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Amazon Elastic Compute Cloud
User Guide for Linux Instances

How Reserved Instances Are Applied

If you purchase a Reserved Instance and you already have a running instance that matches the specifications of the Reserved Instance, the billing benefit is immediately applied. You do not have to restart your instances. If you do not have an eligible running instance, launch an instance and ensure that you match the same criteria that you specified for your Reserved Instance. For more information, see Using Your Reserved Instances.

Reserved Instances apply to usage in the same manner, irrespective of the offering type (Standard or Convertible), and are automatically applied to running On-Demand Instances with matching attributes.

How Zonal Reserved Instances Are Applied

Reserved Instances assigned to a specific Availability Zone provide the Reserved Instance discount to matching instance usage in that Availability Zone. For example, if you purchase two c4.xlarge default tenancy Linux/Unix Standard Reserved Instances in Availability Zone us-east-1a, then up to two c4.xlarge default tenancy Linux/Unix instances running in the Availability Zone us-east-1a can benefit from the Reserved Instance discount. The attributes (tenancy, platform, Availability Zone, instance type, and instance size) of the running instances must match that of the Reserved Instances.

How Regional Reserved Instances Are Applied

Reserved Instances purchased for a region (regional Reserved Instances) provide Availability Zone flexibility—the Reserved Instance discount applies to instance usage in any Availability Zone in that region.

Regional Reserved Instances on the Linux/Unix platform with default tenancy also provide instance size flexibility, where the Reserved Instance discount applies to instance usage within that instance type, regardless of size.

Note

Instance size flexibility does not apply to Reserved Instances that are purchased for a specific Availability Zone, and does not apply to Windows, Windows with SQL Standard, Windows with SQL Server Enterprise, Windows with SQL Server Web, RHEL, and SLES Reserved Instances.

Instance size flexibility is determined by the normalization factor of the instance size. The discount applies either fully or partially to running instances of the same instance type, depending on the instance size of the reservation, in any Availability Zone in the region. The only attributes that must be matched are the instance type, tenancy, and platform.

The table below describes the different sizes within an instance type, and corresponding normalization factor per hour. This scale is used to apply the discounted rate of Reserved Instances to the normalized usage of the instance type.

Instance size Normalization factor

nano

0.25

micro

0.5

small

1

medium

2

large

4

xlarge

8

2xlarge

16

4xlarge

32

8xlarge

64

9xlarge

72

10xlarge

80

16xlarge

128

18xlarge

144

32xlarge

256

For example, a t2.medium instance has a normalization factor of 2. If you purchase a t2.medium default tenancy Amazon Linux/Unix Reserved Instance in the US East (N. Virginia) and you have two running t2.small instances in your account in that region, the billing benefit is applied in full to both instances.


					Applying a Regional Reserved Instance

Or, if you have one t2.large instance running in your account in the US East (N. Virginia) region, the billing benefit is applied to 50% of the usage of the instance.


					Applying a Regional Reserved Instance

Note

The normalization factor is also applied when modifying Reserved Instances. For more information, see Modifying Reserved Instances.

Examples of Applying Reserved Instances

The following scenarios cover the ways in which Reserved Instances are applied.

Example Scenario 1: Reserved Instances in a Single Account

You are running the following On-Demand Instances in account A:

  • 4 x m3.large Linux, default tenancy instances in Availability Zone us-east-1a

  • 2 x m4.xlarge Amazon Linux, default tenancy instances in Availability Zone us-east-1b

  • 1 x c4.xlarge Amazon Linux, default tenancy instances in Availability Zone us-east-1c

You purchase the following Reserved Instances in account A:

  • 4 x m3.large Linux, default tenancy Reserved Instances in Availability Zone us-east-1a (capacity is reserved)

  • 4 x m4.large Amazon Linux, default tenancy Reserved Instances in us-east-1

  • 1 x c4.large Amazon Linux, default tenancy Reserved Instances in us-east-1

The Reserved Instance benefits are applied in the following way:

  • The discount and capacity reservation of the four m3.large Reserved Instances is used by the four m3.large instances because the attributes (instance size, region, platform, tenancy) between them match.

  • The m4.large Reserved Instances provide Availability Zone and instance size flexibility, because they are regional Amazon Linux Reserved Instances with default tenancy.

    An m4.large is equivalent to 4 normalized units/hour.

