Lambda CloudWatch Log Retention Manager

LogRetainManager.py

import boto3
import os

def lambda_handler(event, context):
  default_region = os.environ.get('AWS_REGION', 'us-east-1')
  retain_days = int(os.environ.get('RETAIN_DAYS', '30'))
  
  session = boto3.Session()
  client = session.client('ec2', region_name=default_region)

  for region_dict in client.describe_regions()['Regions']:
    region = region_dict['RegionName']
    print('Region:', region)
    logs = session.client('logs', region_name=region)
    log_groups = logs.describe_log_groups()

    for log_group in log_groups['logGroups']:
        log_group_name = log_group['logGroupName']
        if 'retentionInDays' in log_group:
          print(region, log_group_name, log_group['retentionInDays'], 'days')        
        else:
          print(region, log_group_name, retain_days, 'days **PUT**')        
          response = logs.put_retention_policy(
            logGroupName=log_group_name,
            retentionInDays=retain_days
          )

  return 'CloudWatchLogRetention.Success'

Sample-CloudWatch-Event.json

{
    "version": "0",
    "id": "arar40ba-aaaa-bbbb-cccc-81d33314b7",
    "detail-type": "Scheduled Event",
    "source": "aws.events",
    "account": "1212121212",
    "time": "2018-10-30T10:22:22Z",
    "region": "us-east-1",
    "resources": [
        "arn:aws:events:us-east-1:1212121212:rule/logrtnmgr"
    ],
    "detail": {}
}

See blog post