Nagios

Open Source Network Monitoring

ChrisClymer.com/articles/nagios

What Is Nagios?

• Network monitoring system
• Watches hosts and services on your network, and notifies you about problems
• Capable of resolving certain issues
• Less stress for you, the admin!

Why would I use Nagios?

• You're responsible for maintaining a network
• You don't want to spend all of your time babysitting it
• You prefer to solve problems before your bosses know they even exist
• You don't want to throw large sums of money at a poor propietary solution
• You'd like more time for drinking beer.

Installation

• Debian, Suse, Red Hat, and most other distros have packages available.
• Source is available, building from it is a bit of work

Configuration

• Lots of config files, a few that are critical
• contacts.cfg
• contactgroups.cfg
• hosts.cfg
• hostgroups.cfg
• services.cfg

contacts.cfg

• Defines who gets notifications about problems with hosts and services

define contact{
        contact_name                    nagios
        alias                           Nagios Admin
        service_notification_period     24x7
        host_notification_period        24x7
        service_notification_options    w,u,c,r
        host_notification_options       d,u,r
        service_notification_commands   notify-by-email
        host_notification_commands      host-notify-by-email
        email                           nagios@chrisclymer.com
}

contactgroups.cfg

• Defines groups of contacts who receive notifications

define contactgroup{
        contactgroup_name       admins
        alias                   Administrators
        members                 nagios
        }

hosts.cfg

• Defines the hosts that we will monitor

define host {
        use                     generic-host
        host_name               akron-web
        alias                   Akron Webserver
        address                 192.168.10.51
        parents                 akron-fw1
        check_command           check-host-alive
        max_check_attempts      20
        notification_interval   60
        notification_period     24x7
        notification_options    d,u,r
        }

hostgroups.cfg

• Defines groups for the hosts we will monitor

define hostgroup{
        hostgroup_name  akron
        alias           Akron Office
        contact_groups  admins,akron-admins
        members         akron-web,akron-mail,akron-file
        }

services.cfg

• Defines the services that we will monitor for each host

define service{
        use                             generic-service
        host_name                       akron-web
        service_description             HTTP
        is_volatile                     0
        check_period                    24x7
        max_check_attempts              3
        normal_check_interval           5
        retry_check_interval            1
        contact_groups                  akron-admins,admins
        notification_interval           240
        notification_period             24x7
        notification_options            n
        check_command                   check_http
        }

Templating

• Nagios configs can get terribly repetitve
• Solution: templates!
• All of the Nagios config files support "templating"
• templating works much like include statements in a multitude of programming languages

Template Definition

define service{
        use                             generic-service
        name                            http-service
        service_description             HTTP
        is_volatile                     0
        check_period                    24x7
        max_check_attempts              3
        normal_check_interval           5
        retry_check_interval            1
        contact_groups                  admins
        notification_interval           120
        notification_period             workhours
        notification_options            w,u,c,r
        check_command                   check_http
        register                        0
        }

Template Usage

define service{
        use                             http-service
        host_name                       akron-web
        }

Additional Configs

• escalations.cfg - defines what procedure to follow in escalating various problems
• timeperiods.cfg - defines time periods used by all of the other configs
• misccommands.cfg - defines miscellaneous custom commands, such as notifications
• checkcommands.cfg - defines your own custom Nagios check commands

Nagios Plugins

• Without plugins, Nagios is pretty useless
• Plugins are what do the actual checking of each service and host
• There are included plugins, such as check_ping, check_http, check_dns, check_pop, check_imap, check_tcp and many others.
• Plugins are easy to write! With a little effort, you can write your own custom plugin.
• There is also a large collection of community created plugins at http://nagiosexchange.org

NRPE

• NRPE is the Nagios Remote Plugin Executor
• NRPE lets you do local host checks, instead of just external ones
• NRPE runs on Linux, BSD, Solaris, and Windows
• NRPE uses the same plugins as the Nagios daemon

allowed_hosts=127.0.0.1,192.168.10.10
nrpe_user=nagios
nrpe_group=nagios
command_timeout=60
command[check_load]=/usr/nagios/libexec/check_load -w 15,10,5 -c 30,25,20
command[check_disk1]=/usr/nagios/libexec/check_disk -w 20 -c 10 -p /dev/hda1

Web Interface

• Default view
• Acknowledgements
• Mapping

This is just the beginning!

• This is a basic primer to Nagios. Its capablities are largely limited only by how imaginative you can be
• Auto-generating Nagios configs, self-mapping networks, self-healing networks, and more!
• #nagios on irc.freenode.net
• Nagios: System and Network Monitoring, Wolfgang Barth, No Starch Press