CloudFormation / CustomResource / minimal Python Lambda function for logging resource update requests

minimal-custom-resource-hander.py

from __future__ import print_function

import json
import logging
import urllib2

logger = logging.getLogger()
logger.setLevel(logging.INFO)

SUCCESS = 'SUCCESS'
FAILED = 'FAILED'

def lambda_handler(event, context):
    logger.info("Received event. Full parameters: {}".format(json.dumps(event)))
 
    response = {
        "StackId": event["StackId"],
        "RequestId": event["RequestId"],
        "LogicalResourceId": event["LogicalResourceId"],
        "Status": SUCCESS,
        "Data": {
            "Test": "true"
        }
    }
    if event.get("PhysicalResourceId", False):
        response["PhysicalResourceId"] = event["PhysicalResourceId"]
    else:
        response["PhysicalResourceId"] = event["LogicalResourceId"] + "-12345"
        
    serialized = json.dumps(response)
    logger.info("Responding with: %s" % (serialized))

    req = urllib2.Request(
        event['ResponseURL'], data=serialized,
        headers={'Content-Length': len(serialized),
                 'Content-Type': ''}
    )
    req.get_method = lambda: 'PUT'

    try:
        urllib2.urlopen(req)
        logger.debug("Request to CFN API succeeded, nothing to do here")
    except urllib2.HTTPError as e:
        logger.error("Callback to CFN API failed with status %d" % e.code)
        logger.error("Response: %s" % e.reason)
    except urllib2.URLError as e:
        logger.error("Failed to reach the server - %s" % e.reason)

Based on: https://serverlesscode.com/post/python-custom-resource-cloudformation/

Specifically: https://github.com/ryansb/cfn-wrapper-python/blob/master/cfn_resource.py