Accessing reservation recommendations

If you enable Cost Explorer, you automatically get Amazon EC2, Amazon RDS, ElastiCache, OpenSearch Service, Amazon Redshift, Amazon MemoryDB, and Amazon DynamoDB purchase recommendations that could help reduce your costs. Reservations provide a discounted hourly rate (up to 75%) compared to On-Demand or provisioned capacity pricing. Cost Explorer generates your reservation recommendations using the following process:

For example, Cost Explorer automatically aggregates your Amazon EC2 Linux, shared tenancy, and c4 family usage in the US West (Oregon) Region and recommends that you buy size-flexible regional RIs to apply to the c4 family usage. Cost Explorer recommends the smallest size instance in an instance family. This makes it easier to purchase a size-flexible RI. Cost Explorer also shows the equal number of normalized units so that you can purchase any instance size that you want. For this example, your RI recommendation would be for c4.large because that is the smallest size instance in the c4 instance family.

Cost Explorer recommendations are based on a single account or organization usage of the past seven, 30, or 60 days. Cost Explorer uses On-Demand instance usage during the selected look-back period to generate recommendations. All other usage in the look-back period that are covered by features such as RI, SPOT, and Savings Plans aren't included. Amazon EC2, ElastiCache, OpenSearch Service, Amazon Redshift, Amazon MemoryDB, and Amazon DynamoDB recommendations are for reservations scoped to Region, not Availability Zones, and your estimated savings reflects the application of those reservations to your usage. Amazon RDS recommendations are scoped to either Single-AZ or Multi-AZ RIs. Cost Explorer updates your recommendations at least once every 24 hours.

Linked accounts can only see recommendations if they have the relevant permissions. Linked accounts need permissions to view Cost Explorer and permissions to view recommendations. For more information, see Viewing reservation recommendations.

RI recommendations for size-flexible RIs

Cost Explorer also considers the benefits of size-flexible regional RIs when generating your RI purchase recommendations. Size-flexible regional RIs help maximize your estimated savings across eligible instance families in your recommendations. AWS uses the concept of normalized units to compare the various sizes within an instance family. Cost Explorer uses the smallest normalization factor to represent the instance type that it recommends. For more information, see Instance size flexibility in the Amazon Elastic Compute Cloud User Guide.

For example, let’s say you own an EC2 RI for a c4.8xlarge. This RI applies to any usage of a Linux/Unix c4 instance with shared tenancy in the same region as the RI, such as the following instances:

It also includes combinations of EC2 usage, such as one c4.4xlarge and eight c4.large instances.

If you own an RI that is smaller than the instance that you're running, you are charged the prorated, On-Demand price for the excess. This means that you could buy an RI for a c4.4xlarge, use a c4.4xlarge instance most of the time, but occasionally scale up to a c4.8xlarge instance. Some of your c4.8xlarge usage is covered by the purchased RI, and the rest is charged at On-Demand prices. For more information, see How Reserved Instance discounts are applied in the Amazon Elastic Compute Cloud User Guide.

Viewing reservation recommendations

Linked accounts need the following permissions to view recommendations:

For more information, see Using identity-based policies (IAM policies) for AWS Cost Management.

Understanding reservation recommendations

The Reservations Recommendations page shows you your estimated potential savings, your reservation purchase recommendations, and the parameters that Cost Explorer used to create your recommendations. You can change the parameters to get recommendations that might match your use case more closely.

The Recommendations page shows you the following three numbers:

These numbers provide you with a rough estimate of how much you could potentially save by buying more reservations. You can recalculate these numbers for a different use case using the following Recommendation parameters:

At the bottom of the page are tabs with some of your savings estimates. The All accounts tab enables you to see the recommendations based on the combined usage across your entire organization, and the Individual accounts tab enables you to see recommendations that Cost Explorer generated on a per-linked-account basis. The table on each tab shows the different purchase recommendations and details about the recommendations. If you want to see the usage that Cost Explorer based a recommendation on, choose the View associated usage link in the recommendation details. This takes you to a report that shows the exact parameters that Cost Explorer used to generate your recommendation. The report also shows your costs and associated usage grouped by Purchase option, so that you can view the On-Demand Instance usage that your recommendation is based on.

You can sort your recommendations by Monthly estimated savings, Upfront RI cost, Purchase recommendation, or Instance type.

Modifying reservation recommendations

You can change the information that Cost Explorer uses when it creates your recommendations, and you can also change the types of recommendations that you want. This allows you to see recommendations for the reservations that work best for you, such as All upfront reservations with a one-year term, based on your last 30 days of usage.

Saving reservation recommendations

You can save reservation recommendations as a CSV file.

The CSV file contains the following columns.

Using reservation recommendations

To purchase the recommended reservations, go to the purchase page in a service console. You can also save a CSV file of your recommendations and purchase the reservations at a later date.