Nagios is the de facto standard for open-source infrastructure monitoring, providing alerting and reporting for servers, network devices, and services. A well-configured Nagios installation gives administrators early warning of problems before they impact users.
Defining Hosts, Services, and Checks
Nagios uses a hierarchical object model where hosts contain services, and services execute check commands at defined intervals. Start by monitoring the basics: ping for host availability, disk space, CPU load, memory usage, and critical service ports. Use NRPE (Nagios Remote Plugin Executor) to execute checks on remote Linux hosts and NSClient++ for Windows servers.
Notification escalation ensures the right people are alerted at the right time. Configure first-level alerts to go to the on-call engineer via email, escalate to SMS after 15 minutes without acknowledgment, and notify the team lead after 30 minutes. This tiered approach prevents alert fatigue while ensuring critical issues receive attention.
Leverage Nagios's performance data output to feed graphing tools like RRDtool or PNP4Nagios. Historical trend data is invaluable for capacity planning and identifying gradual degradation that might not trigger threshold-based alerts. Review these trends weekly to proactively address resource constraints before they cause outages.