Reserved Instance Overview

Concept

A reserved instance (RI) is not an actual instance, but a billing discount that can be applied to the use of pay-per-use ECSs in your account. When the attributes of your pay-per-use ECSs match those of an RI, the RI billing benefit automatically applies to your ECSs. The combination of RIs and pay-per-use billing fully utilizes the flexibility of pay-per-use resources at lower costs.

• A purchased RI is billed, regardless of whether it is used or not.
• RIs are in the open beta test (OBT) phase. You can apply for OBT.

• For instructions about how to purchase an RI, see Enabling and Purchasing a Reserved Instance.
• For instructions about how to modify an RI, see Modifying RI Attributes.

What Is Attribute Mapping Between an RI and a Pay-per-Use ECS?

A regional RI is purchased for a region and without an AZ specified. A zonal RI is purchased for an AZ.

• Attribute matching of a regional RI: The instance series, vCPU/memory ratio, and OS of a regional RI must be the same as those of a pay-per-use ECS.

  If you modify specifications or change the OS of an ECS and still want to enjoy the RI discount, you need to purchase a new RI with the same attributes as the ECS.

• Attribute matching of a zonal RI: The flavor and OS of a zonal RI must be the same as those of a pay-per-use ECS.

  If you modify specifications or change the OS of an ECS and still want to enjoy the RI discount, you need to purchase a new RI with the same attributes as the ECS.

Application Scenarios

If your ECSs will be used in a short term, it is a good practice to use the pay-per-use billing mode. If you plan to use ECSs for one or three years, it is a good practice to use RIs. RIs offer discounts for pay-per-use ECSs with matched attributes.

For example, after you purchase two s3.2xlarge Linux RIs with a one-year term in AZ 1, the billing benefit of the RIs is immediately applied to up to two pay-per-use s3.2xlarge Linux ECSs running in AZ 1.

Working Rules

For example, you have a running pay-per-use ECS in your account. After you purchase an RI that matches the attributes of this ECS, the billing benefit of the RI is automatically applied to your ECS when the RI takes effect. A purchased RI takes effect at the next hour.

Table 2 lists RI attributes. You can purchase your desired RIs based on these attributes.

Zonal RIs

An RI purchased for a specified AZ refers to a zonal RI. It offers a billing discount for the ECSs with the same flavor and OS as the RI in that AZ.

For example, after you purchase two c3.xlarge.2 Linux RIs with a one-year term in an AZ, the RI discounts can be applied to up to two pay-per-use c3.xlarge.2 Linux ECSs running in that AZ.

Regional RIs

Instance size flexibility is applied from the smallest to the largest instance size within the instance series based on the normalization factor. Table 3 describes the instance size within an instance type and corresponding normalization factor per hour.

An ECS automatically benefits from the billing discount offered by a regional RI only when the instance series, vCPU/memory ratio, and OS are the same as those specified in the regional RI.

For example, a regional c3.large.4 RI cannot be used on a c3.large.2 ECS because their vCPU/memory ratios are different.

For example, an s3.large.2 ECS has a normalization factor of 2. You purchase an s3.large.2 Linux RI for the CN-Hong Kong region of Huawei Cloud with a one-year term.

• If you have two running s3.medium.2 pay-per-use Linux ECSs in this region, the billing benefit is fully applied to both ECSs.
  Figure 1 Example RI 1
  
• If you have one running s3.xlarge.2 pay-per-use Linux ECS with a normalization factor of 4 in this region, the billing benefit is applied to 50% of the usage of the ECS.
  Figure 2 Example RI 2
  

Examples

If you have the following pay-per-use ECSs in region A:

• Five s3.large.2 Windows ECSs in AZ 1
• Three m3.xlarge.2 Windows ECSs in AZ 2
• One c3.xlarge.2 Windows ECS in AZ 3

You purchase the following RIs in the same region (region A):

• Five s3.large.2 Windows RIs with a one-year term in AZ 1
• Six m3.large.2 Windows RIs with a one-year term in region A
• One c3.large.2 Windows RI with a one-year term in region A

The RI benefits are applied as follows:

• The discount of the five s3.large.2 zonal RIs is used by the five s3.large.2 ECSs because the attributes (AZ, OS, and ECS type) between the RIs and ECSs match.
• The m3.large.2 regional RIs offer AZ flexibility and instance size flexibility.

  An m3.large.2 RI is equivalent to two normalization factors. The six m3.large.2 regional RIs are equal to 12 normalization factors (6 x 2). There are three running m3.xlarge.2 ECSs in your account, which are equivalent to 12 normalization factors (3 x 4). In this case, the six m3.large.2 regional RIs are equivalent to three m3.xlarge.2 ECSs.

• The c3.large.2 regional RI offers AZ flexibility and instance size flexibility and can be applied to c3.xlarge.2 ECSs.

  A c3.large.2 RI is equivalent to two normalization factors (1 x 2). A c3.xlarge.2 ECS requires an RI with four normalization factors (1 x 4). Therefore, the c3.large.2 RI billing discount applies to 50% of c3.xlarge.2 usage. The remaining c3.xlarge.2 usage is billed at the pay-per-use rate.