Amazon EC2 provides multiple regions so you can launch Amazon EC2 instances in locations that meet your requirements. For example, you might want to launch instances in Europe to be closer to your European customers or to meet legal requirements.
Each Amazon EC2 region is designed to be completely isolated from the other Amazon EC2 regions. This achieves the greatest possible failure independence and stability, and it makes the locality of each EC2 resource unambiguous.
Example 742. Viewing the available regions
describe is used to find out which regions your account has access to.
describe will return an array containing information about which
regions are available. Each array will contain regionName and regionUrl.
<?php
$ec2_region = new Zend_Service_Amazon_Ec2_Region('aws_key','aws_secret_key');
$regions = $ec2_region->describe();
foreach($regions as $region) {
print $region['regionName'] . ' -- ' . $region['regionUrl'] . '<br />';
}