Configuring a Nagios monitoring system on Scaleway

NagiosmonitoringApache

Reviewed on April 01, 2025

Monitoring your resources is an indispensable building block for the success of your SaaS or e-commerce application. An unnoticed system failure can have serious financial consequences and negatively impact your image. Therefore, you will learn by following this tutorial how to install and configure a Nagios monitoring application with an Apache web server to monitor your servers. It is an open-source monitoring system that can automatically alert you in case of a server dysfunction.

Before you start

To complete the actions presented below, you must have:

• A Scaleway account logged into the console
• Owner status or IAM permissions allowing you to perform actions in the intended Organization
• An SSH key
• At least 2 Instances or 2 Elastic Metal servers

Installing Nagios Core

1. Update the system and install required packages:

   sudo apt update && sudo apt upgrade -y
   sudo apt install -y wget build-essential apache2 php libapache2-mod-php php-gd libgd-dev unzip

2. Create a user and group for Nagios:

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

3. Download and extract Nagios Core:

   cd /tmp
   wget https://assets.nagios.com/downloads/nagioscore/releases/nagios-4.5.9.tar.gz
   tar -xzf nagios-4.5.9.tar.gz
   cd nagios-4.5.9

4. Compile and install Nagios Core:

   ./configure --with-nagios-group=nagios --with-command-group=nagcmd
   make all
   sudo make install
   sudo make install-commandmode
   sudo make install-init
   sudo make install-config

Installing Nagios plugins

Nagios plugins are essential for monitoring various services.

1. Install dependencies:

   sudo apt install -y libssl-dev

2. Download and extract Nagios plugins:

   cd /tmp
   wget https://nagios-plugins.org/download/nagios-plugins-2.4.11.tar.gz
   tar -xzf nagios-plugins-2.4.11.tar.gz
   cd nagios-plugins-2.4.11

3. Compile and install the plugins:

   ./configure --with-nagios-user=nagios --with-nagios-group=nagios
   make
   sudo make install

Configuring Nagios

1. Configure the Nagios web interface:

   sudo make install-webconf
   sudo a2enmod rewrite
   sudo a2enmod cgi

2. Create an administrative user for the web interface:

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

   You will be prompted to set a password for the nagiosadmin user.

3. Restart Apache to apply changes:

   sudo systemctl restart apache2

4. Verify the Nagios configuration:

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

   Ensure there are no errors before proceeding.

5. Enable and start Nagios service:

   sudo systemctl enable nagios
   sudo systemctl start nagios

Accessing the Nagios web interface

You can now access the Nagios web interface by navigating to http://your.server.ip.address/nagios in your web browser. Log in with the nagiosadmin user and the password you set earlier.

Monitoring remote servers with NCPA

The Nagios Cross-Platform Agent (NCPA) is a versatile agent that allows you to monitor remote systems. It's a modern alternative to NRPE and supports various platforms.

On the remote server:

1. Download and install NCPA:

   cd /tmp
   wget https://assets.nagios.com/downloads/ncpa3/ncpa-latest-1.amd64.deb
   sudo dpkg -i ncpa-latest-1.amd64.deb

   Adjust the download link and installation command based on your operating system. Refer to the NCPA documentation for details.

2. Edit the NCPA configuration file (typically located at /usr/local/ncpa/etc/ncpa.cfg) to set the api_token and configure allowed hosts.

3. Start and enable NCPA service:

   sudo systemctl enable ncpa_listener
   sudo systemctl start ncpa_listener

On the Nagios server

1. Download and install the NCPA plugin:

   cd /tmp
   wget https://github.com/NagiosEnterprises/ncpa/archive/v3.1.3

2. Extract the plugin and move it to the plugins directory:

   tar -xzf v3.1.3.tar.gz
   cd ncpa-3.1.3/plugins
   sudo cp check_ncpa.py /usr/local/nagios/libexec/

3. Modify permissions:

   sudo chmod +x /usr/local/nagios/libexec/check_ncpa.py

4. Define a new command in Nagios to use the NCPA plugin. Open the Nagios command configuration file:

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

   Add the following definition:

   define command {
       command_name    check_ncpa
       command_line    $USER1$/check_ncpa.py -H $HOSTADDRESS$ -t '<API_TOKEN>' -M $ARG1$
   }

   Replace <API_TOKEN> with the actual API token configured in the NCPA agent on the remote server.

5. Create a host definition for the remote server. Open the Nagios host configuration file:

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

   Add the following:

   define host {
       use         linux-server
       host_name   remote_host
       alias       Remote Host
       address     <REMOTE_SERVER_IP>
       max_check_attempts 5
       check_period 24x7
       notification_interval 30
       notification_period 24x7
   }

   Replace <REMOTE_SERVER_IP> with the actual IP address of the remote server.

6. Define a service to monitor CPU usage on the remote server using NCPA. In the same remote_host.cfg file, add:

   define service {
       use                 generic-service
       host_name           remote_host
       service_description CPU Usage
       check_command       check_ncpa!cpu/percent
   }

   You can add more services like memory usage (memory/virtual), disk usage (disk/logical/|/percent), etc.

7. Restart Nagios to apply the changes

   sudo systemctl restart nagios

Verify the setup

• Go to the Nagios web interface (http://your.server.ip.address/nagios)
• Check under Hosts to see if the remote server is listed.
• Check under Services to verify if CPU usage monitoring is working.