[cmg]

With Icinga, for webservers:

- apt status (for security/critical updates that haven't been run yet)

- reboot needed (presence of /var/run/reboot-required)

- fail2ban jail status (how many are in each of our defined jails)

- CPU usage

- MySQL active, long-running processes, number of queries

- iostat numbers

- disk space

- SSL cert expiration date

- domain expiration date

- reachability (ping, domain resolution, specific string in an HTTP request)

- Application-specific checks (WordPress, Drupal, CRM, etc)

- postfix queue size

[Eater_of_food]

First mention of [ -f /var/run/reboot-required ], which is important to ensure security updates have taken effect