Question: How do I fix the circular dependency between an AWS Lambda permission and target group resources in AWS CloudFormation?

I want to fix the circular dependency between an AWS Lambda permission (AWS::Lambda::Permission) and target group resources (AWS::ElasticLoadBalancingV2::TargetGroup) in AWS CloudFormation.

Short descriptionYou get a circular dependency if you provide AWS::Lambda::Permission to AWS::ElasticLoadBalancingV2::TargetGroup instead of LoadBalancer to restrict access to your Lambda function. This is because the Lambda permission must exist before you associate the Lambda function to the target group that you want to create. When you create the Lambda permission, you must associate the permission with an AWS Principal and SourceARN (in this case, a target group). That's why the target group must exist before creating the Lambda permission. To fix this circular dependency, you can use a Lambda-backed custom resource.Resolution1.    Create a file named index.py that includes the following:Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.Permission is hereby granted, free of charge, to any person obtaining a copy of thissoftware and associated documentation files (the "Software"), to deal in the Softwarewithout restriction, including without limitation the rights to use, copy, modify,merge, publish, distribute, sublicense, and/or sell copies of the Software, and topermit persons to whom the Software is furnished to do so.THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR APARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHTHOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTIONOF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THESOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.def handler(event, context):     return {      "statusCode": 200,      "statusDescription": "HTTP OK",      "isBase64Encoded": False,      "headers": {         "Content-Type": "text/html"      },      "body": "<h1>Hello from Lambda!</h1>"    }Note: The AWS Lambda function in index.py displays an HTML page with the message "Hello from Lambda!" when the function is invoked.2.    Add the index.py file to an archive file named website.zip.3.    To create a .zip file of index.py, run the following command:$zip website.zip index.py4.    Create a file called cfnresponse.py based on the AWS CloudFormation template on AWS GitHub.5.    Create a filled called custom.py based on the following:Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.Permission is hereby granted, free of charge, to any person obtaining a copy of thissoftware and associated documentation files (the "Software"), to deal in the Softwarewithout restriction, including without limitation the rights to use, copy, modify,merge, publish, distribute, sublicense, and/or sell copies of the Software, and topermit persons to whom the Software is furnished to do so.THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR APARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHTHOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTIONOF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THESOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.import loggingimport boto3, json, botocoreimport cfnresponse#Define logging properties for 'logging'log = logging.getLogger()log.setLevel(logging.INFO)#Main Lambda function to be executeddef lambda_handler(event, context):    try:        if event['RequestType'] == "Create" or event['RequestType'] == "Update":            # print the event type sent from cloudformation            log.info ("'" + str(event['RequestType']) + "' event was sent from CFN")            # Imput Parameters            TargetGroupARN = event['ResourceProperties']['TargetGroupARN']            LambdaFunctionARN = event['ResourceProperties']['LambdaFunctionARN']            log.info("TargetGroup ARN value is:" + TargetGroupARN)            log.info("Lambda Function ARN value is:" + LambdaFunctionARN)            responseData = {}            # ELBV2 initilize            client = boto3.client('elbv2')            # Initilize Vars            response = ''            error_msg = ''            # Make the 1st API call to get the Lambda policy and extract SID of the initial permissions that were created by the CFN template.            try:                response = client.register_targets(                    TargetGroupArn=TargetGroupARN,                    Targets=[                        {                            'Id': LambdaFunctionARN                        },                    ]                )            except botocore.exceptions.ClientError as e:                error_msg = str(e)            if error_msg:                log.info("Error Occured:" + error_msg)                response_msg = error_msg                # TODO: SIGNAL BACK TO CLOUDFORMATION                log.info("Trying to signal FAILURE back to cloudformation.")                responseData = {"Message" : response_msg, "Function" : context.log_stream_name}                cfnresponse.send(event, context, cfnresponse.FAILED, responseData)            else:                response_msg = "Successfully Added Lambda(" +  LambdaFunctionARN + ") as Target"                log.info(response_msg)                # TODO: SIGNAL BACK TO CLOUDFORMATION                log.info("Trying to signal SUCCESS back to cloudformation.")                responseData = {"Message" : response_msg, "Function" : context.log_stream_name}                cfnresponse.send(event, context, cfnresponse.SUCCESS, responseData)                        # log the end of the create event            log.info ("End of '" + str(event['RequestType']) + "' Event")        elif "Delete" in str(event['RequestType']):            # print the event type sent from cloudformation            log.info ("'Delete' event was sent from CFN")                        # TODO: DELETE THINGS            log.info("TODO: DELETE THINGS")                        # TODO: SIGNAL BACK TO CLOUDFORMATION            log.info("Trying to signal SUCCESS back to cloudformation.")            responseData = {"Function" : context.log_stream_name}            cfnresponse.send(event, context, cfnresponse.SUCCESS, responseData)                        # log the end of the Delete event            log.info ("End of 'Delete' Event")        else:            log.info ("RequestType sent from cloudformation is invalid.")            