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Amazon Elastic Compute Cloud
User Guide for Linux Instances

Changing the Instance Size of Your Reservations

You can adjust the instance size of your Reserved Instances if you have Amazon Linux reservations in an instance type with multiple sizes. Keep in mind that instance size modifications are allowed only if other attributes—such as region, utilization type, tenancy, product, end date and hour—match and if capacity is available. It is not possible to modify the instance size of Windows Reserved Instances.

Note

Instances are grouped by family (based on storage, or CPU capacity); type (designed for specific use cases); and size. For example, the c4 instance type is in the Compute optimized instance family and is available in multiple sizes. While c3 instances are in the same family, you can't modify c4 instances into c3 instances because they have different hardware specifications. For more information, see Amazon EC2 Instance Types.

The following instances cannot be modified because there are no other sizes available.

  • t1.micro

  • cc1.4xlarge

  • cc2.8xlarge

  • cg1.8xlarge

  • cr1.8xlarge

  • hi1.4xlarge

  • hs1.8xlarge

  • g2.2xlarge

Your request proceeds successfully if the capacity exists and the modification does not change the instance size footprint of your Reserved Instances. Instance size footprints are determined by the normalization factor of the instance type and the number of instances in the reservation. For example, you can divide a reservation for one m1.large instance into four m1.small instances, or you can combine a reservation for four m1.small instances into one m1.large instance. In either case, the instance size footprint of the reservation does not change. However, you cannot change your reservation for two m1.small instances into one m1.large instance because the existing instance size footprint of your current reservation is smaller than the proposed reservation.

Understanding the Instance Size Footprint

Each Reserved Instance has an instance size footprint, which is determined by the normalization factor of the instance type and the number of instances in the reservation. A modification request is not processed if the footprint of the target configuration does not match the size of the original configuration. In the Amazon EC2 console, the footprint is measured in units.

The normalization factor is based on size within the instance type (e.g., the m1 instance family), and is only meaningful within the same instance type; instance types cannot be modified from one type to another. The following table illustrates the normalization factor that applies within an instance type.

Instance sizeNormalization factor

micro

0.5

small

1

medium

2

large

4

xlarge

8

2xlarge

16

4xlarge

32

8xlarge

64

10xlarge

80

To calculate the instance size footprint of a Reserved Instance, multiply the number of instances by the normalization factor. For example, an m1.medium has a normalization factor of 2 so a reservation for four m1.medium instances has a footprint of 8 units.

You can allocate your reservations into different instance sizes across the same instance type as long as the instance size footprint of your reservation remains the same. If you have a reservation covering four m1.medium instances (4 x 2), you can turn it into a reservation for eight m1.small instances (8 x 1). However, you cannot convert a reservation for a single m1.small instance (1 x 1) into a reservation for an m1.large instance (1 x 4). The two footprints are not equal.

For more information, see Amazon EC2 Instance Types.