    You've purchased four m4.large Reserved Instances, and in total, they are equal to 16 normalized units/hour (4x4). Account A has two m4.xlarge instances running, which is equivalent to 16 normalized units/hour (2x8). In this case, the four m4.large Reserved Instances provide the billing benefit to an entire hour of usage of the two m4.xlarge instances.

  • The c4.large Reserved Instance in us-east-1 provides Availability Zone and instance size flexibility, because it is an Amazon Linux Reserved Instance with default tenancy, and applies to the c4.xlarge instance. A c4.large instance is equivalent to 4 normalized units/hour and a c4.xlarge is equivalent to 8 normalized units/hour.

    In this case, the c4.large Reserved Instance provides partial benefit to c4.xlarge usage. This is because the c4.large Reserved Instance is equivalent to 4 normalized units/hour of usage, but the c4.xlarge instance requires 8 normalized units/hour. Therefore, the c4.large Reserved Instance billing discount applies to 50% of c4.xlarge usage. The remaining c4.xlarge usage is charged at the On-Demand rate.

Example Scenario 2: Regional Reserved Instances in Linked Accounts

Reserved Instances are first applied to usage within the purchasing account, followed by qualifying usage in any other account in the organization. For more information, see Reserved Instances and Consolidated Billing. For regional Reserved Instances that offer instance size flexibility, there is no preference to the instance size within a family that the Reserved Instances apply. The Reserved Instance discount is applied to qualifying usage that is detected first by the AWS billing system. The following example may help explain this.

You're running the following On-Demand Instances in account A (the purchasing account):

  • 2 x m4.xlarge Linux, default tenancy instances in Availability Zone us-east-1a

  • 1 x m4.2xlarge Linux, default tenancy instances in Availability Zone us-east-1b

  • 2 x c4.xlarge Linux, default tenancy instances in Availability Zone us-east-1a

  • 1x c4.2xlarge Linux, default tenancy instances in Availability Zone us-east-1b

Another customer is running the following On-Demand Instances in account B—a linked account:

  • 2 x m4.xlarge Linux, default tenancy instances in Availability Zone us-east-1a

You purchase the following Reserved Instances in account A:

  • 4 x m4.xlarge Linux, default tenancy Reserved Instances in us-east-1

  • 2 x c4.xlarge Linux, default tenancy Reserved Instances in us-east-1

The Reserved Instance benefits are applied in the following way:

  • The discount of the four m4.xlarge Reserved Instances is used by the two m4.xlarge instances in account A and the m4.2xlarge instance in account A. All three instances match the attributes (instance family, region, platform, tenancy). There is no capacity reservation.

  • The discount of the two c4.xlarge Reserved Instances can apply to either the two c4.xlarge instances or the c4.2xlarge instance, all of which match the attributes (instance family, region, platform, tenancy), depending on which usage is detected first by the billing system. There is no preference given to a particular instance size. There is no capacity reservation.

Example Scenario 3: Zonal Reserved Instances in a Linked Account

In general, Reserved Instances that are owned by an account are applied first to usage in that account. However, if there are qualifying, unused Reserved Instances for a specific Availability Zone (zonal Reserved Instances) in other accounts in the organization, they are applied to the account before regional Reserved Instances owned by the account. This is done to ensure maximum Reserved Instance utilization and a lower bill. For billing purposes, all the accounts in the organization are treated as one account. The following example may help explain this.

You're running the following On-Demand Instance in account A (the purchasing account):

  • 1 x m4.xlarge Linux, default tenancy instance in Availability Zone us-east-1a

A customer is running the following On-Demand Instance in linked account B:

  • 1 x m4.xlarge Linux, default tenancy instance in Availability Zone us-east-1b

You purchase the following Reserved Instances in account A:

  • 1 x m4.xlarge Linux, default tenancy Reserved Instance in Availability Zone us-east-1

A customer also purchases the following Reserved Instances in linked account C:

  • 1 x m4.xlarge Linux, default tenancy Reserved Instances in Availability Zone us-east-1a

The Reserved Instance benefits are applied in the following way:

  • The discount of the m4.xlarge Reserved Instance owned by account C is applied to the m4.xlarge usage in account A.

  • The discount of the m4.xlarge Reserved Instance owned by account A is applied to the m4.xlarge usage in account B.

  • If the Reserved Instance owned by account A was first applied to the usage in account A, the Reserved Instance owned by account C remains unused and usage in account B is charged at On-Demand rates.

For more information, see Reserved Instances in the Billing and Cost Management Report.