Cloudformation Lambda with dynamodb streams between two templates

Question

I have two Cloudformation stacks. One of them defines the Dynamodb.

I want the second stack to use the Dynamodb referenced in the first stack. The second stack has a Lambda function which will receive dynamodb stream from stack 1.

How should I export and import dynamodb from one stack to another for Lambda stream consumption?

Answer 1

In the DynamoDB table stack, export the StreamArn attribute of the table. Use that as the value of the EventSourceArn to define an EventSourceMapping resource in your Lambda stack.

# DynamoDB stack
Resources:
  Table:
    Type: AWS::DynamoDB::Table
    Properties:
      StreamSpecification: 
        StreamViewType: NEW_AND_OLD_IMAGES  
      # etc.

Outputs:
  TableStreamArn:
    Value: !GetAtt Table.StreamArn
    Export:
      Name: StreamArn

# Lambda stack
Resources:
  Function:
    Type: AWS::Lambda::Function
    # etc.

  EventMapping:
    Type: AWS::Lambda::EventSourceMapping
    Properties:
      EventSourceArn: !ImportValue StreamArn
      FunctionName: !GetAtt Function.Arn
      # etc.

You could also do it the other way around - import the Lambda function ARN to the DynamoDB stack and define the event mapping there, but that feels less logical to me.