What is Continuous Monitoring?
Continuous Monitoring is the process of continuously keeping the track of all the servers and the applications which are hosted on that server and creating a log out of it. It helps in cases when your application transition from an active to a critical state. Sometimes you are not on the application and in that caseyou can’t check whether your application is up or down. So this work is basically done by the tool which continuously monitors the application whether it is up or down. If there is any performance issues or any non-responsiveness or there is any downtime, all these are monitored by the continuous monitoring tool.
Nagios
It is open-source software that helps us in continuous monitoring applications which are running on the remote host. Nagios follows Master-Slave Architecture. There is one server on which Nagios is installed and others are basically normal systems on which applications are running. In order to interact with Nagios Server to services that are running on some other server, we have to install some plugins on that server that wants to get monitored.
Nagios Architecture
- Nagios has Master-Slave Architecture.
- Nagios is installed on a separate server i.e. Master Server and plugins are installed on the host side which needs to be monitored.
- Nagios Master Server sends a signal to Plugins of the host server.
- Plugins collect data from host server such as CPU Utilization, Core Utilized and send back to Nagios Master Server.
- Then Nagios Master Server Send Status to admin and update Nagios GUI.
Steps to Install Nagios on AWS EC2 (Centos)
Use the Below script to install Nagios
sudo su yum install httpd php -y yum install gcc glibc glibc-common -y yum install gd gd-devel -y adduser -m nagios passwd nagios groupadd nagioscmd usermod -a -G nagioscmd nagios usermod -a -G nagioscmd apache mkdir ~/downloads cd ~/downloads wget https://webwerks.dl.sourceforge.net/project/nagios/nagios-4.x/nagios-4.0.8/nagios-4.0.8.tar.gz wget http://nagios-plugins.org/download/nagios-plugins-2.0.3.tar.gz tar zxvf nagios-4.0.8.tar.gz cd nagios-4.0.8 ./configure --with-command-group=nagioscmd make all make install make install-init make install-config make install-commandmode
In order to Change Configuration such as email, contact name then edit:
vi /usr/local/nagios/etc/objects/contacts.cfg
In order to configure the web interface.
make install-webconf
First set a password for the web Interface and then restart httpd.
htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin service httpd restart
Now in order to install Nagios Plugins
cd ~/downloads tar zxvf nagios-plugins-2.0.3.tar.gz cd nagios-plugins-2.0.3 ./configure --with-nagios-user=nagios --with-nagios-group=nagios make make install chkconfig --add nagios chkconfig nagios on /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg service nagios start service httpd restart

Install Nagios on AWS EC2
Add Host & Service in Nagios
1. Copy localhost.cfg file in the server folder
cp objects/localhost.cfg servers/hosts.cfg
2. Replace IP and hostname in host.cfg file using VI editor and comment hostgroup
:%s/127.0.0.1/<Server IP> %s/localhost/durgesh
3. In nagios.cfg file add new line
cfg_file=/usr/local/nagios/etc/servers/hosts.cfg

Install Nagios on AWS EC2
If you want to add new service then you can simply add new service in “/usr/local/nagios/etc/servers/hosts.cfg”
Questions
How to change notification interval in Nagios?
In order to change host or service notification Interval, we can add notification_interval and notification_period in host and service.
Check_Swap Nagios Example?
Critical if less than 10% of swap is free, warning if less than 20% is free
define service{ use loacl-service host_name durgesh service_description Swap Usage check_command check_local_swap!20!10 }
Check_tcp Nagios Example?
Check Port 2001 is Up TCP
define service{ use loacl-service host_name durgesh service_description My application [Port 2001] check_command check_tcp!2001 }
Check_udp Nagios Example?
Check Port 2001 is Up UDP
define service{ use loacl-service host_name durgesh service_description My application [Port 2001] check_command check_udp!2001 }
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Reference :
https://assets.nagios.com/downloads/nagioscore/docs/nagioscore/4/en/quickstart.html
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