Reserved Instances provide you with a significant discount compared to On-Demand Instance pricing. Reserved Instances are not physical instances, but rather a billing discount applied to the use of On-Demand Instances in your account. These On-Demand Instances must match certain attributes in order to benefit from the billing discount.
When you purchase Reserved Instances in a specific Availability Zone, they provide a capacity reservation. You can choose to forego this capacity reservation, by purchasing Reserved Instances in a specific region (regional Reserved Instances). These regional Reserved Instances provide Availability Zone and instance size flexibility. Availability Zone flexibility provides the Reserved Instance discount to instance usage in any Availability Zone in a region. Instance size flexibility provides the Reserved Instance discount to instance usage regardless of size, within that instance family. For more information, see Applying Reserved Instances.
When you purchase a Reserved Instance, choose a payment option, term, and an offering class that suits your needs. Generally speaking, you can save more money choosing Reserved Instances with a higher upfront payment. There are three payment options (No Upfront, Partial Upfront, All Upfront), two term lengths (one-year or three-years), and two offering classes (Convertible and Standard).
No Upfront and Partial Upfront Reserved Instances are billed for usage on an hourly basis, regardless of whether they are being used. All Upfront Reserved Instances have no additional hourly charges.
Convertible Reserved Instances can be exchanged during the term for Convertible Reserved Instances with new attributes including instance type. Standard Reserved Instances can be modified during the term, but the instance type is fixed throughout the term.
You can find Reserved Instances offered by third-party sellers at shorter term lengths and lower prices as well. For more information, see Reserved Instance Marketplace.
Reserved Instances do not renew automatically; when they expire, you can continue using the EC2 instance without interruption, but you are charged On-Demand rates. New Reserved Instances can have the same parameters as the expired ones, or you can purchase Reserved Instances with different parameters.
You can use Auto Scaling or other AWS services to launch the On-Demand Instances that use your Reserved Instance benefits. For information about launching On-Demand Instances, see Launch Your Instance. For information about launching instances using Auto Scaling, see the Auto Scaling User Guide.
For more information about product pricing information, see the following:
For information about the Reserved Instance pricing tiers, see Understanding Reserved Instance Discount Pricing Tiers.