query all EC2 instances for OS

The best way is to use AWS System Manager by enabling SSM agent on the EC2 instances.

https://repost.aws/knowledge-center/ec2-linux-find-os-platform-or-version https://docs.aws.amazon.com/systems-manager/latest/userguide/sysman-install-ssm-win.html

Here is an AWS CLI command to get the platform:

aws ec2 describe-instances \
    --query Reservations[*].Instances[*].[InstanceId,ImageId,PlatformDetails] \
    --output table

You can get further details about the platform:

aws ec2 describe-images \
    --image-ids ami-0d2f97c8735a48a15 \
    --query Images[*].[ImageId,Name,Description] \
    --output table