The event source and function provided mapping already exists. Please update or delete the existing mapping with UUID

[MatteoGioioso]

Description:
I am trying to implement Dynamodb streams and a trigger for lambda

 myFunction:
    Type: AWS::Serverless::Function
    Properties:
      Policies:
        - AWSLambdaBasicExecutionRole
        - DynamoDBCrudPolicy:
            TableName: !Ref TableName
        - DynamoDBStreamReadPolicy:
            TableName: !Ref TableName
            StreamName:
              !Select
                - 2
                - !Split
                  -  "/"
                  - Fn::ImportValue:
                      !Sub ${TableName}-streams-arn
      CodeUri: bin/
      Handler: myFunctions
      Events:
        dynamodb:
          Type: DynamoDB
          Properties:
            Stream:
              Fn::ImportValue: !Sub ${TableName}-streams-arn
            StartingPosition: LATEST
            BatchSize: 10

The first deployment was successful, however after adding the DynamoDBStreamReadPolicy and changed StartingPosition from TRIM_HORIZON to LATEST I got the following error:

The event source arn (" arn:aws:dynamodb:.../stream/... ") and function (" myFunction-...") provided mapping already exists. Please update or delete the existing mapping with UUID xxxx-xxxx-xxx-xxx (Service: AWSLambda; Status Code: 409; Error Code: ResourceConflictException; Request ID: xxxx-xxxxxxx-xxxx-xxx)

Observed result:
Error

Expected result:
Probably error, but at this point I did not find any explanation

PS: as my understanding once the event mapping is created must be replaced or deleted? If yes why it says "Please update or delete"? If now I want to change the mapping configuration do I need to remove it, deploy, add it again and redeploy?

Thanks

[elembie]

+1

[shearn89]

For future Googlers: I had this issue, and it was because there was a manually-created trigger hanging around that wasn't deleted with my stack. Using the CLI to delete by UUID, or going to SQS -> the queue -> Lambda triggers should have let me find it.

[MatteoGioioso]

Ok, this is a long standing bug with Cloudformation.
Similar happening with Kinesis and it was already spotted in 2018 on the serverless framework.
This is a minimal reproducible case with kinesis: https://github.com/MatteoGioioso/sls-event-source-mapping-bug
You just need to change startingPosition from TRIM_HORIZON to LATESTto trigger the bug.

[cli402]

Hit the issue same day trying to update the kinesis source mapping settings.

[bissli82]

Please fix, same issue here!

[myoung34]

I also ran into and fixed this by calling aws lambda list-event-source-mappings to find the orphaned mapping then aws lambda delete-event-source-mapping --uuid {uuid} to remove it

[lukaboljevic]

Sorry for commenting on an old post. I just ran into this issue.

I also ran into and fixed this by calling aws lambda list-event-source-mappings to find the orphaned mapping then aws lambda delete-event-source-mapping --uuid {uuid} to remove it

This solved the issue for me as well.

Before trying it out, I tried updating the event source mapping directly through the AWS console, but it would not let me, I would just get the same error again. The solution myoung34 recommended seems like the only viable option to solve this. To anyone who comes across this post while Googling, I recommend you try it out, at least until the bug is addressed.

[hoffa]

Thanks all for the input, very informative.

I'm able to reproduce this with a pure CloudFormation template:

Resources:
  MyTable:
    Type: AWS::DynamoDB::Table
    Properties:
      BillingMode: PAY_PER_REQUEST
      KeySchema:
        - AttributeName: MyAttribute
          KeyType: HASH
      AttributeDefinitions:
        - AttributeName: MyAttribute
          AttributeType: S
      StreamSpecification:
        StreamViewType: KEYS_ONLY
  MyFunction:
    Type: AWS::Lambda::Function
    Properties:
      Runtime: python3.8
      Handler: index.handler
      Role: !GetAtt MyFunctionRole.Arn
      Code:
        ZipFile: |
          def handler(event, context):
              return {'body': 'Hello World!', 'statusCode': 200}
  MyFunctionRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Statement:
          - Action:
              - sts:AssumeRole
            Effect: Allow
            Principal:
              Service:
                - lambda.amazonaws.com
        Version: "2012-10-17"
      ManagedPolicyArns:
        - arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole
        - arn:aws:iam::aws:policy/service-role/AWSLambdaDynamoDBExecutionRole
  MyFunctionMyTableEvent:
    Type: AWS::Lambda::EventSourceMapping
    Properties:
      EventSourceArn: !GetAtt MyTable.StreamArn
      FunctionName: !Ref MyFunction
      StartingPosition: TRIM_HORIZON

That template will deploy fine.

But as @MatteoGioioso mentioned, if you change StartingPosition from TRIM_HORIZON to LATEST and deploy again, you'll get the error:

The event source arn ([...]) and function ([...]) provided mapping already exists. Please update or delete the existing mapping with UUID [...]

[jayfry1077]

This is still occurring just happened to me today.

[jfuss]

From the original error and #1320 (comment) this is an issue with Lambda directly. SAM doesn't have much control over this and can't even detect it because we don't keep state. I will try to track down some things with Lambda and see what I can communicate back to the community here.

Updating labels (removing bug because this is a Lambda Service issue).