Which open source monitoring tool is primarily used for server monitoring?

Nagios XI is primarily used for server monitoring because it is designed specifically to monitor the availability and performance of servers, network devices, and applications. Nagios provides comprehensive monitoring capabilities, including alerting and reporting, which are essential for identifying issues in real-time. It utilizes a plugin architecture that allows users to extend its functionality by writing their own scripts or utilizing existing ones, making it highly customizable for different monitoring needs.

While Grafana is a powerful tool for visualizing time series data and can be integrated with various data sources for dashboards, its primary function is not direct monitoring but rather displaying metrics collected by other tools. Prometheus, another popular option, is specifically designed for monitoring and alerting, especially in containerized environments, but in the context of server monitoring alone, Nagios XI has a broader focus on infrastructure monitoring. Amazon Elasticsearch Service is a managed service for indexing and searching logs and data but does not specifically serve as a monitoring tool by itself.

The unique set of features and focused purpose of Nagios XI in monitoring infrastructure makes it the preferred choice among the listed options for server monitoring tasks.