Hello,
I’m the author of the above project. You’ll want to network boot your Pi by setting up a DHCP and TFTP server along with the firmware necessary to boot the Pi, as well as the kernel to run balenaOS. The netboot provisioner project can serve as a reference, but you’ll need to customize this to work as you wish. For reference, here’s the official documentation from the Pi Foundation about how to network boot the Pi: Raspberry Pi Documentation - Raspberry Pi hardware
After the kernel is loading over the network, you’ll want to mount your root filesystem over NBD or NFS. Previously, I’ve chosen NBD, and I have an example prepared you can use as a reference: initramfs-toolkit/run.sh at master · balena-io-experimental/initramfs-toolkit · GitHub
This script will add a hook to the initramfs to setup the network block device (NBD) and tunnel I/O requests over the network. You’ll want to configure your bootloader to load the supplemental initramfs containing the supporting files and configuration for network booting.
Let me know if you have any more questions.