Nagios Core, the open source version of the Nagios monitoring framework, is an industry standard for network monitoring hosted on Unix-like systems, such as GNU/Linux or BSD. It is very often used by network and system administrators to check the connectivity between hosts and to ensure that network services are running as expected.
Where home-grown scripts performing network checks can rapidly become unmaintainable and difficult for newer administrators to customize safely, Nagios Core provides a rigorous and configurable monitoring framework to make checks in a consistent manner and to alert appropriate people and systems of any problem it detects.
This makes Nagios Core a very general monitoring framework rather than an out-of-the-box monitoring solution, which is known to make it a little unfriendly to beginners and something of a "black box", even to the otherwise experienced administrators. Busy administrators charged with setting up a Nagios Core system will often set it up to send PING requests to a set of hosts every few minutes and send them an e-mail about any problem, and otherwise never touch it. More adventurous administrators new to the system might instate a few HTTP checks to make sure that company websites respond.
Nagios Core is capable of a great deal more than that, and this book's recipes are intended to highlight all of the different means of refining and controlling checks, notifications, and reporting for Nagios Core, rather than being a list of instructions for using specific plugins, of which there are many hundreds available online at the Nagios Exchange at https://exchange.nagios.org/. The book's fundamental aim is to get administrators excited about the possibilities of Nagios Core beyond elementary default checking behavior so that they can use much more of the framework's power and make it into the centerpiece of their network monitoring.
This also includes installing and even writing custom plugins beyond the standard Nagios Plugins set, writing and refining one's own checks, working with the very powerful Simple Network Management Protocol (SNMP), and the recording and reporting of performance data. It also includes refining notification behavior to only send appropriate notifications at appropriate times to appropriate people or systems, basic visualization options, identifying breakages in network paths, clever uses of the default web interface, and even extending Nagios Core with other open source programs. It includes all this in order to virtually check any kind of host property or network service on any network.
Where possible, this book focuses on add-ons written by the Nagios team themselves, particularly NRPE and NSCA. It omits discussion of popular forks of Nagios Core, such as Icinga. In the interest of conferring an in-depth understanding of advanced Nagios Core configuration, it also does not discuss any configuration frontends or wizards, such as NConf. Finally, as a Packt open source series book focusing on the use of the freely available Nagios Core, it also does not directly discuss the use of Nagios XI, the commercial version of the software supported by the Nagios team. This is done to instill a thorough understanding of Nagios Core itself, rather than to reflect the personal opinions of the author; curious administrators should definitely investigate all of these projects.
Chapter 1, Understanding Hosts, Services, and Contacts, gives you a basic idea of hosts, services, and contacts followed by the summary of this chapter.
Chapter 2, Working with Commands and Plugins, explains the architecture of plugins and commands, including installing new plugins and defining custom uses of existing ones. It also walks us through how to write a new plugin with Perl.
Chapter 3, Working with Checks and States, explains how Nagios Core performs its checks and how to customize that behavior, including scheduling downtime for hosts and services and managing "flapping" for hosts or services that keep going up and down.
Chapter 4, Configuring Notifications, explains the logic of how Nagios Core decides on what basis to notify, when, and to whom, including examples of implementing a custom notification method, escalating notifications that aren't fixed after a certain period of time, and scheduling contact rotation.
Chapter 5, Monitoring Methods, gives examples of the usage of some of the standard Nagios Plugins sets, moving from basic network connectivity checks with PING and HTTP to more complex and powerful checks involving SNMP usage.
Chapter 6, Enabling Remote Execution, shows how to use NRPE as a means of working around the problem of not being able to check system properties directly over the network, including a demonstration of the more advanced methods of check_by_ssh and check_mk.
Chapter 7, Using the Web Interface, shows some less-used features of the web interface to actually control how Nagios Core is behaving and to see advanced reports, rather than simply viewing the current state information. Use of the network map is not discussed here but in the next chapter.
Chapter 8, Managing Network Layout, explains how to make Nagios Core aware of the structure and function of your network with a focus on hosts and services depending on one another to function correctly, including monitoring clusters and using that layout information to build a network status map, optionally with icons and a background.
Chapter 9, Managing Configuration, shows how to streamline, refine, and control Nagios Core's configuration at a low level without the use of frontends. It focuses on the clever use of groups, templates, macros, and custom directives, and gives an example of generating configuration programmatically with the templating language m4.
Chapter 10, Security and Performance, shows how to manage simple access control, debugg runtime problems, and keep tabs on how Nagios Core is performing, and also contains a demonstration of basic monitoring redundancy.
Chapter 11, Automating and Extending Nagios Core, explains how to submit check results from other programs (including NSCA) to provide information about external processes via the commands file, and an introduction to a few popular add-ons (NDOUtils, MK Livestatus, NagVis, and Nagiosgraph).
