The Reserved page shows cost saving opportunities through the purchase of EC2 Reserved Instances (RIs), as well as how completely the organization's EC2 consumption is covered by those RIs. Consider AWS's EC2 Reserved Instances documentation to gain a thorough understanding of what RIs are and how they can provide cost savings.
Stax provides, on the Reserved page, the following information to help you understand your EC2 Reserved Instances position:
The What EC2 usage is covered by RIs? panel shows an aggregate of the normalized virtual CPU (vCPU) hours for all EC2 instances in the environment. This allows Stax to represent instances of all sizes in the same graph. The normalized vCPU hours value is calculated by taking the amount of time an instance was running during a given period, then multiplying that by the number of vCPU cores present in the instance type. This chart is not a representation of cost or cost savings, but rather a representation of volume of compute and its coverage by RIs.
The Where to focus your savings efforts? graph represents the Reserved Instances types that may be considered for purchase. It breaks down recommendations to show the potential RI coverage on the y-axis (vertical axis), and RI cost on the x-axis (horizontal axis). Put simply, Stax recommends you purchase the RI with the largest circle on the graph. This, of course, does not consider your organization's unique requirements and position, and it does not represent any savings already made as a result of Savings Plans or other cost saving measures.
The What RIs to purchase to reduce spend table provides a list of recommended Reserved Instances purchases. This is retrieved from the AWS Reserved Instances API. It shows the current Reserved Instances coverage for a given instance types and families (e.g. m5.2xlarge and r5 family).
In all cases, it is crucial to apply business knowledge and understanding to the recommendations on the Reserved page before making any purchases.
Considerations
- In many cases, Savings Plans provides a more comprehensive and financially favourable approach to usage commitments in AWS. Consider your use case to determine whether a Savings Plan purchase would be more effective than Reserved Instances
- Reserved Instances can be purchased at either the AWS Organization's management account or at an individual account within the Organization. RIs applied to the management account cannot be applied to specific instances or AWS accounts within the organization. Consider how this may impact any chargeback/showback models when purchasing Reserved Instances
- Recommendations presented in Stax refer to Standard RIs over a 1-year term with the No Upfront payment option