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Nagios

A Monitoring tool for hosts and applications.

Nagios Features

  1. Infrastructure Monitoring

    • Provided by Nagios Core
    • Uses Standard protocols: ICMP,TCP,UDP,etc
    • Host Resources: Disk | CPU | Ram usage - NRPE - Addon
    • Event Handler for service Restarts across platforms: Linux | Unix | windows | etc
    • checks are performed every 5-minutes by default, unless overridden via HOST,HOSTGROUP,SERVICE,etc..
    • Active Checks and Passive Checks

  2. Modular

    • Nagios Core - Main Monitoring Engine
    • Nagios XI - Commericial Monitoring Engine
    • plugins

  3. Object Definitions

    • Hosts
    • Services - HTTP,SMTP,DNS,etc
    • Contacts - People who should me notified
    • Contact group
    • Host groups
    • Service groups
    • commands
    • Time Period - i.e when to check host-availability and when to notify etc..

  1. Optional Per-Object Monitoring schedule

  2. Scheduled Templates

  3. Host Can have parent/child dependency relationship

  4. object Inheritance

  5. Service Dependencies

  6. Varios Notification

    • SMS
    • E-mail
    • Slack Api

  7. Notification Schedules

  8. Notification States

    • Critical
    • Warning
    • Unknown
    • Ok

  9. Extensible via community Addons

    • NRPE
    • NSClient++

Installation

Features

  1. Configures required items, including Apache Httpd
  2. Auto-monitoring of localhost(127.0.0.1)

Note: Postfix or SMTP needs to be installed for e-mail configuration

Installations

  1. aptitude search nagios
  2. aptitude install nagios3
  3. dpkg -l | grep -i nagios3

Configurations

Nagios.cfg

It is the main file in the location /etc/nagios3/nagios.cfg. When nagios starts up it checks the nagios.cfg file to check the configuration.

  • 'cfg_file' - specifies config file to include: i.e hosts,services,contacts,etc..
  • 'cfg_dir' - specifies directory to include,containing config files (*.cfg) to process

Plugins

  • /etc/default/nagios3 - influences daemon-startup
  • /usr/share/nagios3/plugins - Event handlers
  • /etc/nagios-plugins - Contains pre-rolled checks
  • /usr/lib/nagios/plugins - repository of varios checks: i.e 'check_tcp','check_icmp',etc.

ICMP (PING) Monitoring

  1. Ping Monitoring using: '/usr/lib/nagios/plugins/check_host -> check_ping'
  2. Pre-defined templates to handle most monitors:
    • 'generic-host' - checks target using ICMP with sensible defaults
    • 'generic-host; - can be inherited by HOST Definition using: use generic-host
  3. Hosts and various objects are read from /etc/nagios3/conf.d.

Reloading Configurations

-  `/etc/init.d/nagios3 reload`

TCP/UDP Monitoring

Three Kinds of Remote Execution

Check By SSH

  • By default,check_by_ssh plugin is already in the plugin directory.
  • This is a direct execution on the client machines.

NRPE

  • Install NRPE agent on the hosts aptitude install nagios-nrpe-server
  • Configuration file for nrpe is /etc/nagios/nrpe.cfg and in the configutaion file add the nagios master server ip address in the allowed hosts.
  • Change the server address to "0.0.0.0" _ A NRPE Daemon will be running on all the client machines.(Linux)

NCPA

  • Cross Platform a Client side agent, no plugin required.
  • NCPA Automatically measures
    • CPU
    • Memory (Swap & RAM)
    • Network Utilization
    • Disk Utilization

Nagios At Scale, Distribute all the things

Nagios Scaling

  • Nagios forks for each service check.
  • ps -fC nagios will list multiple forks for service checks.
  • Nagios puts all the forked requested responses to the /usr/local/nagios/var/spool.

Repear Operation

  • Internal Nagios Operation
  • Grabs check results from the spool directory.
  • Serializing the processing of check results.

To scale nagios effectively, * Cheaper forking * Faster Reaping

Passive Checks

  • Eliminates forking altogether
  • Making reaping faster and less expensive

Large Scale with Mod_Gearmen

  • Uses Queuing Mechanism