Amazon EC2 Capacity Reservations allow you to reserve compute capacity for your Amazon EC2 instances in a specific Availability Zone for any duration. If you have strict capacity requirements for current or future business-critical workloads that require a certain level of long or short-term capacity assurance, we recommend that you create a Capacity Reservation to help ensure that you always have access to Amazon EC2 capacity when you need it, for as long as you need it.
You can create a Capacity Reservation at any time, and you can choose when it starts. You can request a Capacity Reservation for immediate use or you can request a Capacity Reservation for a future date.
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If you request a Capacity Reservation for immediate use, the Capacity Reservation becomes available for use immediately and there is no term commitment. You can modify the Capacity Reservation at any time, and you can cancel it at any time to release the reserved capacity and to stop incurring changes.
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If you request a future-dated Capacity Reservation, you specify the future date at which you need the Capacity Reservation to become available for use. You must also specify a commitment duration for which you commit to keeping the requested capacity in your account after the specified date. At the requested date and time, the Capacity Reservation becomes available for use and the commitment duration starts. During the commitment duration, you can't decrease the instance count or commitment duration below your initial commitment, or cancel the Capacity Reservation. After the commitment duration elapses, you can modify the Capacity Reservation in any way or cancel it if you no longer need it.
Capacity Reservations can only be used by instances that match their attributes. By default, Capacity Reservations automatically match new instances and running instances that have matching attributes (instance type, platform, Availability Zone, and tenancy). This means that any instance with matching attributes automatically runs in the Capacity Reservation. However, you can also target a Capacity Reservation for specific workloads. This allows you to explicitly control which instances are allowed to run in that reserved capacity. You can also specify that instances will only run in a Capacity Reservation or Capacity Reservation resource group.
Important
Future-dated Capacity Reservations are for helping you launch and cover incremental instances, and not to cover existing running instances. If you need to cover existing running instances, use Capacity Reservations that start immediately instead.
All Amazon EC2 instances, launched by you (non-managed instances) or on your behalf by an AWS service (managed instances), are eligible to run in a Capacity Reservation, if they have matching attributes (instance type, platform, Availability Zone, and tenancy). This is particularly true for open Capacity Reservations, which automatically match with any running instances that have matching attributes. For example, managed instances launched on your behalf by the following services are eligible to run in Capacity Reservations that you create and manage.
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Amazon EC2 Auto Scaling
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Amazon EMR
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AWS ParallelCluster
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Amazon EKS
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Amazon ECS
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AWS Batch
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AWS Elastic Beanstalk
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Amazon SageMaker AI
Contents
Differences between Capacity Reservations, Reserved Instances,
and Savings Plans
The following table highlights key differences between Capacity Reservations, Reserved Instances, and Savings Plans:
| Capacity Reservations | Zonal Reserved Instances | Regional Reserved Instances | Savings Plans | |
|---|---|---|---|---|
| Term | No commitment required for immediate-use Capacity Reservations. They can be created, modified, and canceled as needed. With future-dated Capacity Reservations, you specify a commitment duration for which you commit to keeping the capacity in your account. After the commitment duration elapses, you can cancel the Capacity Reservation at any time. |
Requires a fixed one-year or three-year commitment | ||
| Capacity benefit | Capacity reserved in a specific Availability Zone. | No capacity reserved. | ||
| Billing discount | No billing discount. † | Provides a billing discount. | ||
| Instance Limits | Your On-Demand Instance limits per Region apply. | Default is 20 per Availability Zone. You can request a limit increase. | Default is 20 per Region. You can request a limit increase. | No limit. |
† You can combine Capacity Reservations with Savings Plans or Regional Reserved Instances to receive a discount.
For more information, see the following:
Supported platforms
You must create the Capacity Reservation with the correct platform to ensure that it properly matches
with your instances. Capacity Reservations support the following values for platform:
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Linux/UNIX
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Linux with SQL Server Standard
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Linux with SQL Server Web
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Linux with SQL Server Enterprise
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SUSE Linux
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Red Hat Enterprise Linux
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RHEL with SQL Server Standard
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RHEL with SQL Server Enterprise
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RHEL with SQL Server Web
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RHEL with HA
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RHEL with HA and SQL Server Standard
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RHEL with HA and SQL Server Enterprise
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Ubuntu Pro
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Windows
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Windows with SQL Server
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Windows with SQL Server Web
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Windows with SQL Server Standard
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Windows with SQL Server Enterprise
To ensure that an instance runs in a specific Capacity Reservation, the platform of the Capacity Reservation must match the platform of the AMI used to launch the instance. For Linux AMIs, it is important to check whether the AMI platform uses the general value Linux/UNIX or a more specific value like SUSE Linux.
To check the AMI platform using the console
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Open the Amazon EC2 console at https://console.aws.amazon.com/ec2/
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In the navigation pane, choose AMIs.
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Select the AMI.
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On the Details tab, note the value of Platform details.
To check the AMI platform using the AWS CLI
Use the describe-imagesPlatformDetails.
aws ec2 describe-images --image-id ami-0acefc55c3EXAMPLE --query Images[*].PlatformDetails
The following is example output.
[
"Linux/UNIX"
]Quotas
The number of instances for which you are allowed to reserve capacity is based on your account's On-Demand Instance quota. You can reserve capacity for as many instances as that quota allows, minus the number of instances that are already running.
Capacity Reservations in the assessing, scheduled, pending ,
active, and delayed state count towards your On-Demand Instance
quota.
Limitations
Before you create Capacity Reservations, take note of the following limitations and restrictions.
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Active and unused Capacity Reservations count toward your On-Demand Instance limits.
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Capacity Reservations are not transferable from one AWS account to another. However, you can share Capacity Reservations with other AWS accounts. For more information, see Shared Capacity Reservations.
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Zonal Reserved Instance billing discounts do not apply to Capacity Reservations.
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Capacity Reservations can be created in cluster placement groups. Spread and partition placement groups are not supported.
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Capacity Reservations can't be used with Dedicated Hosts. Capacity Reservations can be used with Dedicated Instances.
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[Windows instances] Capacity Reservations can't be used with Bring Your Own License (BYOL).
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Capacity Reservations do not ensure that a hibernated instance can resume after you try to start it.
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You can request future-dated Capacity Reservations for an instance count with a minimum of 100 vCPUs. For example, if you request a future-dated Capacity Reservation for
m5.xlargeinstances, you must request at least 25 instances (25 * m5.xlarge = 100 vCPUs). -
You can request future-dated Capacity Reservations for instance types in the C, I, M, R, or T instance families only.
