CONTINUAL INTEGRATION

Problem scenario
You have Nagios core installed on a server in AWS.  You want a new AWS RedHat Enterprise Linux server to have the NRPE agent.  You want thorough directions for this process to potentially automate it.  How do you install and configure the NRPE agent on a RHEL server and configure a Nagios core server to monitor it?

Solution
Prerequisites

1. You need to know the internal IP address of 1) the Nagios core server; for RHEL 7.x, use ifconfig. 2) the server that will receive the NRPE agent. 
2. The AWS Security Group must have a certain rule configured for Nagios to perform ping tests.  We suggest you go to Security Groups.  Go to Inbound Rules and click "Edit."  Click "Add Rule."  For type use "ALL ICMP - IPv4." For "Source" keep it at Custom.  For the blank field use this (where x.x.x.x is the internal IP address of the Nagios core server):  x.x.x.x/32

Method
#1  (Done from Nagios client; the server destined to have the NRPE agent.)   Below is the content of a script.  You must change the x.x.x.x to the IP address of the Nagios core server.  Then run the script below on the server that you want to have the NRPE agent installed and configured on. (To run it you might run a command like this sudo bash /tmp/install.sh.)

# Script written by continualintegration.com
#!/bin/bash

yum -y update

yum -y install https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm

yum -y install nrpe nagios-plugins-users nagios-plugins-load nagios-plugins-swap nagios-plugins-disk nagios-plugins-procs

cd /etc/nagios
cp nrpe.cfg nrpe.cfg.bak
cat nrpe.cfg.bak | sed -e 's/allowed_hosts=127.0.0.1,::1/allowed_hosts=x.x.x.x/g' > nrpe.cfg
# The old way of doing the above command required perl. Here it is:
# perl -i -pe 's/.*/allowed_hosts=x.x.x.x/ if $.==81' nrpe.cfg
​# /etc/nagios/nrpe.cfg has an allowed_hosts stanza
# This setting can support multiple Nagios core servers.  The IP addresses should be separated by a comma if you have more than one.

systemctl restart nrpe
systemctl enable nrpe

# Last line of script

#2 (Done from Nagios core server)  vi /usr/local/nagios/etc/servers/contint.cfg
The content below is what you'll need for this contint.cfg file.  You just have to change three parts:

i) Replace y.y.y.y with the IP address printed at the end of the script of #3 (the internal IP address of the RHEL server to get the NRPE agent).

ii) Replace the "contint" in every spot below with the hostname found in step #3.

# RedHat Linux Host configuration file.  (Largely taken from https://www.howtoforge.com/tutorial/ubuntu-nagios/)
# You can create other .cfg files with unique names in the same directory /usr/local/nagios/etc/servers/

define host {
        use                          linux-server
        host_name                    contint
        alias                        contint
        address                      y.y.y.y
        register                     1
}

define service {
      host_name                       contint
      service_description             PING
      check_command                   check_ping!100.0,20%!500.0,60%
      max_check_attempts              2
      check_interval                  2
      retry_interval                  2
      check_period                    24x7
      check_freshness                 1
      contact_groups                  admins
      notification_interval           2
      notification_period             24x7
      notifications_enabled           1
      register                        1
}

define service {
      host_name                       contint
      service_description             Check Users
      check_command           check_local_users!20!50
      max_check_attempts              2
      check_interval                  2
      retry_interval                  2
      check_period                    24x7
      check_freshness                 1
      contact_groups                  admins
      notification_interval           2
      notification_period             24x7
      notifications_enabled           1
      register                        1
}

define service {
      host_name                       contint
      service_description             Local Disk
      check_command                   check_local_disk!20%!10%!/
      max_check_attempts              2
      check_interval                  2
      retry_interval                  2
      check_period                    24x7
      check_freshness                 1
      contact_groups                  admins
      notification_interval           2
      notification_period             24x7
      notifications_enabled           1
      register                        1
}

define service {
      host_name                       contint
      service_description             Check SSH
      check_command                   check_ssh
      max_check_attempts              2
      check_interval                  2
      retry_interval                  2
      check_period                    24x7
      check_freshness                 1
      contact_groups                  admins
      notification_interval           2
      notification_period             24x7
      notifications_enabled           1
      register                        1
}

define service {
      host_name                       contint
      service_description             Total Process
      check_command                   check_local_procs!250!400!RSZDT
      max_check_attempts              2
      check_interval                  2
      retry_interval                  2
      check_period                    24x7
      check_freshness                 1
      contact_groups                  admins
      notification_interval           2
      notification_period             24x7
      notifications_enabled           1
      register                        1
}

#3 (Done from Nagios core server) 
Run this command:
sudo /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg

If an error is found in the output, correct the problem.  If zero errors are found, proceed to step #4.

