Check for letsencrypt/certbot certificates expiry date. Can be run in a cron

certcheck.py

#!/usr/bin/env python3

"""
Usage: certcheck.py host1 host2 hostN. Will exit with status code 1 if any of the hosts is about to expire (see
WARNING_DAYS below).
"""

from datetime import datetime
import socket
import ssl
import sys

WARNING_DAYS = 7


def certificate_about_to_expire(host, port=443):
    conn = ssl.create_default_context().wrap_socket(socket.socket(socket.AF_INET), server_hostname=host)
    conn.connect((host, port))
    expiry_date = datetime.utcfromtimestamp(ssl.cert_time_to_seconds(conn.getpeercert()['notAfter']))
    return (expiry_date - datetime.now()).days <= WARNING_DAYS


def main(hosts):
    hosts_about_to_expire = list(filter(certificate_about_to_expire, hosts))

    if hosts_about_to_expire:
        print("The following hosts are about to expire:")
        print('\n'.join(hosts_about_to_expire))
        sys.exit(1)


if __name__ == '__main__':
    main(sys.argv[1:])