Automatic certbot renewal

# Content of /etc/systemd/system/certbot.service:

[Unit]
Description=Let's Encrypt renewal

[Service]
Type=oneshot
ExecStart=/usr/bin/certbot renew --quiet --agree-tos
ExecStartPost=/bin/systemctl reload apache2

# Content of /etc/systemd/system/certbot.timer:

[Unit]
Description=Monthly renewal of Let's Encrypt's certificates

[Timer]
OnCalendar=*-*-1,15 00:00:00
RandomizedDelaySec=1day
Persistent=true

[Install]
WantedBy=timers.target

# Commands after file creations:
# systemctl enable certbot.timer
# systemctl start certbot.timer