As in, most global services run primarily within us-east-1, and have only subsystems running in each region. For example, it's likely that the actual master da

As in, most global services run primarily within us-east-1, and have only subsystems running in each region. For example, it's likely that the actual master data stores for IAM are solely within us-east-1, but the key data is cached and services run in each region. Similarly, Cloudfront is theoretically a global service, but only ACM certificates set up within us-east-1 can be used with Cloudfront.