#4  (Done from Nagios client; the server destined to have the NRPE agent.) 
Run these commands:

sudo systemctl restart nrpe
sudo systemctl enable nrpe

#5  (Done from Nagios core server) 
Run these commands:

sudo systemctl restart httpd
sudo systemctl restart nagios

Problem scenario
You have a small AWS server (e.g., t2.micro with 1 GB of RAM) running RedHat Enterprise Linux.  How do you install Nagios on it?  You want thorough directions to install and configure the Nagios monitoring server on RHEL.

Solution
As root or a sudoer user, run a script with the following content:

# Written by continualintegration.com
​# This script installs Nagios.  There is some interactive portion at the beginning.  
# But it should be easy to install Nagios using the following.
# read in password for nagiosadmin
echo "Ensure you have a security group rule to allow inbound connections over port 80 from the IP address of the desktop that will access Nagios."
echo "********************************"
echo "Next..."
echo "Please enter the email address that will be sent a message when Nagios sends an alert: "
read youremail
echo "********************************"
echo "Next..."
echo "Please enter the password for nagiosadmin.  Remember that this password will sent be over the internet.  It will pass over plaintext if you follow this script.  This script is for educational and/or testing purposes.  It is advisable to use SSL for your Nagios instance (and its authentication).  The nagiosadmin user is an interactive user that logs in via a web browser.
***  Enter any password you want and press enter:"
read -s npass

yum -y update
yum -y install wget build-essential httpd php gcc glibc-common gd make net-snmp openssl-devel xinetd unzip sendmail php-gd 

useradd nagios
groupadd nagcmd
usermod -a -G nagcmd nagios
usermod -a -G nagios,nagcmd apache
cd /opt
wget https://assets.nagios.com/downloads/nagioscore/releases/nagios-4.3.1.tar.gz
tar -xzf nagios*.tar.gz
cd nagios-4.3.1

./configure --enable-command-args --with-nagios-user=nagios --with-nagios-group=nagios --with-ssl=/usr/bin/openssl --with-ssl-lib=/usr/lib/x86_64-linux-gnu

make all
make install
make install-commandmode
make install-init
make install-config
make install-webconf
cd /opt
wget https://nagios-plugins.org/download/nagios-plugins-2.2.1.tar.gz
tar -xzf nagios-plugins*.tar.gz
cd nagios-plugins-2.2.1
./configure --with-nagios-user=nagios --with-nagios-group=nagios --with-openssl
make
make install
service xinetd restart
cd /usr/local/nagios/etc/
cp nagios.cfg nagios.cfg.bak
perl -i -pe 's/.*/cfg_dir=\/usr\/local\/nagios\/etc\/servers/ if $.==51' nagios.cfg
mkdir -p /usr/local/nagios/etc/servers

sed -i -e 's/nagios@localhost/$youremail/g' /usr/local/nagios/etc/objects/contacts.cfg
htpasswd -b -c /usr/local/nagios/etc/htpasswd.users nagiosadmin $npass

systemctl start nagios.service
#systemctl restart httpd.service # we leave this commented out purely as a reference
chkconfig nagios on
systemctl start nagios.service
echo "The error 'Failed to start nagios.service: Unit not found.' may be ignorable."
echo "You should be ready to open a web browser.  Use the external AWS IP address of the server in a URL like this: "
echo "http://x.x.x.x/nagios (where x.x.x.x is the external IP address of the AWS server)"

Problem scenario
You want the Nagios Core server to monitor another AWS server.  How do you install and configure the NRPE agent on Ubuntu?

