Most ArcGIS functionality is available on Amazon Web Services (AWS); however, this topic lists some features and configurations that are not supported.
Limitations related to the use of the Elastic Load Balancer (ELB) and the Web ADF
The use of Elastic Load Balancers (ELBs) for scaling on Amazon Web Services constrains a few specific features of ArcGIS Server. ELBs are configured by default when you launch an ArcGIS Server site or deploy ArcGIS Enterprise using ArcGIS Enterprise Cloud Builder Command Line Interface for Amazon Web Services or the Amazon CloudFormation templates Esri provides. The ELBs broker incoming requests across any of your instances participating in the site; that is, there is no guarantee that requests from a particular client (web browser user session, desktop client, or mobile application) will be handled by a particular EC2 instance. This limits the use of stateful web applications.
ArcGIS Server Web Application Developer Framework (ADF) applications rely on user session information that is stored at the web tier (in Internet Information Services). For the Web ADF application to work, incoming requests from a user session (web browser) have to hit the EC2 instance in which the session information is being stored. As described previously, an ELB does not guarantee that.
Advanced users can accommodate this limitation by using sticky sessions. Amazon provides several scripts to configure these in the ELB; however, Esri has not certified these configurations in Amazon EC2.
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 AWS limitations, see the AWS documentation.