Monitoring with Nagios

Network monitoring is a critical and needed function which would have a direct impact on business operations and improve the troubleshooting process. In this context, this project aims to monitor a distant linux server through customised plugins using the open source system Nagios.

What is Nagios ?

Nagios is a powerful IT infrastructure monitoring tool. It is designed to ease the work of the system administrator and organizations in general by giving them an overview of their network status.

Getting started

These instructions will get you a copy of the project up and running on your local machine for development and testing purposes.

Prerequisites

Installing

• Nagios Core 4.2.4 on the monitoring server: install-nagios.sh
• Nagios Remote Plugin Executor (NRPE) on the target and monitoring server: install-nrpe.sh
• Nagios Service Check Acceptor (NSCA) on the target and monitoring server : install-nsca.sh

Configuration

• Host definition

1. Open the main Nagios configuration file

sudo nano /usr/local/nagios/etc/nagios.cfg

2. Uncomment the following line by removing the # symbol

#cfg_dir=/usr/local/nagios/etc/servers

3. Create this directory that will store the configuration file for the target server that we will monitor

sudo mkdir /usr/local/nagios/etc/servers

4. Create the configuration file for our target server

sudo touch /usr/local/nagios/etc/servers/server.cfg

5. Write the following into this file

define host {
  use       linux-server
  host_name remote-server
  alias     remote-server
  address   Target_Server_IP
 }

Custom plugins

check_throughput: Calculate the number of received bytes per minute on an interface and corresponding throughput of received traffic.

check_interface_status: Sends an alert to the nagios server whenver the interface changes its state from UP to DOWN.

Active check: check_throughput.sh

On the target server

1. Edit the configuration file of NRPE in order to add the IP address of the Nagios server: Nagios_Server_IP

allowed_hosts=127.0.0.1,Nagios_Server_IP

2. Change to the directory containing Nagios plugins

cd /usr/lib/nagios/plugins

3. Create a new file containing the script of the plugin

sudo touch check_throughput.sh

4. Make the script executable

sudo chmod +x check_throughput.sh

5. Add the script to the NRPE configuration

sudo nano /etc/nagios/nrpe.cfg
command[check_throughput]=/usr/lib/nagios/plugins/check_throughput.sh  

6. Restart Nagios NRPE service

sudo service nagios-nrpe-server restart 

On the monitoring server

7. Verify that the check_nrpe plugin is installed correctly

ls /usr/local/nagios/libexec/check_nrpe

8. Add a new command related to the check_nrpe in the Nagios Core commands configuration file

sudo nano /usr/local/nagios/etc/objects/commands.cfg
define command {
  command_name    check_nrpe
  command_line    $USER1$/check_nrpe -H $HOSTADDRESS$ -c $ARG1$
 }

9. Define new command corresponding to our plugin in /usr/local/nagios/etc/objects/commands.cfg

define command {
  command_name        check_throughput
  command_line        $USER1$/check_nrpe -H $HOSTADDRESS$ -c check_thgroughput $ARG1$ 
 }

10. Define new service for this command in configuration file of our server: server.cfg

define service {
  use                 generic-service
  hostname            server
  service_description Throughput 
  check_command       check_throughput
  check_interval      1
  retry_interval      1
 }

11. Validate the configuration and restart the nagios core server

sudo /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg
sudo service nagios restart 

Passive check: check_interface_status.sh

On the monitoring server

1. Edit the commands.cfg file and add a definition of the following command

sudo nano /usr/local/nagios/etc/objects/commands.cfg
define command {
  command_name  check_dummy
  command_line  $USER1$/check_dummy $ARG1$ $ARG2$ 
 }

2. Edit the server.cfg file and add the following service definition

define service {
  use                     generic-service
  host_name               server
  service_description     Interface-Status  
  active_checks_enabled   0
  passive_checks_enabled  1
  check_freshness         1
  freshness_threshold     43200
  check_command           check_dummy!1!"No passive checks have been made for 12 hours" 
 }

3. Validate the configuration and restart the nagios core server

sudo /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg
sudo service nagios restart 

On the target server

4. Change to the directory containing Nagios plugins

cd /usr/lib/nagios/plugins

5. Create a new file containing the script of the plugin

sudo touch check_interface_status.sh

6. Make the script executable

sudo chmod +x check_interface_status.sh

7. Add the script to the NRPE configuration

sudo nano /etc/nagios/nrpe.cfg
command[check_interface_status]=/usr/lib/nagios/plugins/check_interface_status.sh  

8. Write a script /usr/local/sbin/nsca_interface_state.sh that reads the output of the interface_status plugin, converts it to an nsca-type service check result, and sends it to the nagios server.
9. Schedule this script to run at regular intervals using Cron

sudo crontab -e 
* * * * * /usr/local/sbin/nsca_interface_state.sh

Tests

• Access the Nagios web interface: Nagios_Server_IP/nagios
• Go to Services and you will notice that the new services we have just created have been added successfully.

Built with

• Bash programming language

Authors

• Firas Esbai - Initial work - Firas Esbai

Licence

This project is licenced under the Apache-2.0 Licence