Can not remove or detach network interface

Question

I used k8s, eks, cloudformation stacks etc.

Now I can't delete the remaining network interface EVEN under the root account. I read that I have to search for related resources, such as the VPC, routing tables etc., and try to delete them first. I tried. Most of them couldn't be deleted because they were complaining that the network interface exists haha :) I also try to detach it, but always got errors. I have no elastic IP attached. I spent like 3 hours trying to remove this network interface and its related resources, nothing helped so far. I also tried to use the aws cli but the same results. I'm just getting an error: Failed to detach the network interface. API error: "You do not have permission to access the specified resource." I also tried to use --force with cli, didn't help. I can't delete, and can't detach the interface no matter what I do.

What should I even do? To me it seems really weird that I can't do anything even from my root user.

Answer

Hello.

I think you need to delete the resource that is using the network interface.  
For example, typical resources include ALB, Lambda connected to VPC, and EC2.  
First you need to find the resource that uses ENI.  
If you look at the ENI description column, there may be hints written there.

I think it will be easier to see if you run the following command with CloudShell etc.  
```
SUBNETID=subnet-yyyyyyyyyy

aws ec2 describe-network-interfaces\
 --filters Name=subnet-id,Values="$SUBNETID"\
 --query 'NetworkInterfaces[].{
     PrivateIpAddress:PrivateIpAddress,
     PublicIp:Association.PublicIp
     Name:TagSet[?Key==`Name`]|[0].Value,
     Description:Description,
     InstanceId:Attachment.InstanceId,
     NetworkInterfaceId:NetworkInterfaceId,
     Status:Status
 }'\
  --output json\
  | jq -r '
    .[] | [.PrivateIpAddress, .PublicIp, .Description, .Name,  .InstanceId, .NetworkInterfaceId, .Status] | @csv'\
  | sort -V -t "," -k 1
```

Can not remove or detach network interface

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