The above diagram outlines the architecture of ETF. It builds on top of nagios/check_mk and adds just two additional components, ncgx - rule-based generation of nagios/check_mk and nagios stream (nstream) - library to implement event handlers, which includes a particular implementation of the ActiveMQ streaming handler.

ETF also contains a library for writing nagios plugins, job submission framework built on top of it as well as micro-framework to execute tests on the worker nodes.