The Amazon Elastic Compute Cloud (Amazon EC2) is a Web-based service that allows business subscribers to run application programs in the Amazon.com computing environment. The EC2 can serve as a practically unlimited set of virtual machines.
To use the EC2, a subscriber creates an Amazon Machine Image (AMI) containing the operating system, application programs and configuration settings. Then the AMI is uploaded to the Amazon Simple Storage Service (Amazon S3) and registered with Amazon EC2, creating a so-called AMI identifier (AMI ID). Once this has been done, the subscriber can requisition virtual machines on an as-needed basis. Capacity can be increased or decreased in real time from as few as one to more than 1000 virtual machines simultaneously. Billing takes place according to the computing and network resources consumed.