== Don't use the python tftpd
As of 2.4.x, cobbler doesn't properly manage symlinks if you want to use the python in.tftpd. According to cobbler/cobbler#1150 this doesn't look like it'll be fixed until the 3.0 timeframe?
== Repos
The list of apt components that each repo needs to have in orderto boot off of a local mirror are at least:
main universe restricted main/debian-installer restricted/debian-installer
So at /cobbler_web/repo/edit/, click on the advanced tab, and make sure that apt components are listed there.
The dist names only need to be , -updates, -security (e.g. "trusty trusty-updates trusty-security")