Using Capacity Reservation in placement groups with a Capacity Reservation group
Amazon EC2 provides different launch methods for you to use Capacity Reservations in a placement group with a Capacity Reservation group. You can choose one of the following methods to target a Capacity Reservation group based on your workload requirements:
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Specifying the ARN of the placement group and Capacity Reservation group – This will use any available Capacity Reservation with matching attributes and available capacity in the selected Capacity Reservation group. If the selected group does not have a Capacity Reservation with matching attributes and available capacity, the instances launch into On-Demand capacity.
Note
When you launch instances using this method, the instances are placed in the specified placement group.
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Specifying only a Capacity Reservation group – This will use all available capacity within the Capacity Reservation group by specifying only the Capacity Reservation group. While launching instances, capacity is used in the following order:
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Capacity Reservations not in any placement group.
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Capacity Reservation in any placement group within the Capacity Reservation group.
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If the group does not have a Capacity Reservation with matching attributes and available capacity, the instances run using On-Demand capacity and they are not placed in any placement group.
Note
When you launch instances by specifying only a Capacity Reservation group, the instances are launched into the Capacity Reservations that are created in the placement group, but the instances are not directly attached to the placement group.
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