I've involved in a cloud development project. I use Nagios core for monitoring servers and devices in this project. As we know, Nagios is one of famous open sourced monitoring tools. I needed references in dealing with Nagios. While I was reading this, it remind me of basic concept of Nagios again.
There are some sections in every chapter. "How to do it" , "How it works" and "There's more". it describes how we start a certain feature of Nagios according to the section in "How to do it" and then explains its mechanism with easy way
in "How it works" and finally there is additional contents related to the chapter in "There's more"
There is impressive paragraph in the book that nagios is close to MONITORING FRAMWORK rather than monitoring tool. It is perfect that describes nagios characteristic because it has already provide ecosystem, for example, lots of plugins support . And it is important to know where to find if need specific plugin that doesn't meet requirements. Author instructed that how to find a plugin that the administrator needs and where.
People who are unfamiliar with Nagios, in my opinion, they may be confused that Nagios has SOFT and HARD state in response to server or host failing. In chapter 3, author tries to explain the difference between two by giving an understandable example.
At last, in chapter 11, he gives an explanation about add-on projects like NRPE, NSClient++, NDOUtils and SNMP trap. If you need to extend the feature of Nagios to provide better-fitting solution on your own production, this will very helpful to you.
Book link: http://www.packtpub.com/nagios-core-administration-cookbook/book