How can I get the name of the lambda function that raised error with DLQ?

Question

LambdaA is a function that raises an error.

```
import json

def lambda_handler(event, context):
    raise Exception("ERROR!!")
    return {
        'statusCode': 200,
        'body': json.dumps('Hello from Lambda!')
    }
```

LambdaB is a function that prints "event".

```
import json

def lambda_handler(event, context):
    print(f"Event: {event}")
    return {
        'statusCode': 200,
        'body': json.dumps('Hello from Lambda!')
    }

```

The SNS topic "TestTopic" is set as Dead-letter queue service in the LambdaA .  
"TestTopic" is subscribed by LambdaB.
![dlq](/media/postImages/original/IMDUyvH_EPR1CipIPGWXWg9g)

I invoked LambdaA asynchronously and checked the CloudWatch logs for LambdaB.  
And then "event" dose not seem to contain the function name that caused the error.

> Event: {'Records': [{'EventSource': 'aws:sns', 'EventVersion': '1.0', 'EventSubscriptionArn': 'arn:aws:sns:ap-northeast-1:xxxxxxxxxxxx:TestTopic:xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx', 'Sns': {'Type': 'Notification', 'MessageId': 'xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx', 'TopicArn': 'arn:aws:sns:ap-northeast-1:xxxxxxxxxxxx:TestTopic', 'Subject': None, 'Message': '{}', 'Timestamp': '2024-03-15T10:26:25.862Z', 'SignatureVersion': '1', 'Signature': 'xxxxxxxxxxxxxxxxxxx', 'SigningCertUrl': 'https://sns.ap-northeast-1.amazonaws.com/SimpleNotificationService-xxxxxxxxxxxxxxxxxxxx.pem', 'UnsubscribeUrl': 'https://sns.ap-northeast-1.amazonaws.com/?Action=Unsubscribe&SubscriptionArn=arn:aws:sns:ap-northeast-1:xxxxxxxxxxxx:TestTopic:xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx', 'MessageAttributes': {'RequestID': {'Type': 'String', 'Value': 'xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx'}, 'ErrorCode': {'Type': 'String', 'Value': '200'}, 'ErrorMessage': {'Type': 'String', 'Value': 'ERROR!!'}}}}]}

How can I get the function name?

Accepted Answer

Hi,

AWS Lambda does not include the function name in the attributes that are added to the event, see https://docs.aws.amazon.com/lambda/latest/dg/invocation-async.html#invocation-dlq

> Lambda sends the event to the dead-letter queue as-is, with additional information in attributes. You can use this information to identify the error that the function returned, or to correlate the event with logs or an AWS X-Ray trace.
>
> **Dead-letter queue message attributes**
>
 > **RequestID (String)** – The ID of the invocation request. Request IDs appear in function logs. You can also use the X-Ray SDK to record the request ID on an attribute in the trace. You can then search for traces by request ID in the X-Ray console. For an example, see the error processor sample.
>
> **ErrorCode (Number)** – The HTTP status code.
>
> **ErrorMessage (String)** – The first 1 KB of the error message.

However, you could implement such logic in your exception handling logic in your Lambda function. Alternatively, you could use a 1:1 mapping between SNS topics and Lambda functions, that way it would always be clear from which function the message originated.

Regards,
Ben

Answer

Thank you for your answer. I understood your answer.
I also want to catch timeout and throttling, so I will try 1:1 mapping between SNS topics and Lambda functions.

Best regards, yyahi

How can I get the name of the lambda function that raised error with DLQ?

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