The Nagios architecture was designed keeping in mind flexibility and scalability. It consists of a central server, which is referred to as the Monitoring Server and the clients are the Nagios agents, that run on each node that needs to be monitored.

The checks can be performed for service, port, memory, disk, and so on, by using either active checks or passive checks. The active checks are initiated by the Nagios server and the passive checks are initiated by the client. Its flexibility allows us to have programmable APIs and customizable plugins for monitoring.

Nagios is an enterprise class monitoring solution, which can manage a large number of nodes. It can be scaled easily, and it has the ability to write custom plugins for your applications. Nagios is quite flexible and powerful, and it supports many configurations and components.

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Let's look at the installation of Nagios, and how we can set it up. The following steps are for Rhel, CentOS, Fedora, and Ubuntu:

Let's start with the configuration.

Navigate to the directory, where the package was downloaded. The downloaded package could be either in the Downloads folder or in the present working directory.

$ tar zxvf nagios-4.0.8.tar.gz
$ cd nagios-4.0.8/
$ ./configure –with-command-group=nagcmd

$ make all; sudo make install; sudo make install-init
$ sudo make install-config; sudo make install-commandmode

If you see a message, such as Return code of 127 is out of bounds – plugin may be missing on the right panel, then this means that your configuration is correct as of now. This message indicates that the Nagios plugins are missing, and we will show you how to install these plugins in the next step.

Nagios provides many useful plug-ins to get us started with monitoring all the basics. We can write our custom checks and integrate it with other plug-ins, such as check_disk, check_load, and many more. Download the latest stable version of the plugins and then extract them. The following command lines help you in extracting and installing Nagios plugins:

$ tar zxvf nagios-plugins-2.x.x.tar.gz
$ cd nagios-plugins-2.x.x/
$ ./configure -–with-nagios-user=nagios -–with-nagios- group=nagios
$ make ; sudo make install

After the installation of the core and the plug-in packages, we will be ready to start nagios.

Before starting the Nagios service, make sure that there are no configuration errors by using the following command:

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

Start the nagios service by using the following command:

$ sudo service nagios start
$ sudo chkconfig --–add nagios; sudo chkconfig nagios on

There are many configuration files in Nagios, but the major ones are located under the /usr/local/nagios/etc directory:

The other configuration files under the /usr/local/nagios/etc/objects directory are described as follows:

The nagios.conf file under /usr/local/nagios/etc/ is the main configuration file with various directives that define what all the files include. For example, cfg_dir=<directory_name>.

Nagios will recursively process all the configuration files in the subdirectories of the directory that you specify with this directive as follows:

cfg_dir=/usr/local/nagios/etc/commands
cfg_dir=/usr/local/nagios/etc/services
cfg_dir=/usr/local/nagios/etc/hosts

The Nagios server can do an active or a passive check. If the Nagios server proactively initiates a check, then it is an active check. Otherwise, it is a passive check.

The following are the steps for setting up monitoring for clients:

define host {

  use linux-server 
  host_name remotehost 
  alias Remote 
  Host address 192.168.0.1 
  contact_groups admins
}
Service definition sample:

define service {

  use generic-service
  service_description Root Partition 
  contact_groups admins 
  check_command check_nrpe!check_disk
}

Communication among NRPE components:

On each of the client hosts, perform the following steps:

After getting a good insight into Nagios, we are ready to understand its deployment in the Hadoop clusters.

The second tool that we will look into is Ganglia. It is a beautiful tool for aggregating stats and plotting them nicely. Nagios gives the events and alerts, Ganglia aggregates and presents them in a meaningful way. What if you want to look for the total CPU, memory per cluster of 2000 nodes or total free disk space on 1000 nodes? Plotting the CPU memory for one node is easy, but aggregating it for a group on a node requires a tool that can do this.

We will now discuss some components of Ganglia.

Let's begin by setting up Ganglia, and see what the important parameters that need to be taken care of are. Ganglia can be downloaded from http://ganglia.sourceforge.net/. Perform the following steps to install Ganglia: