At a Glance:
Nagios is a C-based host, service, and network monitoring program that uses a plugin interface for user-defined checks, supports parent host hierarchies, and provides an optional web interface for viewing status and history.
Overview:
Nagios is a monitoring program for hosts, services, and networks. It is designed to monitor network services via protocols like SMTP, POP3, HTTP, and PING, and to check host resources such as processor load and disk usage. The program can define network host hierarchies to distinguish between down and unreachable hosts. Notifications for problem events and their resolution can be delivered through email, pager, or user-defined methods. It includes an optional web interface for viewing current status, history, and logs, and supports an interface for user-developed service monitoring plugins.
Key Decision Points:
Plugin Architecture: Service monitoring methods are fully extensible through a documented plugin interface, so custom checks can be developed.
Network Topology Definition: A “parent” host hierarchy can be defined, which allows the system to distinguish between hosts that are truly down and those that are simply unreachable due to an upstream outage.
Notification Channels: Problem alerts and recovery notifications are supported via email and pager, with the option to define custom notification methods.
Web Interface is Optional: A CGI-based web interface is provided for viewing status, history, and logs, but its use is not mandatory for the core monitoring engine.
Core Features:
Network Service Monitoring: Checks network services using standard protocols such as SMTP, POP3, HTTP, and ICMP PING.
Host Resource Monitoring: Monitors local host metrics, including processor load and disk usage.
Parent Host Hierarchy: Recognizes network dependencies to correctly report whether a host is down or unreachable.
User-Developed Plugin Support: Allows custom service monitoring methods to be added via a defined plugin interface.
Event-Driven Notifications: Sends alerts when problems are detected and resolved through configurable channels including email and pager.
Event Handlers: Supports the definition of event handlers that can be triggered to take proactive actions in response to problems.
Use Cases:
System administrators monitoring the availability of critical network services such as web servers, mail servers, and basic host connectivity.
Operators who need to receive immediate alerts about infrastructure problems and their resolution through pager or email.
Developers or administrators who need to integrate custom monitoring logic for specific applications or services using the plugin interface.
Open-Source Alternative Value:
Nagios provides a monitoring framework that allows for the direct use and modification of its C-based source code under the GPLv2 license. The plugin interface is an open specification, which gives developers the ability to create service checks for specific internal needs without depending on a closed ecosystem. Its structural approach to host dependencies offers a specific method for managing alert clarity in environments with layered network topologies.
