A Lambda function to delete a CloudFormation Stack on Pull Request Close GitHub Event

lambda-cfn-stack-delete.py

import sys
import json
import logging

import boto3

def _get_logger():
    logger = logging.getLogger(__name__)
    logger.setLevel(logging.DEBUG)
    logger.addHandler(logging.StreamHandler(sys.stdout))
    return logger

def _delete_stack(branch_name):
    """Delete a stack if it exists for `branch_name`
    """
    logger.info('Branch is: %s', branch_name)
    
    client = boto3.client('cloudformation')
    
    logger.info('Describing stacks...')
    response = client.describe_stacks()
    
    for record in response['Stacks']:
        if record['StackName'] == branch_name:
            logger.info('Deleting stack: %s...', branch_name)
            client.delete_stack(StackName=branch_name)
            logger.info('Stack deleted')
            break
        else:
            logger.info('Stack %s does not exist. Ignoring...', branch_name)

def _process_branch(event_type, event_message):
    """Process a branch if the GitHub event is a closing of a PR.
    """
    if event_type == 'pull_request' and event_message.get('action') == 'closed':
        _delete_stack(event_message['pull_request']['head']['ref'])
    else:
        logger.info('`event_type` is not `pull_request` or `action` is not `closed`. Ignoring...')

def call(event):
    """Process a GitHub event
    
    event (dict): GitHub generated info about the current event.
    """
    logger = _get_logger()
    
    event_data = event['Records'][0]['Sns']
    event_type = event_data['MessageAttributes']['X-Github-Event']['Value']
    event_message = json.loads(event_data['Message'])
    
    _process_branch(event_type, event_message)