Solution
Follow these step-by-step directions if you are using AWS.  If the servers are not in AWS, the directions below may still work. These directions assume that the Nagios core server is running on Ubuntu in AWS. (If you want to know how to set up Nagios core on Ubuntu, see this posting.)  These directions also assume you have root access to the Ubuntu servers in AWS.

#1 (Done from Nagios core server) Obtain the internal IP address of the Nagios core server.  You do this by going to the back end of the Nagios server and issuing ifconfig.

#2 (Done from Nagios client; the server destined to have the NRPE agent.) Run this command on the Ubuntu server you want to be monitored by the Nagios core server:
sudo su -

#3 (Done from Nagios client; the server destined to have the NRPE agent.) Launch a script with this as the content where x.x.x.x is the IP address obtained in step #1.

apt-get -y update
apt-get -y install nagios-nrpe-server nagios-plugins
cd /etc/nagios/
cp nrpe.cfg nrpe.cfg.bak
cat nrpe.cfg.bak | sed -e 's/allowed_hosts=127.0.0.1/allowed_hosts=x.x.x.x/g' > nrpe.cfg
# The line above used to require perl as shown below:
#perl -i -pe 's/.*/server_address=x.x.x.x/ if $.==44' nrpe.cfg
​# /etc/nagios/nrpe.cfg has an allowed_hosts stanza
# This setting can support multiple Nagios core servers.  The IP addresses should be separated by a comma if you have more than one.

service nagios-nrpe-server restart
i=$(ifconfig | grep Bcast | awk '{FS=":"; print $2}' | grep -o '[.,0-9]*')
echo "Go back to the Nagios core server to monitor $i."
h=$(hostname)
echo "Also know that the hostname of this server to get the NRPE agent is $h"

#4 (Done from Nagios core server)  vi /usr/local/nagios/etc/servers/contint.cfg
The content below is what you'll need for this contint.cfg file.  You just have to change three parts:

i) Replace y.y.y.y with the IP address printed at the end of the script of #3 (the internal IP address of the Ubuntu server that will be monitored).

ii) Replace the "contint" in every spot below with the hostname found in step #3.

# Ubuntu Host configuration file.  (Largely taken from https://www.howtoforge.com/tutorial/ubuntu-nagios/)

define host {
        use                          linux-server
        host_name                    contint
        alias                                contint
        address                      y.y.y.y
        register                     1
}

define service {
      host_name                       contint
      service_description             PING
      check_command                   check_ping!100.0,20%!500.0,60%
      max_check_attempts              2
      check_interval                  2
      retry_interval                  2
      check_period                    24x7
      check_freshness                 1
      contact_groups                  admins
      notification_interval           2
      notification_period             24x7
      notifications_enabled           1
      register                        1
}

define service {
      host_name                       contint
      service_description             Check Users
      check_command           check_local_users!20!50
      max_check_attempts              2
      check_interval                  2
      retry_interval                  2
      check_period                    24x7
      check_freshness                 1
      contact_groups                  admins
      notification_interval           2
      notification_period             24x7
      notifications_enabled           1
      register                        1
}

define service {
      host_name                       contint
      service_description             Local Disk
      check_command                   check_local_disk!20%!10%!/
      max_check_attempts              2
      check_interval                  2
      retry_interval                  2
      check_period                    24x7
      check_freshness                 1
      contact_groups                  admins
      notification_interval           2
      notification_period             24x7
      notifications_enabled           1
      register                        1
}

define service {
      host_name                       contint
      service_description             Check SSH
      check_command                   check_ssh
      max_check_attempts              2
      check_interval                  2
      retry_interval                  2
      check_period                    24x7
      check_freshness                 1
      contact_groups                  admins
      notification_interval           2
      notification_period             24x7
      notifications_enabled           1
      register                        1
}

define service {
      host_name                       contint
      service_description             Total Process
      check_command                   check_local_procs!250!400!RSZDT
      max_check_attempts              2
      check_interval                  2
      retry_interval                  2
      check_period                    24x7
      check_freshness                 1
      contact_groups                  admins
      notification_interval           2
      notification_period             24x7
      notifications_enabled           1
      register                        1
}

#5 (Done from Nagios core server) 
Run this command:
/usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg

If an error is found in the output, correct the problem.  If zero errors are found, proceed to step #6.

