Concepts for Amazon EC2 Capacity Reservations
The following key concepts apply to Capacity Reservations.
Topics
Start date and time
The start date and time defines when the Capacity Reservation becomes available for use. A Capacity Reservation can start immediately, or it can start at a future date.
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If you choose to start a Capacity Reservation immediately, the reserved capacity becomes available for use immediately after you create it, and billing starts as soon as the Capacity Reservation enters the active state. You do not need to enter into any term commitments. You can modify the Capacity Reservation as needed at any time to meet your needs, and you can cancel it at any time to release the capacity and to stop incurring charges.
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If you choose to start a Capacity Reservation at a future date, you specify a future date and time at which you will need the reserved capacity, and a commitment duration, which is the minimum duration for which you commit to keeping the requested Capacity Reservation in your account after it has been provisioned. At the specified future date, the Capacity Reservation becomes available for use and billing starts at that time, once the Capacity Reservation enters the active state. The commit duration starts as soon as the Capacity Reservation is provisioned in your account. During this time, you can't decrease the instance count below the committed instance count, choose an end date that is before the commitment duration, or cancel the Capacity Reservation. However, after the commitment duration lapses, you are free to modify the Capacity Reservation in any way, or cancel it to release the reserved capacity and to stop incurring charges.
End date and time
The end date and time defines when the Capacity Reservation ends and the reserved capacity is released from your account. You can configure a Capacity Reservation to end automatically at a specific date and time, or you can configure it to stay active indefinitely until you manually cancel it.
If you configure a Capacity Reservation to end automatically, the Capacity Reservation the Capacity Reservation
expires within an hour of the specified time. For example, if you specify
5/31/2019, 13:30:55, the Capacity Reservation is guaranteed to end between
13:30:55 and 14:30:55 on
5/31/2019.
After a reservation ends, the reserved capacity is released from your account and you can no longer target instances to the Capacity Reservation. Instances running in the reserved capacity continue to run uninterrupted. If instances targeting a Capacity Reservation are stopped, you can't restart them until you remove their Capacity Reservation targeting preference or configure them to target a different Capacity Reservation. For more information, see Modify the Capacity Reservation settings of your instance.
Commitment duration
The commitment duration applies to future-dated Capacity Reservations only.
The commitment duration is a minimum duration for which you commit to having the future-dated Capacity Reservation in the active state in your account after it has been provisioned. You can keep a future-dated Capacity Reservation for longer than the commitment duration, but not shorter. The following apply during the commitment duration:
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You can't cancel a Capacity Reservation during the commitment duration.
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You can't decrease the instance count below the committed instance count, but you can increase it.
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You can't configure a Capacity Reservation to automatically end at a date or time that is within the commitment duration. You can extend the end date and time during the commitment period.
Amazon EC2 uses the commitment duration that you specify to assess whether the request can be supported. For most requests, the recommended commitment duration is 14 days. While assessing a request, Amazon EC2 might determine that it can support a shorter commitment duration. In that case, Amazon EC2 will schedule the future-dated Capacity Reservation with the shorter commitment duration. This means that you are committed to keeping the Capacity Reservation in your account for a shorter period than you initially requested.
Future-dated Capacity Reservation assessment
When you request a future-dated Capacity Reservation, Amazon EC2 assesses the request to determine whether it can be supported based on capacity availability and the commitment duration you specify. The assessment is typically completed within 5 days. Amazon EC2 considers multiple factors when evaluating a request, including:
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Forecasted capacity supply
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The commitment duration
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How early you request the Capacity Reservation relative to your start date
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The size of your request
Requesting a future-dated Capacity Reservation early (more than 8 weeks before the start date), and increasing your minimum commitment duration will improve our ability to support your request. For most requests, the recommended commitment duration is 14 days.
The Capacity Reservation remains in the assessing state while the request is being
assessed.
If the request can be supported, the Capacity Reservation enters the scheduled state
and it is scheduled for delivery on the requested date and time. The total instance
count remains 0 during while the Capacity Reservation is in the scheduled state. A
scheduled Capacity Reservation will become active and available for use at the
requested date.
If a request can't be supported, the Capacity Reservation enters the unsupported
state. Unsupported Capacity Reservations are not delivered.
You can cancel a future-dated Capacity Reservation while it is in the assessing state.
Capacity Reservation attributes
When you create a Capacity Reservation, you must specify the following attributes:
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Availability Zone
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Instance type
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Platform (operating system type)
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Tenancy (
defaultordedicated)
Only instances that match these attributes can launch or run in the Capacity Reservation.
Instance matching criteria
Instance matching criteria, or instance eligibility, determines which instances are allowed to launch and run in the Capacity Reservation. A Capacity Reservation can have one of the following matching criteria:
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Open — The Capacity Reservation automatically matches all instances that have matching attributes (instance type, platform, and Availability Zone). New and existing instances that have matching attributes automatically run in the Capacity Reservation without any additional configuration.
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Targeted — The Capacity Reservation accepts only instances that have matching attributes (instance type, platform, and Availability Zone), and that explicitly target the Capacity Reservation. The instance must specifically target the Capacity Reservation to launch or run in its reserved capacity. This allows you to explicitly control which instances are allowed to run in the reserved capacity and helps you avoid unintentional reserved capacity usage.
When you request a future-dated Capacity Reservation, you can specify only targeted matching criteria. This ensures that the capacity delivered by the Capacity Reservation is incremental, or additional, to any running instances or reserved capacity that you have at the time of delivery. After the Capacity Reservation becomes active in your account, you can change the instance matching criteria to open if needed. However, keep in mind that any matching instances will automatically run in the Capacity Reservation, which could lead to unintentional capacity usage and prevent you from launching new instances for the full requested instance count.
