Boot URL:
http://boot.ipxe.org/demo/boot.php
Tutorial:
http://www.rmprepusb.com/tutorials/ipxe
Script:
http://ipxe.org/scripting
Create bootable iPXE images with automated scripts:
https://www.rom-o-matic.eu/
Example:
https://gist.github.com/robinsmidsrod/2234639