You may be able to save on future EC2 expenses by selling an unused Reserved Instance for less than its true value or even $0.01, provided it is in the “Heavy Utilization” class.
In the description of the Heavy Utilization Reserved Instance, is this statement:
you pay […] a significantly lower hourly usage fee, and you’re charged that lower hourly rate for every hour in the Reserved Instance term you purchase [emphasis added]
What may not be clear to the casual reader is the fact that when you purchase a Heavy Utilization Reserved Instance, you commit not only to paying the one-time up front cost, but you are also committing to paying the hourly charge for every hour of every month, even if you are not running a matching instance!
The Light Utilization and Medium Utilization descriptions state:
Light [and Medium] Utilization RIs allow you to turn off your instance at any point and not pay the hourly fee.
This statement is conspicuously missing from the Heavy Utilization description.
If you buy a 12 month Heavy Utilization Reserved Instance and you only run the matching instance for 5 months and then terminate it, you still pay hourly instance charges each of the next 7 months as if you were still running the instance.
How to Save
Amazon just opened the Reserved Instance Marketplace, which lets you sell the remaining months on a Reserved Instance that you no longer need. After you list a Reserved Instance, it will be shown to EC2 customers when they look to purchase a Reserved Instance, right along with Amazon’s normal offerings.
When you list a Reserved Instance for sale, Amazon suggests a price that matches what the Reserved Instance would be worth to somebody purchasing the remaining months.
Though you would surely prefer to get that value (minus Amazon’s 12% commission) for the Reserved Instance, you might consider listing it for substantially less, especially while the Marketplace has fewer buyers and listings take longer to sell.
For every month that your Heavy Utilization Reserved Instance does not sell on the Reserved Instance Marketplace, you end up paying Amazon the hourly instance charges for the month, even if you are not running a matching instance.
If you give away the Heavy Utilization Reserved Instance by listing it for $0.01 it should sell fairly quickly in a rational marketplace, and you will not have to pay the hourly instance charges for the remaining months.
Thus, giving away a Heavy Utilization Reserved Instance could save you a bundle if you no longer need it.
If there is a non-zero chance you may want to run a matching instance before the end of the term, then the Reserved Instance has some positive value to you and you might consider holding on to it or listing it for a higher price, even though you need to pay when the instance is not running.
Figuring out the optimal listing price between $0.01 and a price near Amazon’s suggested listing price is left as an exercise for the reader.