Congratulations on your choice of using Nagios Fusion - a powerful application used for connecting your Nagios IT infrastructure monitoring components into a central interface.
This guide is intended to be used by developers who wish to extend the power of Nagios Fusion! Things have changed quite a bit since previous releases. We'll be covering how to build a dashlets and components, along with some of the specific functions you can use while doing so.
Nagios Fusion 4 introduces an entirely new Dashlet system. They've been redesigned to be even easier to work with and develop! Not only that, but the component system has gotten quite a bit of love as well. Just like in Nagios XI, dashlets and components are uploaded as zip files in the manage dashlet/component pages in the Administration pages. The specific syntax for each hasn't changed very much, but the options that you supply to them certainly has. Because of this - all of your old Fusion dashlets and components won't work with Fusion 4.
As a matter of fact: Fusion was built utilizing the component system. When you install Fusion 4 (or upgrade), there are a few components installed by default. One of these is the fusioncore component. Just to give you an idea of the power behind the new system: the fusioncore component - upon successful loading (everytime the Fusion codebase is instantiated) - will register a few callbacks and poll_callbacks. It's these callbacks and poll_callbacks that allow for the automatic logins and every single data point pulled from your Nagios Core and XI servers to work properly!
Don't worry, if you're excited to learn about the callbacks and poll_callbacks, we'll be getting to those pretty soon.