Why do I get a "Bad handler AWS Lambda - not enough values to unpack" error?

Question

I'm trying to execute a Lambda function but I get the following error:

{
  "errorMessage": "Bad handler 'AlertMetricSender': not enough values to unpack (expected 2, got 1)",
  "errorType": "Runtime.MalformedHandlerName",
  "stackTrace": []
}

My Lambda handler is specified in AlertMetricSender.py:

from modules.ZabbixSender import ZabbixSender
def lambda_handler(event, context):
    sender = ZabbixSender("10.10.10.10", 10051)
    sender.add("Zabbix server", "lambda.test", 5.65)
    sender.send()

Answer 1

This is normally caused by an incorrect value specified for the "Handler" setting for the Lambda function.

It is a reference to the method in your function code that processes events i.e. the entry point.

The value of the handler argument is comprised of the below, separated by a dot:

• The name of the file in which the Lambda handler function is located
• The name of the Python handler function.

Make sure you have not missed the filename.

In this case, it looks like the handler should be set to AlertMetricSender.lambda_handler.

Answer 2

If you're using Docker & Submodules

In my case, I'm using a custom-built docker image, and my handler is inside of a submodule.

This is what I had originally at the bottom of my Dockerfile:

ENTRYPOINT [ "python", "-m", "awslambdaric" ]
CMD ["parent_module.main.lambda_handler"]

Instead of a python-style import path (<parent_module>.<sub_module>.<function_name>), the CMD format is actually <filepath>.<function_name>. That means the parent module and child module need to be separated by a /, not a .. This is what worked for me:

ENTRYPOINT [ "python", "-m", "awslambdaric" ]
CMD ["parent_module/main.lambda_handler"]