...
$ cat preseed_ubuntu/isolinux/isolinux.cfg
default install
label install
menu label ^Install Ubuntu Server
kernel /install/vmlinuz
append debian-installer/locale=en_US console-setup/ask_detect=false keyboard-configuration/layoutcode=us file=/cdrom/preseed/ubuntu-server.seed vga=788 initrd=/install/initrd.gz quiet ---
As the infra-local-controller is supposed not having Internet access, we have to prepare everything into the ISO.