Reserving EC2 Instances for Long-Term Use（ec2折扣）

详细查看：

Reserving Amazon EC2 Instances for Long-Term Use

Amazon EC2 now supports an additional pricing option. With Amazon EC2 Reserved Instances, you can make a low one-time payment for each instance to reserve and receive a significant discount on the hourly usage charge for that instance.

Amazon EC2 Reserved Instances are based on instance type and location (region and Availability Zone) for a specified period of time (e.g., 1 year or 3 years).

比如：你可以在us-east-1c区域购买类型为c1.medium的实例3年的运行服务，购买的数量为2个，需要的费用一共是2x1000美元，这样，当你在购买服务的3年内运行us-east-1c的2个c1.medium实例，每个实例每小时的运行费用为0.06美元，相对于原来的0.20美元有了不小的降幅。

On-Demand Instances

Reserved Instances

How do I control which instances are billed at the Reserved Instance rate?

The RunInstances command does not distinguish between On-Demand and Reserved Instances. When computing your bill, our system will automatically optimize which instances are charged at the lower Reserved Instance rate to ensure you always pay the lowest amount.

更多查看reserver instance的FAQ