AWS Cloudformation

Question

Hi, I need help in fixing the template. This is snippet of cloudformation template.
Its creating the folder in the s3 bucket - datasource as required but Custom::S3CustomResource is stuck in CREATE_IN_PROGRESS. Please let know if there is a solution.

```
  S3CustomResource:
    Type: Custom::S3CustomResource
    Properties:
      ServiceToken: !GetAtt AWSLambdaFunction.Arn
      the_bucket: !Sub 'pe-ftv-${Environment}-dms-s3buckets'
  AWSLambdaFunction:
    Type: "AWS::Lambda::Function"
    Properties:
      FunctionName: !Sub 'pe-ftv-${Environment}-lambda'
      Handler: index.handler
      Role: !GetAtt AWSLambdaExecutionRole.Arn
      Timeout: 5
      Runtime: python3.9
      Code:
        ZipFile: |
          import boto3
          import cfnresponse
          def handler(event, context):
            bucket_name = event['ResourceProperties']['the_bucket']
            s_3 = boto3.client('s3')
            directory_name = "datasource"
            s_3.put_object(Bucket= bucket_name, Key=(directory_name+'/'))
            cfnresponse.send(event,
                                   context,
                                   cfnresponse.SUCCESS)
            return
```

MassimilianoAWS · Answer

Is this a concrete use case or just an example to test Custom Resources? If this is a concrete use case, can you explain why do you need to create a directory in the bucket? With Amazon S3 folders are just determined implicitly from the keys of the objects you store. If you store an object with key `alfa/beta/gamma.txt` in an empty bucket when browsing the S3 bucket you will see `alfa` and `beta` represented as folders.

Regarding your question, the Cloud Formation stack might get stuck because your customer resource lambda code contains an error and does not return the proper failure message to CloudFormation (see https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/cfn-lambda-function-code-cfnresponsemodule.html)

Steve Kinsman · Answer

BTW writing custom resources in Python is made much easier by using https://github.com/aws-cloudformation/custom-resource-helper.  See also https://aws.amazon.com/blogs/infrastructure-and-automation/aws-cloudformation-custom-resource-creation-with-python-aws-lambda-and-crhelper/.

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