http://aws.amazon.com/ec2/reserved-instances
http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/concepts-on-demand-reserved-instances.html
There are three Reserved Instance types (Light, Medium, and Heavy Utilization) that enable you to balance the amount you pay upfront with your effective hourly price. If your needs change, you can request to move your Reserved Instance to another Availability Zone within the same region, change its Network Platform, or, for Linux/UNIX and Windows RIs, modify the instance type of your reservation to another type in the same instance family at no additional cost. You can also sell your Reserved Instances to other customers via the Reserved Instance Marketplace if you have a US bank account.
Reserved Instances can be purchased directly from AWS for 1 or 3 year terms. Using the Reserved Instance Marketplace, you have the flexibility to purchase Reserved Instances from AWS Reserved Instance Marketplace Sellers for terms ranging between 1 month to 36 months (depending on available selection). In either case, the one-time fee per instance is non-refundable. If your needs change, you can also request to move your Reserved Instance to another Availability Zone within the same region, change its Network Platform, or, for Linux/UNIX and Windows RIs, modify the instance type of your reservation to another type in the same instance family at no additional cost.
Light and Medium Utilization Reserved Instances also are billed by the instance-hour for the time that instances are in a running state; if you do not run the instance in an hour, there is zero usage charge. Partial instance-hours consumed are billed as full hours. Heavy Utilization Reserved Instances are billed for every hour during the entire Reserved Instance term (which means you’re charged the hourly fee regardless of whether any usage has occurred during an hour).
If Microsoft or Red Hat chooses to increase the license fees that it charges for Windows or Red Hat Enterprise Linux, we may correspondingly increase the per-hour usage rate for previously purchased Reserved Instances with Windows or Red Hat Enterprise Linux. The initial one-time payment for a Reserved Instance will be unaffected in this situation. Any such changes for Windows would be made between Dec 1 – Jan 31, and with at least 30 days’ notice. Any such changes for Red Hat Enterprise Linux would be made at least 30 days’ notice. If the per-hour usage rate does increase, you may continue to use your Reserved Instance with Windows or Red Hat Enterprise Linux with the new per-hour usage rate, convert your Reserved Instance with Windows or Red Hat Enterprise Linux to a Reserved Instance with Linux/UNIX, or request a pro rata refund of the upfront fee you paid for the Reserved Instance with Windows or Red Hat Enterprise Linux.
Reserved Instances are available for Linux/UNIX, Windows, Red Hat Enterprise Linux, and SUSE Linux Enterprise operating systems. You can also optionally reserve instances in Amazon VPC at the same prices as shown above.
Reserved Instance Volume Discounts:
When you have purchased a sufficient number of Reserved Instances in an AWS Region, you will automatically receive discounts on your upfront fees and usage fees for future purchases of Reserved Instances in that AWS Region. Reserved Instance Tiers are determined based on the total list price (non-discounted price) of upfront fees for the active Reserved Instances you have per AWS Region. It is important to note that Reserved Instance Tiers do not apply to Reserved Instances purchased from the Reserved Instance Marketplace. A complete list of the Reserved Instance Tiers is shown below (see http://aws.amazon.com/ec2/#pricing)
For example, as soon as you have active Reserved Instances with total list price of upfront fees totaling more than $250,000 in a single AWS Region, you will automatically receive a 10% discount on both upfront and hourly fees for all future Reserved Instance purchases in that AWS Region, and those discounts will continue to apply to new Reserved Instances as long as you continue to qualify for the discount tier.
To illustrate, let's assume you currently have $200,000 worth of active Reserved Instances in us-east-1. You purchase 75 Reserved Instances at $1000 each. That's a total of $75,000. The first $50,000 of this purchase would be discounted at 0 percent. The remaining $25,000 of your purchase will be discounted by 10 percent, so you will only be charged $22,500 for it, and you will pay discounted hourly fees on those Reserved Instances.
To learn more about Reserved Instance Tiers, please visit the “Understanding Reserved Instance Tiers”
