Come posso correggere la dipendenza circolare tra un'autorizzazione AWS Lambda e le risorse del gruppo target in AWS CloudFormation?

Breve descrizione

Ottieni una dipendenza circolare se fornisci AWS::Lambda::Permission ad AWS::ElasticLoadBalancingV2::TargetGroup invece di LoadBalancer per limitare l'accesso alla tua funzione Lambda. Questo perché l'autorizzazione Lambda deve esistere prima di associare la funzione Lambda al gruppo target che si vuole creare. Quando crei l'autorizzazione Lambda, devi associarla a un Principal e SourceARN AWS (in questo caso, un gruppo target). Ecco perché il gruppo target deve esistere prima di creare l'autorizzazione Lambda. Per correggere questa dipendenza circolare, puoi utilizzare una risorsa personalizzata supportata da Lambda.

Soluzione

1.    Crea un file denominato index.py che include quanto segue:

Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.

Permission is hereby granted, free of charge, to any person obtaining a copy of this
software and associated documentation files (the "Software"), to deal in the Software
without restriction, including without limitation the rights to use, copy, modify,
merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
permit 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 A
PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
SOFTWARE 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>"
    }

Nota: La funzione AWS Lambda in index.py visualizza una pagina HTML con il messaggio "Hello from Lambda!" quando viene richiamata la funzione.

2.    Aggiungi il file index.py a un file di archivio denominato website.zip.

3.    Per creare un file.zip di index.py, esegui il seguente comando:

$zip website.zip index.py

4.    Crea un file chiamato cfnresponse.py basato sul modello AWS CloudFormation su AWS GitHub.

5.    Crea un file riempito chiamato custom.py in base a quanto segue:

Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.

Permission is hereby granted, free of charge, to any person obtaining a copy of this
software and associated documentation files (the "Software"), to deal in the Software
without restriction, including without limitation the rights to use, copy, modify,
merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
permit 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 A
PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

import logging
import boto3, json, botocore
import cfnresponse
#Define logging properties for 'logging'
log = logging.getLogger()
log.setLevel(logging.INFO)
#Main Lambda function to be executed
def 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)

Nota: La funzione Lambda in custom.py esegue la chiamata all'API RegisterTargets e segnala AWS CloudFormation al termine di tale chiamata API.

6.    Aggiungi i file cfnresponse.py e ** custom.py** a un file di archivio denominato ** custom.zip**. Ad esempio:

zip custom.zip cfnresponse.py custom.py

Nota: Il file custom.py utilizza la chiamata API Boto3 RegisterTargets. Questa chiamata API registra gli obiettivi specificati con il gruppo target specificato. Per ulteriori informazioni, consulta lo snippet di Python register_targets dal sito web di Boto3. Il file cfnresponse.py contiene una funzione che invia log e notifiche ad Amazon CloudWatch e AWS CloudFormation.

7.    Crea un modello AWS CloudFormation utilizzando il seguente modello YAML:

Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.

Permission is hereby granted, free of charge, to any person obtaining a copy of this
software and associated documentation files (the "Software"), to deal in the Software
without restriction, including without limitation the rights to use, copy, modify,
merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
permit 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 A
PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

AWSTemplateFormatVersion: 2010-09-09
Description: HelloWorld Lambda function template for Application Load Balancer Lambda as target
Parameters:
  # 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-name
Resources:
  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
      - Message

8.    Trasmetti i tuoi valori per i parametri S3BucketName, Subnets, VpcId e TargetGroupName allo stack AWS CloudFormation che hai creato utilizzando il modello nel passaggio 7.

9.    Crea lo stack.

10.    Dopo aver completato tutte le chiamate API, vai alla sezione Output della consoleAWS CloudFormation e cerca il seguente messaggio:

Successfully Added Lambda(arn:aws:lambda:us-east-1:123456789:function:testLambda) as Target

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