Fetch RDS log files via command line

rdsfetch.py

"""Fetch RDS log file via command line

AWS deprecated their RDS command-line utility, and the AWS CLI only includes
a subcommand for downloading portion of log file. This downloads full log
file, so that it may be analyzed in say pgbadger, for example:

    pgbadger -A 1 -a 1 -j 4 --prefix '%t:%r:%u@%d:[%p]:' \
        --log-duration --outfile postgresql.log-2017-02-09-07.html \
        postgresql.log.2017-02-09-07
"""

import boto3
import sys

rds = boto3.client('rds')

def fetch(db_instance_identifier, log_file_name):
    from os.path import basename

    marker = '0'
    with open(basename(log_file_name), 'w') as f:
        incomplete = True
        while incomplete:
            # Download portion
            response = rds.download_db_log_file_portion(
                DBInstanceIdentifier=db_instance_identifier,
                LogFileName=log_file_name,
                Marker=marker)

            # Write data to file
            f.write(response['LogFileData'])

            marker = response['Marker']
            incomplete = response['AdditionalDataPending']
            
            sys.stderr.write('.')
            
    sys.stderr.write('\n')

if __name__ == '__main__':
    fetch(sys.argv[1], sys.argv[2])