Reserved Instances are applied to instances that meet the type/location criteria during the specified period. In this example, a user is running the following instances:
(4) m1.small instances in Availability Zone us-east-1a
(4) c1.medium instances in Availability Zone us-east-1b
(2) c1.xlarge instances in Availability Zone us-east-1b
The user then purchases the following Reserved Instances.
(2) m1.small instances in Availability Zone us-east-1a
(2) c1.medium instances in Availability Zone us-east-1a
(2) m1.xlarge instances in Availability Zone us-east-1a
Amazon EC2 applies the two m1.small Reserved Instances to two of the instances in Availability Zone us-east-1a. Amazon EC2 doesn't apply the two c1.medium Reserved Instances because the c1.medium instances are in a different Availability Zone and does not apply the m1.xlarge Reserved Instances because there are no running m1.xlarge instances.