You want two Cloud Routers where one has an active BGP session and the other is standby. Which BGP attribute on your on-prem router enforces this active/standby behavior?

The Multi-exit Discriminator (MED) attribute is used to influence how traffic enters an autonomous system (AS) when there are multiple entry points. A lower MED value is preferred. By configuring a lower MED on the BGP session for the active Cloud Router and a higher MED on the standby Cloud Router, you can direct incoming traffic to the active router, establishing an active/standby setup. AS-Path is used for loop prevention and path selection based on path length. Community is a tag used for grouping routes and applying policies, not for active/standby. Local Preference influences outbound traffic from an AS, not inbound traffic.