This has worked in the past (at least on MAAS 2.2) if the BIOS is using ‘iBFT’ (which is almost certainly is). In order to make it work, you need to add ‘iscsi_auto’ to the global kernel parameters in MAAS which instructs the initramfs to look for the iBFT information and make use of it.
In iBFT mode, the network card runs a boot service that provides BIOS level and very slow access to the disk via the NIC in order to allow the boot loader to get it’s necessary files. Once the OS boots it takes over with it’s own network connection which works at full speed. To make this work, the iBFT table is populated with the IP address and iSCSI target/IP/credentials which is used by the OS.
I had to make a patch to open-iscsi to make this work for another MAAS user in the past, the patch was that cloud-init bugged out in the presence of an iBFT booted environment due to an unexpected value in the file that describes how the network was configured by the kernel during early boot when it takes over the IP that was previously used by the boot loader. That bug was https://bugs.launchpad.net/ubuntu/+source/open-iscsi/+bug/1684039. That bug also has details on how to simulate an iBFT environment using qemu in case anyone wants to test without a real such server.
However, iBFT support is not a tested or officially supported. Part of the reason it works is that until MAAS 2.3, MAAS used iSCSI to boot the ephemeral images for commissioning/deployment - thus open-iscsi was installed in those environments and supported the iscsi_auto flag (if the open-iscsi package isn’t installed when the initramfs used to boot these environments is generated, the relevant scripts will not exist to handle iBFT boot). MAAS 2.3 moved away from using iSCSI for that and it’s possible support for this might ‘accidentally’ break by having open-iscsi removed from the ephemeral images. As of right now, the images still have open-iscsi installed and I have no idea if this will change, I just generally note the disclaimer that it MAY change in the future. However, any installed machines would continue to work, the risk is that you would no longer be able to deploy new machines.
I would also note that iBFT is explicitly NOT supported by the normal Ubuntu Installer (any of the 3 versions of it) right now, however I know that this issue is also being actively worked though cannot make any promises that support will land. Though it’s mostly irrelevant for MAAS, but I thought I would mention it.