Boto3 Python Lambda自定义返回错误

Question

Is there a way to customise a Boto3 Lambda exception message in the form of a HTTP response and return it while also sending a forced failed?

Here is an example

except Exception as e:
  print ('\nException : failed to invoke jobs.')
  print ('Error : ' + str(e) + '\n')
  return {
    'statusCode': 500,
    'body': 'Exception : failed to invoke EMR jobs'
  }

So the customised message is now returned but the Lambda still returns a job success rather than failure.

In order to send the job failure the exception block can be changed to -

except Exception as e:
  print ('\nException : failed to invoke jobs.')
  print ('Error : ' + str(e) + '\n')
  raise

But now the custom error message has been lost.

Is there a way to combine the custom response error message and to fail the Lambda job?

Answer 1

To get the custom error message as output for the lambda, you need to actually raise the exception with the custom error message.

except Exception as e:
  custom_error = '\nException : failed to invoke jobs.\n'
  custom_error += 'Error : ' + str(e) + '\n'
  raise Exception(custom_error)

And you will get an error message like:

{
  "errorMessage": "Exception : failed to invoke jobs. ....",
  "stackTrace": [
    [
      "/var/task/lambda_function.py",
      3,
      "my_always_fails_handler",
      "raise Exception(custom_error)"
    ]
  ],
  "errorType": "Exception"
}

You can find more on the AWS documentation that you can find here Python exceptions in lambdas

Answer 2

You didn't mention it, but you're probably using AWS API Gateway to in front of your lambda.

You can use API Gateway "integration response" to transform your failed result to the HTTP response.

Here's a link to the docs