CloudFormation - Attached VPC Lambda stuck in DELETE_IN_PROGRESS - can't delete ENI

Question

I have a Lambda attached to a VPC in a CF stack and when I try to delete the stack the lambda will get stuck in DELETE_IN_PROGRESS for hours. If I try to manually delete the ENI it won't let me, with an error message eni is use by another service.

If I run the AWS script to detect what is using the ENI, I get a response that the ENI is not being used by any service. I can confirm that the lambda was deleted by going to the Lambda UI.

The only solution is to wait for a couple of hours until the ENI is deleted. This is very bad for us as we create a CF stack for our e2e tests before a new release and we can't wait for hours until is deleted.

Any workaround for this problem? The lambda role is only deleted after the Lambda is deleted.

Answer 1

I am facing the same problem with yours during my deployment with CloudFormation as well. And the provided helper script was not helpful in my case as well.

I believe that there is no way that we can disturb AWS managed ENIs which are created for your Lambda function. Maybe, I think they manage the deletion process over some signals sending to SQS queues or RabbitMQ.

Here is how I manage this:

• Firstly, I manage this by manually removing any VPC configuration from my Lambda functions.
• Then, I move forward with CloudFormation deletion or replacement.

This can solve waiting issues but will need to write some bash script to remove VPC configuration from those functions.