Maximizing Utilization with Size Flexibility in Regional Reserved Instances - Amazon EC2 Reserved Instances and Other AWS Reservation Models

Maximizing Utilization with Size Flexibility in Regional Reserved Instances

For additional flexibility, all Regional Linux Reserved Instances with shared tenancy apply to all sizes of instances within an instance family and an AWS Region, even if you are using them across multiple accounts via Consolidated Billing. The only attributes that must be matched are the instance type (for example, m4), tenancy (must be default), and platform (must be Linux). All new and existing Reserved Instances are sized according to a normalization factor based on instance size, as follows.

Table 3 – Regional Reserved Instance sizes and normalization factors

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
12xlarge 96
16xlarge 128
24xlarge 192
32xlarge 256

For example, if you have a Reserved Instance for a c4.8xlarge, it applies to any usage of a Linux c4 instance with shared tenancy in the AWS Region, such as:

  • One c4.8xlarge instance

  • Two c4.4xlarge instances

  • Four c4.2xlarge instances

  • Sixteen c4.large instances

It also includes combinations of instances, 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) Region and you have two running t2.small instances in your account in that Region, the billing benefit is applied in full to both instances.

Figure 1 – Two t2.medium instances running in a Region

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.

Figure 2 – One t2.large instance running in a Region

The normalization factor is also applied when modifying Reserved Instances.