Copy the LY2 ONIE installer (Ex: onie-installer-quanta_ly2 for LY2) into the http server using any copy mechanism (tftp, scp, etc.).
If the switch is not pre-installed with ONIE image, download and install the same at the u-boot prompt.
Once the switch is reset with ONIE image (ONIE kernel and u-boot) installed, it tries to locate the installer using discovery methods. Once the installer is located, the switch reboots again and ONIE kernel executes NOS.