CFN Lambda backed Custom Resource to inject dynamic values

lambda-custom-resource.yml

AWSTemplateFormatVersion: "2010-09-09"
Description: Custom Ressource Tester Template

Parameters:
  ApiName:
    Type: String
    Description: Enter the appsync api name

Resources:  
  
  ApiHelperResource:
    Type: "Custom::ApiHelper"
    Properties:
      Description: |
        For a given appsync api, this resource returns `ApiId`, `ApiUrl` and `ApiKey` to be used anywhere in the template.
        This also validates that the apiKey is active for at least the next 30 days; fails deplyment otherwise.
        Input params: api_name
      ServiceToken: !GetAtt
        - ApiHelperFunction
        - Arn
      api_name: !Ref ApiName
  
  ApiHelperFunction:
    Type: "AWS::Lambda::Function"
    Properties:
      FunctionName: ApiHelperFunction
      Code:
        ZipFile: |          
          from __future__ import print_function
          import json
          import boto3
          import cfnresponse
          import datetime

          SUCCESS = "SUCCESS"
          FAILED = "FAILED"

          print('Loading function')
          appsync = boto3.client('appsync')

          def lambda_handler(event, context):
              print("Received event: " + json.dumps(event, indent=2))
              responseData={}
              try:
                  if event['RequestType'] == 'Create' or event['RequestType'] == 'Update':
                    print("Request Type:",event['RequestType'])
                    data = get_appsync_api_details(event['ResourceProperties']['api_name'])
                    responseData=data
                  elif event['RequestType'] == 'Delete':
                      print("Delete Request. No change needed.")
                  responseStatus = 'SUCCESS'
              except Exception as e:
                  print('Failed to process:', e)
                  responseStatus = FAILED
                  responseData = {'Failure': f'Something went wrong. {str(e)}'}
              cfnresponse.send(event, context, responseStatus, responseData)

          def get_appsync_api_details(api_name):
              api_list = appsync.list_graphql_apis()['graphqlApis']
              filtered_apis = list(filter(lambda api: api['name'] == api_name, api_list))
              if not filtered_apis:
                raise Exception(f'{api_name} not found.')
              api = filtered_apis[0]
              
              api_keys = appsync.list_api_keys(apiId=api['apiId'])['apiKeys']
              print(api_keys)
              api_key= api_keys[0]
              validate_apikey(api_key['expires'])
              return {
                  'ApiId': api['apiId'],
                  'ApiUrl': api['uris']['GRAPHQL'],
                  'ApiKey': api_key['id']
              }

          def validate_apikey(expires_utc):
            expires = datetime.datetime.fromtimestamp(expires_utc)
            current_time = datetime.datetime.utcnow()
            diff = (expires - current_time).days
            if diff < 30:
              raise Exception(f'Api key is going to expire in 30 days. Please renew it.')

      Handler: index.lambda_handler
      Runtime: python3.6
      Timeout: 50
      Role: !GetAtt
        - LambdaExecutionRole
        - Arn

  LambdaExecutionRole:
    Type: "AWS::IAM::Role"
    Properties:
      AssumeRolePolicyDocument:
        Version: 2012-10-17
        Statement:
          - Effect: Allow
            Principal:
              Service:
                - lambda.amazonaws.com
            Action:
              - "sts:AssumeRole"
      Policies:
        - PolicyName: lambdaPolicy
          PolicyDocument:
            Version: 2012-10-17
            Statement:
              - Effect: Allow
                Action:
                  - "logs:CreateLogGroup"
                  - "logs:CreateLogStream"
                  - "logs:PutLogEvents"
                Resource: "arn:aws:logs:*:*:*"
        - PolicyName: LambdaAppsyncPolicy
          PolicyDocument:
            Version: "2012-10-17"
            Statement:
              - Effect: Allow
                Action:
                  - appsync:*
                Resource: "*"

Outputs:
  ApiId:
    Description: ApiId value
    Value: !GetAtt ApiHelperResource.ApiId # Read output of the custom resource
  ApiUrl:
    Description: ApiUrl value
    Value: !GetAtt ApiHelperResource.ApiUrl
  ApiKey:
    Description: ApiKey value
    Value: !GetAtt ApiHelperResource.ApiKey