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You may find yourself sitting here thinking about how you’re missing out on the full benefit of Reserved Instances (RIs). Maybe you’ve been holding off on buying RIs because your constantly changing workloads are impossible to predict. Or maybe you have purchased RIs, but your reservations underutilized, so you end up paying On-Demand prices for newly spun up instances.
RI modifications are the answer to keeping up with your fast-growing infrastructure.
How Modifications Work
AWS allows you to modify your existing reservations at no cost, allowing you to align the cost and capacity benefit with your On-Demand usage. Two common ways to modify reservations are moving them to a new Availability Zone within the same Region or splitting/merging reservations within the same instance family.
Moving RIs to New Availability Zones
Modifying your RI to cover a different Availability Zone is the easiest way to align capacity with your On-Demand usage. For example, if you are spinning down your On-Demand instances once you’ve made a reservation purchase only to spin them up in a different Availability Zone in the same region, you can easily modify your RIs to cover the usage in this new region as well.
Splits and Merges
Splits and merges can be more complicated to manage. For example, an m4.xlarge reservation could be split to make 2 m4.large reservations. The reverse of this is merging where 2 m4.large reservations could be merged to make 1 m4.xlarge reservation. Within an instance family, RIs can be merged and split in a variety of ways, all at no cost.
How to Make Modifications
Without visibility into the utilization of your reservations and your On-Demand usage, RI modifications can be incredibly time consuming and almost impossible to determine on your own. Before you make a modification, you will have to determine the number of instance hours and reservation hours per Availability Zone across all accounts within your consolidated bill for an analysis period. The analysis also needs to determine instance execution hours and RI usage hours per operating system, Availability Zone , instance-type, and tenancy, which gets very complicated for large environments. Then, you will need to manually modify each reservation in the AWS console and change the Availability Zone or execute the split/merge.
A Better Way To Approach RI Modifications
Luckily, CloudHealth’s RI Modifier tool will analyze your On-Demand usage and RI utilization for an interval period to determine opportunities for modifications and their associated cost savings. Not only will CloudHealth show you the opportunities available for modifications, but, with our unique automated actions and workflows, you can modify directly from our platform, or you can set up policies to automatically make reservation modifications when they will save you money. This saves you time and means you can avoid the hassle of going into the AWS console to make these changes. Expanding the opportunities found in Cloudhealth will show the reservation utilization and the potential utilization if modified to the recommended size or Availability Zone.