Enabling and Purchasing a Reserved Instance

A reserved instance (RI) is not an actual instance, but a billing discount that can be applied to pay-per-use ECSs in your account. When the attributes of your pay-per-use ECSs match those of an RI, the RI's discount rate automatically applies to your ECSs.

RIs are suitable for scenarios where the resource usage duration can be predicted. Billing automatically applies your RI's discounted rate when attributes of your ECS usage match attributes of an RI.

For more information about RIs, see Reserved Instance Overview.
For instructions about how to modify an RI, see Modifying RI Attributes.

Notes and Constraints

The quota for the number of RIs that you can purchase in the current region is displayed in the upper left area of the Reserved Instance page. The quota for the number of RIs that can be purchased by a user in each region is 20.
The quota for the number of RIs is automatically reset every month.
The remaining quota for the number of RIs (Remaining quota = Total quota – Used quota) is reduced only after more RIs are purchased. It will not be changed if RIs are modified, split, combined, or unsubscribed.

Enabling RIs

Before purchasing an RI, contact customer service to apply for the required permissions.

Purchasing an RI

Log in to the management console.
Under Computing, click Elastic Cloud Server.
In the navigation pane on the left, choose Reserved Instance.
Click Buy RI.
The Buy RI page is displayed.
Confirm the region.
If the RIs in the selected region do not meet your requirements, select another region.
Select an RI type.
The cloud platform provides various RI types for you to choose from based on your application scenarios.

Filter for RI specifications.

Set flavor, OS, term, offering class, and payment option to search for the target RI specifications.

Table 1 shows specifications parameters.

**Table 1** RI attributes
Parameter	Description
Region	Regional RI: indicates an RI purchased in a region, without an AZ specified. Capacity reservations are not supported for regional RIs.
Flavor	When purchasing a regional RI, ensure that the ECS series and vCPU/memory ratio specified in the RI are the same as those of the target pay-per-use ECS. NOTE: After an RI is purchased, its flavor cannot be directly changed, but you can split or combine it. For details, see Modifying RI Attributes.
OS	The OS of the ECS to be bought, which must match the OS specified in your RI. For example, if you want to use a Linux RI, select a Linux public or private image when purchasing an ECS.
Term	The service duration of an RI. A year is defined as 31,536,000 seconds (365 days).
Offering Class	Standard: Certain attributes, such as the ECS size can be modified during the term. However, the ECS type cannot be changed.
Payment Option	No upfront

Select specifications.
The cloud platform provides various RI types for you to choose from based on your application scenarios. On the Buy RI page, view released RI types and specifications.

Effective Rate: amortized hourly costs of the RI, which is equivalent to the total cost (including any upfront payment) of the RI over the entire term divided by the total number of hours over the entire term. (Effective rate = Total cost of the RI/Entire term of the RI)

Upfront Price: fee that needs to be paid before you purchase an RI.

Hourly Rate: amortized hourly costs of the RI, which is equivalent to the difference between the total cost of the RI and the upfront payment divided by the total number of hours over the entire term (Hourly rate = Total cost of the RI – Upfront payment/Entire term of the RI)
Specify an RI name.
The name can be customized. It can contain 1 to 128 characters, which can only be letters, digits, underscores (_), and hyphens (-).
Set the number of RIs to be purchased.
- Quantity: The system displays the number of RIs that you can purchase.
- Total Normalization Factors: measures the ECS size flexibility. The value is determined based on the specifications of the RI to be purchased.
Click Next.
To learn more about the price, click Pricing details.
On the page for you to confirm RI specifications, view details and submit the request.
After verifying the configurations and price, click Submit and pay for the order as prompted.
Return to the RI list as prompted and view the purchased RI.

Follow-up Operations

Purchase a pay-per-use ECS that matches an RI.
Locate the target RI and click Buy ECS in the Operation column. The system automatically switches to the page for purchasing ECSs, and the specifications of the ECSs selected by default are the same as those specified in the RI.
- If the OS of the target ECS does not match the OS specified in the RI, or the target ECS is not billed on a pay-per-use basis, the RI cannot be used. When the attributes of the ECS match those of the RI, including the ECS series and vCPU/memory ratio, the ECS automatically benefits from the billing discount offered by the RI.
Check the usage of RIs.
On the Reserved Instance page, click the name of the target RI. In the lower part of the RI details page, view the usage of the RI.

As shown in Figure 1, the horizontal coordinate indicates the number of in-service days, and the vertical coordinate indicates the usage of RI on the current day. Click the chart to view the RI usage in the selected time period on the current day.
Figure 1 Viewing RI usage