A reserved instance is a discount coupon that can be automatically applied to one or more pay-as-you-go instances, excluding preemptible instances. A reserved instance can also be used to reserve instance resources. A combination of reserved instances and pay-as-you-go instances provides similar cost-effectiveness to subscription instances but a higher degree of flexibility.
Comparison between reserved instances, pay-as-you-go instances, and subscription instances
|Item||Reserved instance||Pay-as-you-go instance||Subscription instance|
|Form||A discount coupon. Reserved instances are classified into regional and zonal reserved instances.||An instance that uses the pay-as-you-go billing method. A pay-as-you-go instance is equivalent to a virtual machine. For more information, see Pay-as-you-go.||An instance that uses the subscription billing method. A subscription instance is equivalent to a virtual machine. For more information, see Subscription.|
|Purpose||Reserved instances cannot be independently used. They must match pay-as-you-go instances to offset bills.||Pay-as-you-go instances can be independently used. They can be used as simple web servers, or used in combination with other Alibaba Cloud services to deliver powerful solutions.||Subscription instances can be independently used. They can be used as simple web servers, or used in combination with other Alibaba Cloud services to deliver powerful solutions.|
|Scenario||Combination of reserved instances and pay-as-you-go instances||Pay-as-you-go instance||Subscription instance|
|You may need to change the region for your business. You must release Elastic Compute Service (ECS) instances in the original zone and create ECS instances in the zones of the destination region.||A combination of reserved instances and pay-as-you-go instances has the following
||The unit prices of pay-as-you-go instances are higher than those of subscription instances. Pay-as-you-go instances may fail to be created if resources are insufficient. However, pay-as-you-go instances are easier to manage. For example, after you configure automated O&M, instances are automatically created and released. No manual refunds are involved after the instances are released. Pay-as-you-go instances can be used together with Auto Scaling.||Bills are associated with subscription instances. You may need to pay service fees when you apply for refunds.|
|During automated O&M, the number of subscription instances needs to be automatically adjusted.||Refunds must be manually implemented.|
|You use Auto Scaling to manage ECS instances and have a large number of pay-as-you-go instances. You want to lower your costs.||You must manually change pay-as-you instances to subscription instances. This process is inefficient and prone to errors.|
|You want to simplify the operations of managing the lifecycle of subscription instances, such as renewing, releasing, and synchronizing the expiration dates of subscription instances.||You must perform a large number of operations.|
|You want to pay for resources by installments to mitigate financial pressure.||The unit prices are lower. However, one-time payment is required.|
|①||Instance type||The following instance families support reserved instances:
|②||Region and zone||You need only to specify a region for a regional reserved instance. Regional reserved
instances provide zone flexibility and instance size flexibility. You must specify
a region and a zone for a zonal reserved instance. Resource reservation is supported.
The matching conditions are determined by the type of a reserved instance. For more
information, see Match between reserved instances and pay-as-you-go instances.
You can modify the region and zone of a reserved instance after you purchase it. For more information, see Modify a reserved instance.
|③||Operating system||Reserved instances are classified into Linux and Windows reserved instances. Windows reserved instances can be used to offset the image bills of Windows pay-as-you-go instances.|
|④||Normalization factor||A normalization factor indicates the performance level of an instance type and also the computing power. Normalization factors are determined by the number of vCPUs. For information about detailed specifications, see View normalization factors.|
|⑤||Instance quantity||The instance quantity is used for the following purposes:
|⑥||Computing power||Reserved instances deliver computing power in advance. Pay-as-you-go instances consume
the computing power. Computing power of a reserved instance = Normalization factor
of an instance type × Instance quantity.
The computing power is used for the following purposes:
|⑦||Term||You must specify the term when you purchase a reserved instance. After you split,
merge, and modify reserved instances, the terms of the original and new reserved instances
are also changed. For more information, see Split a reserved instance, Merge reserved instances, and Modify a reserved instance.
Note You cannot shorten the term of a reserved instance to deliver more computing power.
A reserved instance takes effect and expires on the hour. For example, you purchased a reserved instance with a term of one year at 13:45 of May 29, 2020. The reserved instance takes effect at 13:00 of May 29, 2020 and expires at 24:00 of May 30, 2021. If you have pay-as-you-go instances that match the reserved instance, the reserved instance is applied to offset the bills of the matching pay-as-you-go instances from 13:00 of May 29, 2020 by hour until it expires.
Expired reserved instances cannot continue to offset the bills of pay-as-you-go instances. However, the pay-as-you-go instances are not released. This ensures continuity of your service.
Note Make sure that your account balance is sufficient to ensure service availability of your pay-as-you-go instances.
|Reserved instance||Maximum number of reserved instances||The maximum number of reserved instances is subject to the type of reserved instances.
For example, you can purchase 10 regional reserved instances in the China (Hangzhou) region and 10 regional reserved instances in the China (Qingdao) region, but the total number of regional reserved instances cannot exceed 20. You can purchase 20 zonal reserved instances in Hangzhou Zone B and 20 zonal reserved instances in Hangzhou Zone H.
If you need more reserved instances, submit a ticket.
|ECS instance||Billing method||
|Instance family||The gn6i and t5 instance families support only zonal reserved instances, not regional reserved instances. gn6i and t5 reserved instances cannot be split or merged.|