guaranteed” capacity for the RIs that you have purchased. For most, it seems out of the realm of possibility for instances to be out of stock, but consider a situation where an availability zone was to go down. DevOps teams have built-in mechanisms to compensate for this and will automatically provision new instances in the AZs that remain online. In this type of scenario, it’s easy to see how capacity could quickly evaporate for AWS clients. This is why it is important to have automation in place to ensure that you can support heterogeneous clusters to ensure that you can make use of whatever capacity is available at any given time. This applies to RIs, On-Demand instances, and of course Spot instances.


Combined with Spotinst ECO RI lifecycle management you can rest assured that your AWS spend is fully optimized. Learn more about Spotinst ECO on our website here:

To learn more about Regional Reserved Instances you can go to the AWS announcement here.