How do Amazon EC2 Reserved Instances work?

Last updated: 2019-06-28

I plan to use a particular instance configuration for steady-state workflows over a long period of time. Should I purchase a matching Reserved Instance?

Resolution

Amazon Elastic Compute Cloud (Amazon EC2) Reserved Instances (RIs) can provide two benefits over On-Demand EC2 instances:

  • A capacity reservation for that instance type.
  • A pricing discount that can help you save money.

These two benefits are provided to various levels depending on which Reserved Instance you choose. For example, Standard RIs provide the largest discount for a specific instance type over a long-term contract. Convertible RIs provide a smaller discount, but let you change the instance type during the contract.

Consider the following when deciding if Reserved Instances are right for you:

  • Reserved Instances have long contract terms (usually, one or three years). This means that you should only purchase reservations for an instance specification that you’ll use over the long term.
  • Most Reserved Instances are billed as a lump sum each month for each hour in that month. You're billed for this amount whether you ran an instance that matched your reservation or not. Reserved Instances provide the maximum discount for instance types that you use often and for long periods of time.
  • Reserved Instances can't be canceled, but some Reserved Instances can be modified, subject to certain restrictions. For information about the available types of modifications, see Modifying Your EC2 Reserved Instances.
  • If you decide you don't need an EC2 RI after you purchase it and you have access to a US bank account, you can sell the RI on the EC2 Reserved Instance Marketplace. For more details, see Amazon EC2 Reserved Instance Marketplace.
  • If your account is in an organization's consolidated billing family, additional considerations might apply. For more information, see How is the pricing benefit of a Reserved Instance applied across an organization's consolidated bill?

For more detailed information about and pricing for EC2 Reserved Instances, see Amazon EC2 Reserved Instances.

If you want to save money over the On-Demand price for a particular EC2 instance and you need to use that instance type only on a short-term basis, consider placing a bid for a Spot instance instead.


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