Split off capacity from an existing Capacity Reservation
You can split off capacity from an existing Capacity Reservation to create a new reservation. By splitting capacity, you allocate a portion of the original reservation to a specific workload or share it with another Amazon Web Services account. For example, to partially share a Capacity Reservation with another account, you can split off some of the capacity to create a smaller sized Capacity Reservation. The smaller sized Capacity Reservation can then be shared with the other accounts using Amazon Resource Access Manager.
When you split capacity from an existing Capacity Reservation, a new Capacity Reservation is automatically created. The existing reservation will be unchanged, except for the reduced total capacity from the number of instances split off. Instances that are running in the existing Capacity Reservation are not affected. You can split the existing reservation into only one new Capacity Reservation.
The new Capacity Reservation will have the same configuration as the existing Capacity Reservation except for tags. By default, the new Capacity Reservation doesn't have any tags. You can specify new tags during the split operation. The new Capacity Reservation can also be modified after it is created, if necessary.
When you specify the quantity of instances to be split, by default, any available capacity is split first, followed by any eligible running instances (the used capacity in your reservation). For example: if you split 4 instances from a Capacity Reservation with 5 used instances and 3 available instances, then the 3 available instances and 1 used instance will be split into a new reservation.
Prerequisites for splitting capacity
As a prerequisite, your Capacity Reservation must meet the following requirements:
-
The source reservation must be in the active state.
-
The source reservation must be owned by your Amazon Web Services account.
Note
When you split used capacity from your reservation by specifying a Quantity to split that's greater than the available
capacity, only the instances that were launched with their Capacity Reservation Specification as open
will be
split.
Considerations
The following considerations apply when splitting off capacity from one reservation to a new one:
-
The used capacity can only be split for Capacity Reservations with “open” instance eligibility that are not shared with any account.
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When you split the used capacity, the eligible instances are randomly selected. You cannot specify which running instances are split. If a sufficient number of eligible instances are not found to fulfill the split quantity, the split operation will fail.
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The maximum quantity of instances to split from an existing reservation is the size of the reservation minus one. For example, if your reservation’s total capacity is 5 instances, you can split a maximum of 4 instances into a new reservation.
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Future-dated Capacity Reservations – You can't split capacity for a future-dated Capacity Reservation during the commitment period.
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Resource groups – If the existing Capacity Reservation belongs to a resource group, the new Capacity Reservation will not be automatically added to the resource group. You can add the new Capacity Reservation to a resource group after it is created, if necessary.
-
Sharing – If the existing Capacity Reservation is shared with a consumer account, the new Capacity Reservation will not be automatically shared with the consumer account. You can share the new Capacity Reservation after it is created, if necessary.
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Cluster placement group – If the existing Capacity Reservation is part of a cluster placement group, the new Capacity Reservation will be created in the same cluster placement group.
Note
Splitting capacity from a Capacity Block isn't supported.
Control access for splitting Capacity Reservations using tags
You can use tags to control access to Amazon EC2 resources, including splitting capacity from an existing Capacity Reservation to create a new Capacity Reservation. For more information, see Controlling access to Amazon resources using tags in the IAM User Guide.
To control access for splitting a Capacity Reservation using tags, make sure that you specify both
resource and request tags in the policy statement because IAM policies are
evaluated against both the source Capacity Reservation and the newly created Capacity Reservation. The following
example policy includes the ec2:ResourceTag
condition key with the tag
Owner=ExampleDepartment1
for the source Capacity Reservation and the
ec2:RequestTag
condition key with the tag
stack=production
for the newly created Capacity Reservation.
{ "Statement": [ { "Sid": "AllowSourceCapacityReservation", "Effect": "Allow", "Action": "ec2:CreateCapacityReservationBySplitting", "Resource": "arn:aws:ec2:region:account:capacity-reservation/cr-1234567890abcdef0", "Condition": { "StringEquals": { "ec2:ResourceTag/Owner": "ExampleDepartment1" } } }, { "Sid": "AllowNewlyCreatedCapacityReservation", "Effect": "Allow", "Action": ["ec2:CreateCapacityReservationBySplitting", "ec2:CreateTags"], "Resource": "arn:aws:ec2:region:account:capacity-reservation/*", "Condition": { "StringEquals": { "ec2:RequestTag/stack": "production" } } } ] }
Split off capacity using the Amazon EC2 console or the Amazon CLI
To split off capacity from an existing Capacity Reservation and create a new Capacity Reservation, you can use the Amazon EC2 console or the Amazon CLI.