I noticed a bunch of these errors for Fleet distros. For instance, debian11-small has been getting this response some:
We currently do not have sufficient m5.xlarge capacity in the Availability Zone you requested (us-east-1a). Our system will be working on provisioning additional capacity. You can currently get m5.xlarge capacity by not specifying an Availability Zone in your request or choosing us-east-1b, us-east-1c, us-east-1d, us-east-1f.
I think the reason could be that we're only specifying a single subnet override in the CreateFleet request. Why is that? Is AWS telling us that it's the only AZ that supports the instance type?
This Splunk search shows the distros it's happening for.