Introduction
Nagios is an open-source continuous monitoring tool used to monitor network devices, applications, printers, and servers. Nagios Core provides powerful monitoring capabilities and can scale to monitor thousands of hosts and services efficiently.
Architecture
- Nagios Server: Installed on the main host, runs the monitoring engine.
- Remote Hosts: Servers or devices being monitored.
- NRPE (Nagios Remote Plugin Executor): Installed on remote servers to execute monitoring plugins.
- Plugins: Scripts that collect metrics such as CPU, memory, disk usage.
- Scheduler: Executes plugins and collects monitoring data.
What You Can Monitor
- Server resources (CPU, memory, disk usage)
- System logs and running services
- Network services (HTTP, FTP, SMTP, SSH)
- Applications and databases
- Network devices like routers and switches
Key Features
- Powerful Monitoring Engine: Can monitor thousands of hosts and services.
- Fast Alerting System: Sends alerts via email or notifications immediately after detecting issues.
- Custom Plugins: Supports plugins written in shell script, Python, PHP, etc.
- Flexible Configuration: Highly customizable monitoring setup.
- Scalable: Suitable for small to enterprise environments.
Check Types
- Active Check: Nagios executes plugins on a schedule and actively connects to remote services to check status.
- Passive Check: Remote hosts or external applications send status information back to Nagios.
Nagios Directory Structure
nagios/ ├── bin - Contains the main Nagios daemon binary ├── etc - Contains all configuration files ├── libexec - Contains plugins used for monitoring ├── sbin - Contains CGI executables for web interface ├── share - Contains web interface HTML and PHP files └── var - Contains runtime data, logs, and object definitions
Important Configuration Files
- nagios.cfg: Main configuration file defining global settings and locations of other configuration files.
- resource.cfg: Stores sensitive information such as usernames and passwords securely.
- contacts.cfg: Defines users and groups who receive alerts and notifications.
- commands.cfg: Defines commands used for service checks, notifications, and event handlers.
- templates.cfg: Defines reusable templates for hosts, services, and contacts.
- timeperiods.cfg: Defines valid monitoring and notification time periods like 24x7 or work hours.
etc Directory Important Files
- .htpasswd: Secures the web interface by storing login credentials.
- cgi.cfg: Controls web interface access and permissions.
- resource.cfg: Stores credentials and sensitive configuration data.
- objects directory: Contains definitions of hosts, services, contacts, and commands.
Monitoring Workflow
Nagios Scheduler → Executes Plugin → Plugin Collects Data → Returns Status → Nagios Processes Result → Sends Alert if Issue Found