In today's era where reliability and availability of IT services are crucial for any organization, monitoring systems have become an essential part of IT infrastructure. Nagios Core, an open-source solution for monitoring networks, servers, and applications, offers a flexible and scalable platform for comprehensive monitoring of IT environments. This article provides an overview of implementing and managing an extended monitoring system with Nagios Core on a Virtual private server (VPS).

I. Prerequisites and System Preparation

Before initiating the installation of Nagios Core on VPS, ensure that the server meets all system requirements. For a standard installation, it is recommended to have at least 1 GB of RAM and 20 GB of free disk space. The system should run on a Linux distribution, such as CentOS, Debian, or Ubuntu. Additionally, root access to the server is required.

II. Installation of Nagios Core

1. System Update and Installation of Necessary Packages

   Begin by updating the system and installing necessary packages for compiling Nagios Core and its plugins.

   vsudo apt-get update
   sudo apt-get upgrade
   sudo apt-get install -y build-essential libgd-dev libmcrypt-dev libssl-dev unzip apache2 php php-gd libapache2-mod-php
   

2. Download and Install Nagios Core

   Nagios Core can be downloaded from the official website. After downloading the source code, use commands to extract the archive, configure, and compile.

   cd /tmp
   wget https://assets.nagios.com/downloads/nagioscore/releases/nagios-4.4.6.tar.gz
   tar -zxvf nagios-*.tar.gz
   cd nagios-4.4.6/
   ./configure --with-httpd-conf=/etc/apache2/sites-available
   make all
   sudo make install
   sudo make install-commandmode
   sudo make install-init
   sudo make install-config
   sudo make install-webconf
   

3. User Accounts and Groups

   During the installation, create a user account nagios and a group nagcmd to allow the execution of external commands through the web interface.

   sudo useradd -m nagios
   sudo groupadd nagcmd
   sudo usermod -a -G nagcmd nagios
   sudo usermod -a -G nagcmd www-data
   

III. Installation and Configuration of Nagios Plugins

Plugins are the foundation of Nagios monitoring functionality. They provide specific checks for services, hosts, and applications.

1. Installation of NRPE (Nagios Remote Plugin Executor)

   NRPE allows executing plugins on remote hosts.

   cd /tmp
   wget https://github.com/NagiosEnterprises/nrpe/releases/download/nrpe-4.0.0/nrpe-4.0.0.tar.gz
   tar -zxvf nrpe-*.tar.gz
   cd nrpe-4.0.0/
   ./configure
   make check_nrpe
   sudo make install-plugin
   

2. Configuration of Service and Host Monitoring

   Configuration of monitored services and hosts is done by adding definitions to Nagios configuration files, usually located in /usr/local/nagios/etc/.

IV. Access to the Web Interface

After completing the installation and basic configuration, set a password for the nagiosadmin user to access the Nagios web interface.

sudo htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin

Restart the Apache server to apply the configuration changes.

sudo systemctl restart apache2

You should now be able to access the Nagios web interface via a web browser by entering your server's address, such as http://your_server/nagios.

Implementing Nagios Core on VPS is an effective way to gain insight into the status of your IT infrastructure. By adding plugins and custom scripts, monitoring can be extended and tailored to the specific needs of your organization. Regular updates and configuration reviews are crucial parts of system management to ensure that the monitoring system reflects the current state and requirements of the IT environment.