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) and are only available for Linux or UNIX instances. 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. describeInstances() will return information about a reserved instance or instances that you purchased. describeInstances() returns a multi-demential array that contains reservedInstancesId, instanceType, availabilityZone, duration, fixedPrice, usagePrice, productDescription, instanceCount and state. describeInstances('instanceId'); ]]> describeOfferings() Describes Reserved Instance offerings that are available for purchase. With Amazon EC2 Reserved Instances, you purchase the right to launch Amazon EC2 instances for a period of time (without getting insufficient capacity errors) and pay a lower usage rate for the actual time used. describeOfferings() returns a multi-demential array that contains reservedInstancesId, instanceType, availabilityZone, duration, fixedPrice, usagePrice and productDescription. describeOfferings(); ]]> purchaseOffering() Purchases a Reserved Instance for use with your account. With Amazon EC2 Reserved Instances, you purchase the right to launch Amazon EC2 instances for a period of time (without getting insufficient capacity errors) and pay a lower usage rate for the actual time used. purchaseOffering() returns the reservedInstanceId. purchaseOffering('offeringId', 'instanceCount'); ]]>