Beginning today, customers can implement instances of Windows Server 2003 (licensed to and purchased by them) in Amazon's cloud, enabling businesses to deploy sophisticated Internet applications without their own servers.

After a two-year beta cycle, Amazon's Elastic Computing Cloud (EC2) service this morning entered general availability. Now, for what's essentially a service, what does this mean besides removing the warning that some parts are still under construction? Today, Amazon implemented a service-level agreement for EC2 customers guaranteeing 99.95% availability during what it describes as a "service year."

EC2 services enable customers to deploy server-based applications in Amazon's cloud, which also encompasses its S3 storage service. Those services have been hosted under Linux and Unix environments, including Sun's Solaris, until earlier this month when the company unveiled a beta of Windows Server being hosted in Amazon's cloud.

"If the Annual Uptime Percentage for a customer drops below 99.95% for the Service Year, that customer is eligible to receive a Service Credit equal to 10% of their bill for the Eligible Credit Period," reads the SLA unveiled this morning. "To file a claim, a customer does not have to have wait 365 days from the day they started using the service or 365 days from their last successful claim. A customer can file a claim any time their Annual Uptime Percentage over the trailing 365 days drops below 99.95%."

Broken down, what that appears to say is that the EC2 customer has the right to evaluate whether his service at any time during the last year makes his 12-month total uptime fall below 99.95%. While the customer can file a claim during the first year, the SLA doesn't specify how it accounts for uptime estimates during the months he wasn't yet a customer. If recent usage levels are averaged out over the entire year, that could actually benefit the customer more than it does Amazon.

While EC2 has emerged from beta today, its Windows Server provisions remain in testing. However, today Windows Server 2003 instances are officially available, under a beta hosting service, for EC2. Running instances of WS2K3 are now purchasable on a per-hour basis, with prices starting at 12.5 cents per hour for small instances that typically use minimal bandwidth, ranging up to $3.20 per hour for a high-capacity CPU instance with SQL Server Standard edition and authentication services for more than five accounts.

Amazon will be providing basic EC2 instance management functions available to customers by means of a Firefox plug-in called ElasticFox (PDF available here). In future months, however, the company says it will be offering a more full-featured management console that enables real-time monitoring, and automatic features such as load balancing and scaling of cloud resources.

In a blog post this morning, Amazon Web Services developer Jeff Barr said, "I think it is important to note that load balancing, automatic scaling, and cloud monitoring will each be true web services, with complete APIs for provisioning, control, and status checking. We'll be working with a number of management tool vendors and developers to make sure that their products will support these new services on a timely basis."