In an attempt to work with a "standard" installation of Nagios Core, this book's recipes assume that Nagios Core 4.0 or later and the Nagios Plugins set have been installed in /usr/local/nagios by the Nagios Quickstart Guides available at https://assets.nagios.com/downloads/nagioscore/docs/nagioscore/4/en/quickstart.html.
If your system's package repositories include a package for Nagios Core 4.0 or later that you would prefer to use, this should still be possible, but the paths of all the files are likely to be very different. This is known to be a particular issue with the nagios3 package on Debian or Ubuntu systems. If you are familiar with the differences in the installation layout that your packaging system imposes, then you should still be able to follow the recipes with only a few path changes.
This book is aimed at system and network administrators who are comfortable with basic Unix-like system administration via the command line. It is best suited for GNU/Linux administrators, but should work fine for BSD administrators too. It has particular focus on the kind of administrator identified in the preface: one who is comfortable working with their Unix-like system, may well have a basic Nagios Core installation ready with some PING checks, and now wants to learn how to use more of the framework's power and understand its configuration in more depth.
Administrators should be comfortable with installing library dependencies for the extensions, plugins, and add-ons discussed in the book. An effort is made to mention any dependencies; however, how these are best installed will depend on the system and its package repository. In almost all cases, this should amount to installing some common libraries and their headers from a packaging system. Debian and Ubuntu package names are given for some more complex cases.
The easier recipes in the first five chapters involve some recap of the basics of configuring Nagios Core objects. Users completely new to Nagios Core who have just installed it will almost certainly want to start with Chapter 1, Understanding Hosts, Services, and Contacts, after completing the Nagios Quickstart Guide, as the latter chapters assume a fair amount of knowledge.
In this book, you will find several headings that appear frequently (Getting ready, How to do it, How it works, There's more, and See also).
To give clear instructions on how to complete a recipe, we use these sections as follows:
This section tells you what to expect in the recipe, and describes how to set up any software or any preliminary settings required for the recipe.
This section usually consists of a detailed explanation of what happened in the previous section.
This section consists of additional information about the recipe in order to make the reader more knowledgeable about the recipe.
In this book, you will find a number of text styles that distinguish between different kinds of information. Here are some examples of these styles and an explanation of their meaning.
Code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, and user input are shown as follows: "Nagios Core will only need whatever information the ping(8) tool would need for its own check_ping command."
A block of code is set as follows:
define service {
use generic-service
host_name sparta.example.net
service_description HTTP
check_command check_http
}When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:
define host {
host_name sparta.example.net
alias sparta
address 192.0.2.21
max_check_attempts 3
check_period 24x7
check_command check-host-alive
contacts nagiosadmin
notification_interval 60
notification_period 24x7
}Any command-line input or output is written as follows:
# cd /usr/local/nagios/etc/objects # vi sparta.example.net.cfg
New terms and important words are shown in bold. Words that you see on the screen, for example, in menus or dialog boxes, appear in the text like this: "If the server restarted successfully, the web interface should show a brand new host in the Hosts list, in the PENDING state as it waits to run a check that the host is alive."
Feedback from our readers is always welcome. Let us know what you think about this book—what you liked or disliked. Reader feedback is important for us as it helps us develop titles that you will really get the most out of.
To send us general feedback, simply e-mail <[email protected]>, and mention the book's title in the subject of your message.
If there is a topic that you have expertise in and you are interested in either writing or contributing to a book, see our author guide at www.packtpub.com/authors.
Now that you are the proud owner of a Packt book, we have a number of things to help you to get the most from your purchase.
You can download the example code files from your account at http://www.packtpub.com for all the Packt Publishing books you have purchased. If you purchased this book elsewhere, you can visit http://www.packtpub.com/support and register to have the files e-mailed directly to you.
Although we have taken every care to ensure the accuracy of our content, mistakes do happen. If you find a mistake in one of our books—maybe a mistake in the text or the code—we would be grateful if you could report this to us. By doing so, you can save other readers from frustration and help us improve subsequent versions of this book. If you find any errata, please report them by visiting http://www.packtpub.com/submit-errata, selecting your book, clicking on the Errata Submission Form link, and entering the details of your errata. Once your errata are verified, your submission will be accepted and the errata will be uploaded to our website or added to any list of existing errata under the Errata section of that title.
To view the previously submitted errata, go to https://www.packtpub.com/books/content/support and enter the name of the book in the search field. The required information will appear under the Errata section.
Piracy of copyrighted material on the Internet is an ongoing problem across all media. At Packt, we take the protection of our copyright and licenses very seriously. If you come across any illegal copies of our works in any form on the Internet, please provide us with the location address or website name immediately so that we can pursue a remedy.
Please contact us at <[email protected]> with a link to the suspected pirated material.
We appreciate your help in protecting our authors and our ability to bring you valuable content.
If you have a problem with any aspect of this book, you can contact us at <[email protected]>, and we will do our best to address the problem.