Unable to delete network interfaces attached to VPC Endpoint

Maybe this post will help to find a ressource attached to the interface: https://aws.amazon.com/premiumsupport/knowledge-center/troubleshoot-dependency-error-delete-vpc/ and the CLI command describe-network-interfaces: https://docs.aws.amazon.com/cli/latest/reference/ec2/describe-network-interfaces.html

I ended up answering my own question. I had an Aurora Serverless DB in a VPC, which creates a VPC endpoint and related network interfaces which are considered "requester-managed". Once I deleted the database, the above resources disappeared.

Though it had been 2 years ago. This is the question where Google search of ENI “Network interface is in use by another service” will bring at the top. Let me add some more information I found useful. I had the similar issue as the question. I could not figure out what held my ENI. Use this CLI (https://docs.aws.amazon.com/cli/latest/reference/ec2/describe-network-interfaces.html) as rePost-User-5170769 pointed out. For example, if you search eni-123412341234 (I converted every unique values to 123412341234) in the below snippet of output of aws ec2 describe-network-interfaces, you see that Description: field has the hint.

            “Description”: “EFS mount target for fs-123412341234 (fsmt-123412341234)”,  <=== this is a sample hint you want
            “Groups”: [
                {
                    “GroupName”: “security-group-for-inbound-nfs-d-123412341234”,
                    “GroupId”: “sg-123412341234”
                }
            ],
            “InterfaceType”: “efs”,
            “Ipv6Addresses”: [],
            “MacAddress”: “<snip>“,
            “NetworkInterfaceId”: “eni-123412341234”, <=== this is your search point

I deleted the unused EFS resources and then the VPC deletion was successful.