The last chapter talked about the extension of Nagios using multiple approaches, including writing your own plugins or commands to send notifications, and performing passive checks and sending the results to Nagios.
Nagios 4 provides a new interface called query handler, which is a general purpose mechanism that allows other processes to communicate with Nagios. It allows two-way communication, so it is possible to both send commands to the Nagios, similar to external commands pipe, and to receive information—either answers to a command that was previously sent to the query handler or asynchronous notifications, such as information about changes in the host and/or service status.
In this chapter, we will cover the following topics:
Understanding the query handler
Learning the services currently available in the query handler
Communicating with various services
Using the Nagios Event Radio Dispatcher (NERD) service to receive real-time notifications about changes...