The AWS Doc states, "You can aggregate the metrics for AWS resources across multiple resources. Amazon CloudWatch can't aggregate data across Regions. Metrics are completely separate between Regions".
But then it follows by an example which states, "For example, you can aggregate statistics for your EC2 instances that have detailed monitoring enabled. Instances that use basic monitoring aren't included. Therefore, you must enable detailed monitoring (at an additional charge), which provides data in 1-minute periods."
As a reader of that document, I am left wondering if "ALL INSTANCES" mean
"All instances within that region" or
"All instance across region"
Appreciate your inputs. Thanks in advance!
This means all instances within region.
You can get metrics from different region onto the same graph for sure. To have them aggregated together using metric math check out this feature: https://aws.amazon.com/about-aws/whats-new/2019/11/amazon-cloudwatch-launches-cross-account-cross-region-dashboards/
From there:
You can also use CloudWatch metric math to aggregate and transform metrics from multiple accounts and Regions.