A reserved instance is a discount coupon that can be applied automatically 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 and pay-as-you-go instances provides similar cost-effectiveness to subscription instances but with a higher degree of flexibility.

Comparison between reserved instances, pay-as-you-go instances, and subscription instances

The following table lists differences 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 used independently. They must match pay-as-you-go instances to provide billing discounts. Pay-as-you-go instances can be used independently. 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 used independently. They can be used as simple web servers, or used in combination with other Alibaba Cloud services to deliver powerful solutions.

Scenarios

The following table lists scenarios where a combination of reserved and pay-as-you-go instances is the optimal solution.
Scenario Combination of reserved 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 ECS instances in the original zone and create ECS instances in zones of the destination region. A combination of reserved and pay-as-you-go instances has the following benefits:
  • After you purchase reserved instances, you make commitments to using pay-as-you-go instances for a certain period of time. Reserved instances provide significant discounts compared with pay-as-you-go pricing.
  • Reserved instances that you purchase deliver computing power instead of instances. Reserved instances can match pay-as-you-go instances that meet the matching requirements, and are more flexible than subscription instances.
  • You can split or merge reserved instances to offset bills for pay-as-you-go instances of different instance types.
  • You can modify the zone of a reserved instance anytime. A regional reserved instance can be used to offset bills of pay-as-you-go instances across zones.
  • You can pay by hour by selecting the partial upfront or no upfront payment option to avoid financial pressure caused by one-time payment.
The unit prices of pay-as-you-go instances are higher than those of subscription instances. You may fail to create pay-as-you-go instances if resources are insufficient. However, pay-as-you-go instances are easier to manage. For example, after you configure automated O&M, ECS instances are automatically created and released. No manual refunds are involved after ECS instances are released. Pay-as-you-go instances can be used together with Auto Scaling. Bills are associated with ECS instances. You may need to pay service fees when you apply for refunds.
During automated O&M, the number of ECS instances needs to be automatically adjusted. Refunds must be implemented manually.
You use Auto Scaling to manage ECS instances and own 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 ECS 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.

Attributes

The following figure shows the key attributes of a reserved instance.Key attributes of a reserved instance
The following table describes the key attributes of the preceding reserved instance.
Section Attribute Description
Instance type The following instance families support reserved instances:
  • Compute optimized instance families: c6e, c6, c5, ic5, and sn1ne
  • General purpose instance families: g6e, g6, g5, and sn2ne
  • Memory optimized instance families: r6e, r6, r5, and se1ne
  • Instance families with local SSDs: i2 and i2g
  • Instance families with high clock speed: hfc6, hfc5, hfg6, hfg5, and hfr6
  • Compute optimized instance families with GPU capabilities: gn6i and gn6e
  • ECS Bare Metal Instance families: ebmc6, ebmg6, ebmr6, ebmhfc6, ebmhfg6, and ebmhfr6
  • Burstable instance families: t6 and t5
Region and zone You only need 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.

Operating system Reserved instances are classified into Linux and Windows reserved instances. Windows reserved instances can be used to pay for image bills of Windows pay-as-you-go instances.
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.
Instance quantity The instance quantity is used for the following purposes:
  • Calculates the computing power of reserved instances.
  • Specifies the number of reserved resources for zonal reserved instances. For example, in the preceding figure, the instance quantity is two and the used instance type is ecs.r6e.xlarge. This indicates that two pay-as-you-go instances of the ecs.r6e.xlarge instance type are reserved.
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:
  • Evaluates whether the computing power is the same before and after you split or merge reserved instances.
  • Evaluates the usage of a reserved instance when the size of a regional reserved instance is different from that of the matched pay-as-you-go instance.
Term When you purchase a reserved instance, you can choose a term of one year or three years. After you split, merge, and modify reserved instances, terms of the original reserved instances and the new reserved instances are changed accordingly. 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 at the top of 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 bills of pay-as-you-go instances from 13:00 of May 29, 2020 by hour until it expires.

Expired reserved instances cannot continue to offset bills of pay-as-you-go instances. However, the pay-as-you-go instances are not released. This ensures your service continuity.
Note Make sure that your account balance is sufficient to ensure service availability of your pay-as-you-go instances.

Limits

Limited object Limited item Description
Reserved instance Maximum number of reserved instances The maximum number is subject to the type of reserved instances.
  • Maximum number of regional reserved instances: Each account can have up to 20 regional reserved instances in all regions.
  • Maximum number of zonal reserved instances: Each account can have up to 20 zonal reserved instances in each zone.

For example, you can purchase 10 regional reserved instances in China (Hangzhou) and 10 regional reserved instances in China (Qingdao), 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
  • Reserved instances can match only pay-as-you-go instances. Reserved instances cannot match preemptible instances.
  • Reserved instances can be used to offset charges for computing resources of pay-as-you-go instances, and cannot be used to offset charges for network and storage resources of pay-as-you-go instances.
Instance family The gn6i and t5 instance families do not support regional reserved instances, and support only zonal reserved instances. gn6i and t5 reserved instances cannot be split or merged.

Billing

Reserved instances support the All Upfront, Partial Upfront, and No Upfront payment options. Billing standards vary depending on the payment option. For more information, see Reserved instance billing.
Note Whether you can use the No Upfront payment option depends on your ECS instance resource usage. If you want to use the No Upfront payment option, submit a ticket.

References