You can now automatically launch Amazon EC2 Spot instances that have the lowest price per unit of capacity using the RequestSpotFleet API. You can define and set target capacity in any unit including instances, vCPUs, memory, storage, or network throughput. Since applications typically perform differently on different instance types, you can specify how much each instance type is worth, which automatically adjusts your bid price for each instance type. This enables you to bid on multiple instance types in a single request and provision cost-effective capacity available on any instance type.

Source: Amazon Web Services News