Tim Anderson

Sun has been talking up grid computing for years, but it is the e-commerce giant Amazon that is bringing on-demand server capacity to the mass market. Its Elastic Compute Cloud, or EC2, lets you run up virtual server instances programmatically, via a web service API.

With EC2, each Linux server is the equivalent of a 1.7GHz Xeon with 160GB hard drive, and you pay $0.10 per hour while it is running. The value is fair even if the system is running continuously, but it is with intermittent use that the savings really kick in. You can configure your own server images so that instances are ready to run your applications as soon as they come online.

The EC2 service is flexible, and three appropriate uses immediately come to mind. The first is for scaling applications dynamically, bringing up new server instances as needed. The second is for parallel computing, using a number of EC2 servers to perform intensive computational tasks. The third is for test and development. Virtual hosting is ideal for this, letting you experiment with different configurations in a live internet setting.

The Elastic Compute Cloud has just gone into beta, and there are a few snags with the service. The most obvious is that when a server is shut down or crashes, that instance is gone forever. But even real servers fail, so arguably EC2 just highlights the fact that you should not entrust just one machine with important data. Amazon also offers its S3 Simple Storage Service, which lets you read and write data to a more resilient location using another web service API.

S3 is also used to store server images, and there is a natural synergy between EC2 and S3. Perhaps the biggest issue is the lack of a service-level agreement (SLA) for either EC2 or S3, though the S3 service has proved reliable to date.

Why is Amazon getting into virtual hosting? "We don't view this as virtual hosting," said Peter De Santis, Director of Amazon EC2, describing it as a " core building block" for developers, adding that "we are building Amazon EC2 to scale with demand".

Why bother with a web service API, as opposed to a control panel? "The most obvious benefit is that developers can programmatically manage their computing needs," De Santis said. How does EC2 compare with other grid computing initiatives? "It is unique because it gives developers complete control of their instances," he argued.

My take is that there is something remarkable about the ability to go from zero to 10 or more servers in a matter of minutes. The other notable feature of EC2, as with Amazon's other web services, is the low price of entry. Highly scalable applications are now within anyone's reach.

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