Send emails when systemd units fail

notify-failed.py

#! /usr/bin/env python3
"""Notify admins about failed services."""

from argparse import ArgumentParser, Namespace
from pathlib import Path
from typing import Iterator, List

from configlib import loadcfg
from emaillib import EMail, Mailer


DESCRIPTION = __doc__
CONFIG_FILE = Path('/usr/local/etc/notify-failed.conf')
SUBJECT = '[Service failure]: {}'
BODY = '''Dear Administrator,

the service unit "{}" has failed just now.
Please look into it.

Kind regards,

The Server
'''


def get_args() -> Namespace:
    """Parses the command line arguments."""

    parser = ArgumentParser(description=DESCRIPTION)
    parser.add_argument('unit', help='unit that failed')
    return parser.parse_args()


def get_emails(unit, sender, recipients: List[str]) -> Iterator[EMail]:
    """Yields emails."""

    for recipient in recipients:
        yield EMail(SUBJECT.format(unit), sender, recipient,
                    plain=BODY.format(unit))


def main():
    """Send emails to admins."""

    args = get_args()
    config = loadcfg(CONFIG_FILE)
    recipients = config.get('email', 'recipients').split()
    emails = get_emails(args.unit, config.get('email', 'from'), recipients)
    mailer = Mailer(
        config.get('email', 'host'), config.getint('email', 'port'),
        config.get('email', 'user'), passwd=config.get('email', 'passwd')
    )
    mailer.send(emails)


if __name__ == '__main__':
    main()