[Python] How to run a python script from s3 in an AWS SSM Automation Runbook using...

I have scoured the documentation from top to bottom at this point and I still can't figure out how to abstract my python scripts to s3 so I don't have to include them inline in my runbook.

I love SSM runbooks and their ability to perform logic during deployments based on parameters and branching paths, but I desperately want to abstract out my scripts. I have inline script execution down, but attached script execution is always met with this result:

Failure message Step fails when it is Poll action status for completion. Traceback (most recent call last): AttributeError: module 'test' has no attribute 'main' Handler main is not found in provided script. Please refer to Automation Service Troubleshooting Guide for more diagnosis details.

Here is the code I am trying:

description: A simple SSM runbook that calls a templated script to print and output a message.
schemaVersion: '0.3'
parameters:
Message:
type: String
description: The message to print and output.
default: "Hello from the runbook!"
mainSteps:
- name: ExecuteTemplateScript
action: aws:executeScript
isEnd: true
inputs:
Runtime: python3.10
Handler: test.main # [file].[function] format
InputPayload:
Message: '{{ Message }}'
Script: ''
Attachment: test.py # Name of the attached file
outputs:
- Name: OutputMessage
Selector: $.Payload.OutputMessage
Type: String
files:
test.py:
checksums:
sha256: 590708757b79b9438bf299ee496a121c98cf865899db8fea5d788d0cb616d1f5


I have tried variations of:

handler: test.py.main handler: test handler: test.main handler: main

Here is the test script.

#!/usr/bin/env python3
"""Simple templated script for SSM that prints and outputs a message."""

import json

def process_message(payload: dict) -> dict:
"""Process the input message and return it."""
message = payload.get('Message', 'No message provided')
print(f"Message received: {message}") # Printed to SSM logs
return {'OutputMessage': message}

def main(events, context):
"""Main function for SSM execution."""
# SSM passes InputPayload as 'events'
payload = events
result = process_message(payload)
return result # SSM captures this as output

if __name__ == "__main__":
# For local testing, simulate SSM input
import sys
if not sys.stdin.isatty():
payload = json.load(sys.stdin)
else:
payload = {'Message': 'Hello, world!'}
result = process_message(payload)
print(json.dumps(result))


Here are the docs I have tried parsing:

https://docs.aws.amazon.com/systems-manager/latest/APIReference/API_AttachmentsSource.html https://docs.aws.amazon.com/systems...tion-authoring-runbooks-scripted-example.html https://docs.aws.amazon.com/systems...utomation-document-script-considerations.html https://docs.aws.amazon.com/systems-manager/latest/userguide/automation-action-executeScript.html

The script is attached and the checksum checks out. So I have come to my last resort. Asking the experts directly. Help please.

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