This website allows visitors to comment on the content. But each comment is approved and manually published by me.
With Drupal 7, the rules module could send a notification when a new comment was saved. The module is not yet ready for production on Drupal 8.
Since this site is already monitored by Nagios, I have written an extension module that raises an alarm as soon as there are unpublished comments.
Sources on GitHub: https://github.com/ErikWegner/drupal_nagios_comments