Remove Network interfaces created by AWS Lambda while undeploying stack

net_interfaces_cleanup.py

import boto3
from botocore.exceptions import ClientError
from time import sleep

# Fix this wherever your custom resource handler code is
from common import cfn_custom_resources as csr
import sys

MAX_RETRIES = 3
client = boto3.client('ec2')


def handler(event, context):

    vpc_id = event['ResourceProperties']['VPCID']

    if not csr.__is_valid_event(event, context):
        csr.send(event, context, FAILED, validate_response_data(result))
        return
    elif event['RequestType'] == 'Create' or event['RequestType'] == 'Update':
        result = {'result': 'Don\'t trigger the rest of the code'}
        csr.send(event, context, csr.SUCCESS, csr.validate_response_data(result))
        return
    try:
        # Get all network intefaces for given vpc which are attached to a lambda function
        interfaces = client.describe_network_interfaces(
            Filters=[
                {
                    'Name': 'description',
                    'Values': ['AWS Lambda VPC ENI*']
                },
                {
                    'Name': 'vpc-id',
                    'Values': [vpc_id]
                },
            ],
        )

        failed_detach = list()
        failed_delete = list()

        # Detach the above found network interfaces
        for interface in interfaces['NetworkInterfaces']:
            detach_interface(failed_detach, interface)

        # Try detach a second time and delete each simultaneously
        for interface in interfaces['NetworkInterfaces']:
            detach_and_delete_interface(failed_detach, failed_delete, interface)

        if not failed_detach or not failed_delete:
            result = {'result': 'Network interfaces detached and deleted successfully'}
            csr.send(event, context, csr.SUCCESS, csr.validate_response_data(result))
        else:
            result = {'result': 'Network interfaces couldn\'t be deleted completely'}
            csr.send(event, context, csr.FAILED, csr.validate_response_data(result))
            # print(response)
    except Exception:
        print("Unexpected error:", sys.exc_info())
        result = {'result': 'Some error with the process of detaching and deleting the network interfaces'}
        csr.send(event, context, csr.FAILED, csr.validate_response_data(result))


def detach_interface(failed_detach, interface):
    try:

        if interface['Status'] == 'in-use':
            detach_response = client.detach_network_interface(
                AttachmentId=interface['Attachment']['AttachmentId'],
                Force=True
            )

            # Sleep for 1 sec after every detachment
            sleep(1)

            print(f"Detach response for {interface['NetworkInterfaceId']}- {detach_response}")

            if 'HTTPStatusCode' not in detach_response['ResponseMetadata'] or \
                    detach_response['ResponseMetadata']['HTTPStatusCode'] != 200:
                failed_detach.append(detach_response)
    except ClientError as e:
        print(f"Exception details - {sys.exc_info()}")


def detach_and_delete_interface(failed_detach, failed_delete, interface, retries=0):

    detach_interface(failed_detach, interface)

    sleep(retries + 1)

    try:
        delete_response = client.delete_network_interface(
            NetworkInterfaceId=interface['NetworkInterfaceId'])

        print(f"Delete response for {interface['NetworkInterfaceId']}- {delete_response}")
        if 'HTTPStatusCode' not in delete_response['ResponseMetadata'] or \
                delete_response['ResponseMetadata']['HTTPStatusCode'] != 200:
            failed_delete.append(delete_response)
    except ClientError as e:
        print(f"Exception while deleting - {str(e)}")
        print()
        if retries <= MAX_RETRIES:
            if e.response['Error']['Code'] == 'InvalidNetworkInterface.InUse' or \
                    e.response['Error']['Code'] == 'InvalidParameterValue':
                retries = retries + 1
                print(f"Retry {retries} : Interface in use, deletion failed, retrying to detach and delete")
                detach_and_delete_interface(failed_detach, failed_delete, interface, retries)
            else:
                raise RuntimeError("Code not found in error")
        else:
            raise RuntimeError("Max Number of retries exhausted to remove the interface")