How to debug creating Cognito PostConfirmation trigger with SAM

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I'm not able to understand why my Cognito trigger is not firing my Lambda function. Can anyone suggest either what is wrong, or point me at a way of finding why it's not working.

I am able to trigger the function manually from the AWS console - I'm verifying this by looking at the generated log files in the console.

My SAM template looks like this:

  UserPool:
    Type: AWS::Cognito::UserPool
    Properties:
      AdminCreateUserConfig:
        AllowAdminCreateUserOnly: false
      UsernameAttributes:
        - email
      AutoVerifiedAttributes:
        - email
      Policies:
        PasswordPolicy:
          MinimumLength: 8
          RequireLowercase: true
          RequireNumbers: false
          RequireSymbols: false
          RequireUppercase: true
          TemporaryPasswordValidityDays: 90
      LambdaConfig:
        PostConfirmation: !GetAtt ConfirmUserFunction.Arn

  UserPoolInvokeConfirmUserFunctionPermission:
    Type: AWS::Lambda::Permission
    Properties:
      Action: lambda:InvokeFunction
      FunctionName: !GetAtt ConfirmUserFunction.Arn
      Principal: cognito-idp.amazonaws.com
      SourceArn: !GetAtt UserPool.Arn

  ConfirmUserFunction:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: lambdas/ConfirmUser
      Handler: app.lambda_handler
      Runtime: python3.8
      MemorySize: 128
      Timeout: 10

Have I missed something obvious?

I have also tried setting the event trigger on the lambda function, using:

      Events:
        CognitoUserPoolConfirmed:
          Type: Cognito
          Properties:
            UserPool:
              Ref: UserPool
            Trigger: PostConfirmation

This doesn't seem to make any difference at all.

I am able to successfully setup a trigger from a PostAuthentication trigger to the same Lambda, so my template can't be too far off, but I still can't see what the issue is.

aws-sam aws-sam-cli aws-lambda amazon-cognito amazon-web-services
1 Answers

@Richard,

please try the sam definition below.

userAutoConfirmFunction:
    Type: AWS::Serverless::Function
    Properties:
      Handler: src/auth/autoConfirm.handler
      Runtime: nodejs12.x
      Timeout: 10
      Description: Function to autoConfirm user.
      Events:
        CognitoEvent:
          Type: Cognito
          Properties:
            UserPool: !Ref UserPool
            Trigger: PreSignUp

UserPool:
    Type: AWS::Cognito::UserPool
    Properties:
      AdminCreateUserConfig:
        AllowAdminCreateUserOnly: false
      UserPoolName: ausavaUsers
      UsernameAttributes:
      - email
      AutoVerifiedAttributes:
      - email
      Policies:
        PasswordPolicy:
          MinimumLength: 6
          RequireLowercase: true
          RequireNumbers: false
          RequireSymbols: false
          RequireUppercase: true

This template worked for me.

user_141454210
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