I'm trying to set up my own autoscaling system on AWS and I've set up alarms for any instance spawned with a specific AMI ID.
When I check the the metrics which are only monitoring one server, they get information just fine. The "aggregated" stats however always fail.
Is this a problem with AWS or does this not do what I think it does. I'll also point out these are all default metrics, not added through the CLI API.
Have you enabled detailed monitoring for your instances? AWS supports aggregated metrics only for instances with detailed monitoring enabled:
For the instances where you've enabled detailed monitoring, you can also get aggregated data across groups of similar instances.
See: http://docs.aws.amazon.com/AmazonCloudWatch/latest/DeveloperGuide/US_GetStatistics.html.