Network interface getting not deleted

Best thing you can do is see what it is attached to.

On the ec2 console, in the left menu go to "Network & Security" "Network Interfaces" and look up the interface in question.

You can scroll a bit to the right to see the Description.

This will give you an indication by what it was/is used.

If it says it was for a Lambda you might have to wait up to 40 minutes.

If it is another resources still active in your account: well you found the reason it can't be deleted.

Merry Xmas. Jacco

When tracking down such issues in the past I have leveraged below.

• If you have AWS Config enabled you could search for the ENI resource to determine what is associated with the ENI.
• AWS Support Tools contains a simple bash script (findEniAssociations) that when given an ENI identifier and an AWS region will find if there are any Lambda functions currently using the specified ENI.