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Elastic Compute Service

Reserved Instances

Overview of Reserved Instances

Reserved Instances (RI) is an instance voucher with deduction and reservation capabilities. You can use it to deduct the bills for compute resources (vCPU, GPU, and memory) required by pay-as-you-go instances (excluding spot instances). You can also use it to reserve resources to ensure stable supply.

If you combine RI with pay-as-you-go instances, it can offer significant price advantages, including discounts, compared to bills from pay-as-you-go instances.

Unlike subscription instances, RI provides computing power upon purchase instead of specific instances. Without being associated with a specific instance, pay-as-you-go instances that meet the requirements can be matched with RI, which is more flexible than subscription instances.

Applicable scenarios

For stable elastic scenarios, we recommend that you use RI to significantly reduce your costs.

Automated operations: In auto scaling (AS) and other automated operation scenarios, RI can help you automatically create or delete instances. RI can adjust resource types and distributions based on factors such as business changes, peaks, and troughs.

Elastic scenarios: The total resource amount remains relatively stable, but resources must be used flexibly based on business needs. In such scenarios, you can use RI to further reduce costs and improve efficiency.

Resource locking: For critical elastic workloads or in scenarios with tight resource supply, RI can help you lock resources in advance to avoid availability risks.

Concepts

Term	Description
RI	A deduction coupon can not be used alone and must be used with pay-as-you-go instances. RIs can be divided into regional RI and zonal RI.
Zonal RI	Resource reservation is supported. In the same availability zone, zonal RI can deduct pay-as-you-go instances that are the same type as that specified in RI.
Regional RIs	Resource reservation is not supported. But for all pay-as-you-go instances of the same instance family in the same region, you can flexibly deduct bills with regional RIs.
resource reservation	If no instances are available for deduction by zonal RI, the system reserves instance resources for you with the same type and instance quantity in the availability zone, as specified in the RI.
Modifies RIs	It means that you can change the attributes of RI, such as number, availability zone, instance type, instance number. For more details, refer to Modifying Reserved Instances.
Normalization factor	It serves to abstractly represent the computing power of instances with different types. For details, refer to Viewing normalization factor.
Computing power	It refers to the total computing power that RIs can offset. One RI can only offset resource usage equal to its total computing power per hour. Computing power=normalization factor * instance quantity

RI types

The platform provides regional RI and zonal RI. The comparison is as follows:

tip

Regional RI is currently in Beta. If you need a trial, please contact your account manager to apply.

Item	Zonal RI	Regional RIs
Resource reservation capability	Resource reservation is supported. Zonal RI ensures that you can create pay-as-you-go instances of the specified types and quantity within the validity period of RI.	Resource reservation is not supported.
Availability zone flexibility	Zonal RI supports matching with pay-as-you-go instances in the same availability zone as the RI specified zone.	Regional RI allows matching with pay-as-you-go instances in different availability zones within the same region.
Instance type flexibility	Pay-as-you-go instances of the same type as that specified in RI can be matched.	Regional RI can flexibly offset pay-as-you-go instances within the same region that belong to the same instance family as the instance family specified in RI.

Considerations

About instance quantity:

The number of instances that an RI can offset or reserve is determined by the number of vCPUs in the instance. By default, in a single availability zone, the total number of vCPUs that can be offset by all RIs owned by an account is no more than 200. To increase your vCPU quota, go to the Quota center. Learn more.

About instance type:

For details of instance families that support RI, refer to Buying Reserved instances.

For details of RIs that do not support changing instance types, refer to Modifying Reserved Instances. And for deduction or reservation of these instance types, you can only purchase zonal RIs.

Regional RI and zonal RI support mutual conversion. For specific actions, refer to Change Reserved Instances (RI) attribute.

Lifecycle

During the lifecycle, some status of RI are predefined, as listed in the following table:

Status	State attribute	State description
Creating	Intermediate state	The status before RI enters In effect status after you purchase RI. The status of newly generated target RI after you make the change.
Enabled	Stable state	Normal status. You can use RI to deduct pay-as-you-go instances bills.
During change	Intermediate state	The status of original RI after you change it.
Invalid	Stable state	If one RI is expired or canceled, it enters the Expired status. The status of original RI after you change it.

Feature	Documentation
Billing methods/deduction rules/unsubscription	RI
Purchasing RI	Purchasing RI
Matching rules for RI and pay-as-you-go instances	Reserved Instances (RI) match rules Viewing normalization factor
Modify RI types	Modify the availability zone of RI
Split one RI with large computing power into multiple RIs with small computing power	Split RI
Merge multiple RIs with small computing power into one RI with large computing power	Merge RI
Renewing Reserved instances	Renewing Reserved instances