The main missing category I noticed was monitoring. Host and service monitoring are critical to maintaining stable systems, so it's a glaring oversight to exclude it. Some common solutions for monitoring are Nagios, Icinga, and Sensu.

Oddly enough, the author mentions Nagios under the Logging heading. Nagios does offer a log server product, but it's not commonly used and when someone says Nagios, they almost always mean the monitoring solution.