How would I find out if Reserved Instance is being used?

Hi,

You can check whether your reserved instance is being used by going to the AWS Management console, click on Services, in the search bar type in “Billing” click on billing, this will take you to the Billing and Cost Management Dashboard. Once there on the left navigation pane click “Bills” under the Elastic Cloud Compute drop down list, select the region which your Reserved and On Demand instance’s are. You will then be able to see which instances are being used and the cost associated with that use [1].

Hope this helps!
/MrK

References
[1] https://aws.amazon.com/premiumsupport/knowledge-center/ec2-reserved-instances-being-used/