Check in README.
Stock Ubuntu netboot image.
From http://archive.ubuntu.com/ubuntu/dists/trusty-updates/main/installer-amd64/current/images/netboot/
Stock Ubuntu pre-seed file.
From https://help.ubuntu.com/lts/installation-guide/example-preseed.txt
Slim down Ubuntu netboot file structure. Use Syslinux 4.05's menu.c32 instead of vesamenu.c32.
Create net-console preseed file and pxe conf file.