Most ArcGIS functionality is available on Amazon Web Services; however, this topic lists some features and configurations that are not supported.
Server clusters are not supported
ArcGIS Server clusters are not supported on Amazon Web Services. ArcGIS Server sites that you create in Amazon EC2 use the default cluster for all ArcGIS Server sites. Do not attempt to create additional clusters.
Amazon-imposed limitations
Amazon enforces some limitations on resources you can create, such as the size of EBS volumes, the number of EBS volumes you can attach to an instance, the number of instances you can run at once, and the number of Elastic IPs you can allocate in one region. Exceptions to the limitations are sometimes available upon request to Amazon.
For the most up-to-date and official information about Amazon limitations, see the AWS Documentation.