#6  (Done from Nagios client; the server destined to have the NRPE agent.) 
Run this command:
sudo service nagios-nrpe-server restart

#7  (Done from Nagios core server) 
Run these commands:
sudo service apache2 restart
sudo service nagios restart

#8 Open a web browser, go to this address (where x.x.x.x is either the external IP address or the FQDN of the Nagios server):

http://x.x.x.x/nagios

You will be challenged for credentials via a pop-up. For the username, use "nagiosadmin" with no quotes. For the password, enter the password you entered when it was installing.

Problem scenario
You have a small AWS server (e.g., t2.nano with 0.5 GB of RAM) running Ubuntu.  How do you install Nagios on it?

Solution
1. As root or a sudoer user, run a script with the following content (sudo bash /tmp/install.sh):

# Written by continualintegration.com
​#This script installs Nagios.  There is some interactive portion at the beginning.  
# But it should be easy to install Nagios using the following.
# read in password for nagiosadmin
echo "Ensure you have a security group rule to allow inbound connections over port 80 from the IP address of the desktop that will access Nagios.  You can do this when the script is running."
echo "********************************"
echo "Next..."
echo "Please enter the email address that will be sent a message when Nagios sends an alert and press Enter: "
read youremail
echo "********************************"
echo "Next..."
echo "Please enter the password for nagiosadmin.  Remember that this password will sent be over the internet.  It will pass over plaintext if you follow this script.  This script is for educational and/or testing purposes.  It is advisable to use SSL for your Nagios instance (and its authentication).  The nagiosadmin user is an interactive user that logs in via a web browser.
***  Enter any password you want and press enter:"
read -s npass

apt-get update
apt-get -y install wget build-essential apache2 php apache2-mod-php7.0 php-gd libgd-dev sendmail unzip

useradd nagios
groupadd nagcmd
usermod -a -G nagcmd nagios
usermod -a -G nagios,nagcmd www-data
cd /opt
wget https://assets.nagios.com/downloads/nagioscore/releases/nagios-4.3.1.tar.gz
tar -xzf nagios*.tar.gz
cd nagios-4.3.1
./configure --with-nagios-group=nagios --with-command-group=nagcmd
make all
make install
make install-commandmode
make install-init
make install-config
/usr/bin/install -c -m 644 sample-config/httpd.conf /etc/apache2/sites-available/nagios.conf
cp -R contrib/eventhandlers/ /usr/local/nagios/libexec/
chown -R nagios:nagios /usr/local/nagios/libexec/eventhandlers
cd /opt
wget https://nagios-plugins.org/download/nagios-plugins-2.2.1.tar.gz
tar -xzf nagios-plugins*.tar.gz
cd nagios-plugins-2.2.1
./configure --with-nagios-user=nagios --with-nagios-group=nagios --with-openssl
make
make install
cd /usr/local/nagios/etc/
cp nagios.cfg nagios.cfg.bak
perl -i -pe 's/.*/cfg_dir=\/usr\/local\/nagios\/etc\/servers/ if $.==51' nagios.cfg
mkdir -p /usr/local/nagios/etc/servers

sed -i -e 's/nagios@localhost/$youremail/g' /usr/local/nagios/etc/objects/contacts.cfg
a2enmod rewrite
a2enmod cgi
htpasswd -b -c /usr/local/nagios/etc/htpasswd.users nagiosadmin $npass
ln -s /etc/apache2/sites-available/nagios.conf /etc/apache2/sites-enabled/

#service apache2 restart # we leave this commented out purely as a reference
telinit u # this is plan b
systemctl enable /run/systemd/generator.late/nagios.service
service nagios start
echo 'run sudo service apache2 restart'

2. Verify the installation with this command: sudo /usr/local/nagios/bin/nagios --version

3. Open a web browser, go to this address (where x.x.x.x is either the external IP address or the FQDN of the Nagios server):

http://x.x.x.x/nagios

You will be challenged for credentials via a pop-up. For the username, use "nagiosadmin" with no quotes. For the password, enter the password you entered when it was installing.