The easiest way to check whether or not an instance is using an EIP is to see if the public DNS name and (Public) IP address match your Elastic IP.
Also, on the Info tab, you can view specific User Data information.
Note: The "User Data" information does not list the current IP address of the instance; it lists the IP address that was originally used to launch the instance, so sometimes the listed IP will be a mismatch from what is listed above.
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