Connecting SQLBench to an AWS RDS for SQL Server instance is similar to connecting to an installed SQL Server instance, except that an AWS CloudWatch API Key is also required.
The AWS CloudWatch API Key allows SQLBench to collect "host" telemetry such as CPU utilization, Disk space, Available Memory etc.
It also allows the SQLBench Agent to enumerate AWS RDS instances available within the subscription, providing a convenient list of AWS RDS DB-Identifiers to choose from when adding an AWS RDS SQL Server instance.