With my test, Fedora CoreOS need more than 4 GiB of RAM when boot with iPXE.
I could understand why Fedora need a lot of RAM to boot, but why CoreOS need even more RAM than Fedora?
I don’t understand this requirement either. I have an older piece of hardware that I wanted to try with CoreOS but with 2G RAM - you can’t. Since then I have run Fedora Server and now Silverblue on it - it’s tight, but works and runs the minimal apps and containers I am testing.
This is currently under investigation in investigate why we need > 2G memory for live ISO/PXE boot · Issue #407 · coreos/fedora-coreos-tracker · GitHub. The docs currently recommend at least 3GiB of RAM.
I had missed that the recommended memory min requirement has dropped from 4 to 3G. When I tried a bare-metal install (some months ago) the installer process blocked the installation, even when I suspected it would work - which was frustrating. From the bug #407 discussion it seems that this hard requirement can be side-stepped - for those that choose to live dangerously - which seems like a good approach.
You should be able to get by with 2G of memory if you use the coreos.live.rootfs_url= option. I just tried it and it worked. See investigate why we need > 2G memory for live ISO/PXE boot · Issue #407 · coreos/fedora-coreos-tracker · GitHub