log.info ("Was expecting 'Create', 'Update' or 'Delete' RequestType(s).")            log.info ("The detected RequestType is : '" + str(event['RequestType']) + "'")                        #TODO: SIGNAL BACK TO CLOUDFORMATION            log.info("Trying to signal FAILURE back to cloudformation due to invalid request type.")            responseData={"Function" : context.log_stream_name}            cfnresponse.send(event, context, cfnresponse.FAILED, responseData)                            except Exception as e:        log.info ("Function failed due to the following error:")        print (e)                #TODO: SIGNAL BACK TO CLOUDFORMATION        log.info("Trying to signal FAILURE back to cloudformation due to the error.")        responseData={"Function" : context.log_stream_name}        cfnresponse.send(event, context, cfnresponse.FAILED, responseData)Note: The Lambda function in custom.py performs the RegisterTargets API call and signals AWS CloudFormation on completion of that API call.6.    Add the cfnresponse.py and custom.py files to an archive file named custom.zip. For example:zip custom.zip cfnresponse.py custom.pyNote: The custom.py file uses the Boto3 API call RegisterTargets. This API call registers the specified targets with the specified target group. For more information, see the register_targets Python snippet from the Boto3 website. The cfnresponse.py file contains a function that pushes logs and notifications to Amazon CloudWatch and AWS CloudFormation.7.    Create an AWS CloudFormation template using the following YAML template:Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.Permission is hereby granted, free of charge, to any person obtaining a copy of thissoftware and associated documentation files (the "Software"), to deal in the Softwarewithout restriction, including without limitation the rights to use, copy, modify,merge, publish, distribute, sublicense, and/or sell copies of the Software, and topermit persons to whom the Software is furnished to do so.THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR APARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHTHOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTIONOF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THESOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.AWSTemplateFormatVersion: 2010-09-09Description: HelloWorld Lambda function template for Application Load Balancer Lambda as targetParameters:  # VPC in which the LoadBalancer and the LoadBalancer SecurityGroup will be created  VpcId:      Type: AWS::EC2::VPC::Id  # Subnets in which the LoadBalancer will be created.  Subnets:    Type: List<AWS::EC2::Subnet::Id>  # Name of the TargetGroup  TargetGroupName:     Type: String    Default: 'MyTargets'  # Name of the S3 bucket where custom.zip and website.zip are uploaded to   S3BucketName:    Type: String    Default: you-s3-bucket-nameResources:  LambdaExecutionRole:    Type: AWS::IAM::Role    Properties:      AssumeRolePolicyDocument:        Version: '2012-10-17'        Statement:        - Effect: Allow          Principal:            Service:            - lambda.amazonaws.com          Action:          - sts:AssumeRole      Path: "/"      Policies:      - PolicyName: root        PolicyDocument:          Version: '2012-10-17'          Statement:          - Effect: Allow            Action:            - '*'            Resource: '*'  # Lambda function which displays an HTML page with "Hello from Lambda!" message upon invocation  HelloWorldFunction1234:    Type: 'AWS::Lambda::Function'    Properties:      Code:        S3Bucket: !Ref S3BucketName        S3Key: website.zip      FunctionName: testLambda      MemorySize: 128      Handler: index.handler      Timeout: 30      Runtime: python3.7      Role: !GetAtt LambdaExecutionRole.Arn  LoadBalancer:    Type: AWS::ElasticLoadBalancingV2::LoadBalancer    Properties:      Scheme: internet-facing       Subnets: !Ref Subnets      SecurityGroups:      - !Ref LoadBalancerSecurityGroup  HttpListener:    Type: 'AWS::ElasticLoadBalancingV2::Listener'    Properties:      DefaultActions:      - TargetGroupArn: !Ref TargetGroup        Type: forward      LoadBalancerArn: !Ref LoadBalancer      Port: 80      Protocol: HTTP  LoadBalancerSecurityGroup:    Type: AWS::EC2::SecurityGroup    Properties:      GroupDescription: Allow http to client host      VpcId: !Ref VpcId      SecurityGroupIngress:      - IpProtocol: tcp        FromPort: 80        ToPort: 80        CidrIp: 0.0.0.0/0  HelloWorldFunctionInvokePermission:    Type: AWS::Lambda::Permission    Properties:      FunctionName: !GetAtt HelloWorldFunction1234.Arn      Action: 'lambda:InvokeFunction'      Principal: elasticloadbalancing.amazonaws.com      SourceArn: !Sub         - >-          arn:aws:elasticloadbalancing:${AWS::Region}:${AWS::AccountId}:${TGFullName}        - TGFullName: !GetAtt TargetGroup.TargetGroupFullName  TargetGroup:    Type: AWS::ElasticLoadBalancingV2::TargetGroup    Properties:      Name: !Ref TargetGroupName      TargetType: lambda  # Custom resource for Lambda function - "HelloWorldFunction1234"  HelloWorld:    DependsOn: [TargetGroup, HelloWorldFunctionInvokePermission]    Type: Custom::HelloWorld    Properties:      ServiceToken: !GetAtt TestFunction.Arn      # Input parameters for the Lambda function      LambdaFunctionARN: !GetAtt HelloWorldFunction1234.Arn      TargetGroupARN: !Sub         - >-          arn:aws:elasticloadbalancing:${AWS::Region}:${AWS::AccountId}:${TGFullName}        - TGFullName: !GetAtt TargetGroup.TargetGroupFullName  # Lambda function that performs RegisterTargets API call  TestFunction:    Type: AWS::Lambda::Function    Properties:      Code:        S3Bucket: !Ref S3BucketName        S3Key: custom.zip      Handler: custom.lambda_handler      Role: !GetAtt LambdaExecutionRole.Arn      Runtime: python3.7      Timeout: '5'Outputs:  Message:    Description: Message returned from Lambda    Value: !GetAtt       - HelloWorld      - Message8.    Pass in your values for the S3BucketName, Subnets, VpcId, and TargetGroupName parameters to the AWS CloudFormation stack that you created using the template in step 7.9.    Create the stack.10.    After all the API calls are completed, go to the Outputs section of the AWS CloudFormation console, and then look for the following message:Successfully Added Lambda(arn:aws:lambda:us-east-1:123456789:function:testLambda) as Target