The data layer is DynamoDB with Global Tables providing replication between regions, so we can write to any region. It's not easy to get this right, but our use case is narrow enough and rate of change low enought (intentionally) that it works well. That said, it still isn't clear that replication to us-east-1 would be perfect so we did "diff" tables just to be sure (it has been for us).

There is some S3 replication as well in the CI/CD pipeline, but that doesn't impact our customers directly. If we'd seen errors there it would mean manually taking Virginia out of the pipeline so we could deploy everyehere else.