SLS CloudFormation Resource Depends on SLS Lambda Function Issue

Serverless Framework
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I am providing Cognito the permission to invoke lambda functions via lambda triggers (https://docs.aws.amazon.com/cognito/latest/developerguide/cognito-user-identity-pools-working-with-aws-lambda-triggers.html)

I have a very basic resource created in serverless.yml:

    UserPoolLambdaInvokePermission:
      Type: AWS::Lambda::Permission
      Properties:
        Action: lambda:invokeFunction
        Principal: cognito-idp.amazonaws.com
        FunctionName: arn:aws:lambda:${self:provider.region}:#{AWS::AccountId}:function:${self:service}-${self:provider.stage}-cognitoCustomMessage
        SourceArn: arn:aws:cognito-idp:${self:provider.region}:#{AWS::AccountId}:userpool/${self:provider.environment.USER_POOL_ID}

The above allows Cognito to invoke my cognitoCustomMessage lambda:

cognitoCustomMessage:
  handler: src/main/lambdas/users_handler.cognitoCustomMessage

The error message I am receiving above is: An error occurred: CognitoCustomMessageLambdaFunction - Function not found: arn:aws:lambda:us-west-2:1234567890:my-service-dev-cognitoCustomMessage (Service: AWSLambdaInternal; Status Code: 404; Error Code: ResourceNotFoundException; Request ID: e2a98525-5090-4d0f-a1f5-20610474f93b).

If I insert a DependsOn into the above resource like so:

    UserPoolLambdaInvokePermission:
      Type: AWS::Lambda::Permission
      DependsOn: arn:aws:lambda:${self:provider.region}:#{AWS::AccountId}:function:${self:service}-${self:provider.stage}-cognitoCustomMessage
      Properties:
        Action: lambda:invokeFunction
        Principal: cognito-idp.amazonaws.com
        FunctionName: arn:aws:lambda:${self:provider.region}:#{AWS::AccountId}:function:${self:service}-${self:provider.stage}-cognitoCustomMessage
        SourceArn: arn:aws:cognito-idp:${self:provider.region}:#{AWS::AccountId}:userpool/${self:provider.environment.USER_POOL_ID}

The error message I am receiving from above is: The CloudFormation template is invalid: Template format error: DependsOn must be a string or list of strings.

If I hardcode (which I don’t want to) the entire ARN of the lambda function, I get the following error: The CloudFormation template is invalid: Template format error: Unresolved resource dependencies [arn:aws:lambda:us-west-2:1234567890:function:my-service-dev-cognitoCustomMessage] in the Resources block of the template

Has anyone else run into a similar error or figured out an elegant workaround?

1 Like
2

found the solution, use dependOn property and get the function name from .serverless/serverless-state.json