After you purchase reserved instances, you make commitments to using pay-as-you-go instances for a period of time. Reserved instances can be used to offset bills of pay-as-you-go instances only when they match the pay-as-you-go instances. If you do not have any pay-as-you-go instances in your account, the reserved instances are idle and continue to be charged. This topic describes the matching rules of reserved instances and provides some examples.
Matching rules
The match between reserved instances and pay-as-you-go instances cannot be manually managed. After you purchase a reserved instance, the reserved instance automatically matches one or more pay-as-you-go instances that have some attributes within the term. After the reserved instance is matched, it checks for eligible pay-as-you-go bills on an hourly basis and deducts fees based on its computing power. You can view pay-as-you-go instances that match the reserved instance. For more information, see View matched pay-as-you-go instances.
The matching conditions of a regional reserved instance are different from those of a zonal reserved instance. The following table describes the attributes that determine the match between reserved instances and pay-as-you-go instances.
| Attribute | Regional reserved instance | Zonal reserved instance |
|---|---|---|
| Region and zone | A regional reserved instance can match one or more pay-as-you-go instances across zones within a specific region. | A zonal reserved instance can match one or more pay-as-you-go instances only in the same zone. |
| Instance type | The following section describes the instance size flexibility and resource reservation status:
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The following section describes the instance size flexibility and resource reservation status:
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| Operating system | A regional reserved instance can match only pay-as-you-go instances that have the same operating system. | A zonal reserved instance can match only one or more pay-as-you-go instances that have the same operating system. |
Examples of regional reserved instances
Regional reserved instances and pay-as-you-go instances must meet the following requirements to match:
- They must reside within the same region.
- They must use instances types that belong to the same instance family. Within the same instance family, regional reserved instances of small instance types can match pay-as-you-go instances of large instance types or regional reserved instances of large instance types can match pay-as-you-go instances of small instance types.
Note You can evaluate the usage of reserved instances based on the computing power when the instance sizes of the reserved instance and the pay-as-you-go instance are different.
- They must run the same operating system.
The following table describes examples of regional reserved instances.
| Scenario | Pay-as-you-go instance | Regional reserved instance | How bills are offset |
|---|---|---|---|
| Regional reserved instances of small instance types match pay-as-you-go instances of large instance types | You have a pay-as-you-go instance that has the following configurations:
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You have two active regional reserved instances that have the following attributes:
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The following section describes the normalization factors:
Comparison between the delivered and consumed computing powers:
Therefore, one reserved instance offsets 50% of the pay-as-you-go instance bills per hour, and two reserved instances offset 100% of the pay-as-you-go instance bills per hour. |
| Regional reserved instance of large instance types match pay-as-you-go instances of small instance types | You have six pay-as-you-go instances.
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You have two active regional reserved instances.
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The following section describes the normalization factors:
Comparison between the delivered and consumed computing powers:
Therefore, the two reserved instances offset 100% of bills of the six pay-as-you-go instances per hour.
Note The pay-as-you-go instances belong to two zones. However, the regional reserved instances support the zone flexibility and can offset bills of pay-as-you-go instances across zones.
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| Failed to match | You have two pay-as-you-go instances.
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You have two active regional reserved instances.
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The reserved instances failed to match the pay-as-you-go instances due to the following causes:
Therefore, the reserved instances remain idle and continue to be charged. The bills of pay-as-you-go instances are paid by account balance. |
Examples of zonal reserved instances
Zonal reserved instances and pay-as-you-go instances must meet the following requirements to match:
- They must reside within the same region and zone.
- They must use instance types that belong to the same instance family and have the same size.
- They must run the same operating system.
The following table describes examples of zonal reserved instances.
| Scenario | Pay-as-you-go instance | Zonal reserved instance | How bills are offset |
|---|---|---|---|
| Matched | You have five pay-as-you-go instances that have the following configurations:
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You have an active zonal reserved instance that has the following attributes:
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The reserved instance matches the pay-as-you-go instances. The reserved instance offsets 100% of bills of the five pay-as-you-go instances per hour. |
| Resource reservation | You have no pay-as-you-go instances. | You have an active zonal reserved instance that has the following attributes:
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The reserved instance is idle and continues to be charged. However, 10 pay-as-you-go instances of the ecs.g5.2xlarge instance type are reserved for you within the term of the reserved instance. This ensures that you can create pay-as-you-go instances anytime in Qingdao Zone B. |
| Failed to match | You have two pay-as-you-go instances.
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You have two active zonal reserved instances.
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The reserved instances failed to match the pay-as-you-go instances due to the following causes:
Therefore, the reserved instances remain idle and continue to be charged. The bills of pay-as-you-go instances are paid by account balance. |
Match between a single reserved instance and multiple pay-as-you-go instances
A single regional or zonal reserved instance can match multiple pay-as-you-go instances. However, you cannot shorten the term of a reserved instance to deliver more computing power.
The following table describes an example that involves six pay-as-you-go instances and an active reserved instance.
| Six pay-as-you-go instances | An active reserved instance |
|---|---|
The following section describes the configurations of each pay-as-you-go instance:
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The following section describes the attributes of the reserved instance:
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The six pay-as-you-go instances all match the reserved instance. The following table describes examples of how the reserved instances offset bills of the pay-as-you-go instances based on how long each pay-as-you-go instance exists.
| Six pay-as-you-go instances | A reserved instance | How bills are offset |
|---|---|---|
The following section describes the consumed computing power:
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The following section describes the delivered computing power: Computing power delivered by the reserved instance per hour: 24 (1 instance × 24) |
The computing power delivered by the reserved instance is equal to that consumed by a pay-as-you-go instance. The reserved instance offsets the bills of a pay-as-you-go instance randomly. You cannot shorten the term of the reserved instance to two months to offset bills of the six pay-as-you-go instances at the same time. |
The following section describes the consumed computing power:
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The following section describes the delivered computing power: Computing power delivered by the reserved instance per hour: 24 (1 instance × 24) |
The computing power delivered by the reserved instance is equal to that consumed by the six pay-as-you-go instances. The reserved instance offsets bills of the six pay-as-you-go instances. |
The following section describes the consumed computing power:
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The following section describes the delivered computing power: Computing power delivered by the reserved instance per hour: 24 (1 instance × 24) |
The computing power delivered by the reserved instance is less than that consumed by the six pay-as-you-go instances. The reserved instance offsets bills of the six pay-as-you-go instances for an hour. The deducted amount of each pay-as-you-go instance is random. |