Nagios is a widely used open source tool for monitoring server and network performance.Many IT professional consider Nagios to be the most cost-effective and customisable server monitoring tool, and appreciate being able to benefit from the support of its user community.
However, one of the biggest obstacles is getting past the initial setup phase. Nagios can be complicated to install, set up, and configure. Once this is done, the tool offers metrics to monitor server performance, remediate services, and reporting.
The free Nagios Core version has some limits on it’s monitoring capabilities, unlike Nagios XI, which is a commercial tool with additional features.
If you are comfortable setting up your own custom dashboards, and have time to learn and master everything Nagios has to offer, it can very well be the best solution for monitoring your Moodle (or other) servers.