Create DynamoDB through custom resources Cloud Formation Template

Question

I am trying to create a GlobalTable in AWS DynamoDB with the below Cloud formation template script. However I am not sure if I have all things required. My Custom Resource section looks like below.

     "CreateGlobalTable":{  
      "Type":"Custom::CreateGlobalTable",
      "Properties":{  
        "ServiceToken":{  
          "Fn::GetAtt":[  
            "SolutionHelper",
            "Arn"
          ]
        },

         "GlobalTableName": "myglobaltable",
           "ReplicationGroup": [ 
              { 
                 "RegionName": "eu-west-1"
              }
           ]
      }
    },

When the stack is generated I see an entry for the same in the logs, however no Global table is created. Does it need a backing lamda function which will actually create the global table? or AWS API handles it automatically from the way it is defined above. Any guidance is much appreciated.

Answer 1

Indeed, you actually need to have a Lambda function that does the actual creation/update/deletion of the GlobalTable.

Here's a basic guidance on how to proceed:

  GlobalTableCustomResourceLambdaFunction:
    Type: AWS::Lambda::Function
    Properties:
      Handler: global_table_custom_resource.lambda_handler
      Role: !GetAtt CustomResourceRole.Arn
      Code: cloudformation/custom-resource/global_table_custom_resource.py
      Runtime: python3.6
      Timeout: '25'

  CustomResourceRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: '2012-10-17'
        Statement:
        - Sid: ''
          Effect: Allow
          Principal:
            Service: lambda.amazonaws.com
          Action: sts:AssumeRole
      Path: "/"
      Policies:
      - PolicyName: GlobalTableCustomResourceLambdaPolicy
        PolicyDocument:
          Version: '2012-10-17'
          Statement:
          - Effect: Allow
            Action:
            - dynamodb:CreateTable
            - dynamodb:UpdateTable
            - dynamodb:DeleteTable
            Resource: "*"
      ManagedPolicyArns:
      - arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole

For the Python code, I think it's beyond the scope of a StackOverflow answer, I'll refer you to this article which goes through the whole process: https://serverlesscode.com/post/python-custom-resource-cloudformation/ .