Question regarding physical storage

[peltho]

Hello,
I'm planning to use Flatcar for a cluster of 3 devices.
Only one of the three has physical storage. It would act as the master node.

Each of the two others only have SPI module (16MB) to hold their bootloader.

Is it possible to perform PXE boot for the two workers sharing one NFS storage for their OS + data?

[t-lo]

Yes, that should work, though slightly different from what you are proposing.
The default Flatcar PXE boot set-up (https://www.flatcar.org/docs/latest/installing/bare-metal/booting-with-pxe/) runs entirely from RAM, which is what would work best for your use case. You can update the operating system simply by replacing the PXE boot image on your tftp server with the latest release, and rebooting.

For persistence you would pass an Ignition config via PXE that instructs the worker to mount the NFS export at a desired location, then run your workloads from there, and also use it as persistent storage. A simple example can be found here: https://www.flatcar.org/docs/latest/setup/storage/mounting-storage/#mounting-nfs-exports

[t-lo]

To arrive at a functional configuration I recommend you iterate on a test set-up using qemu in a local VM. Our "getting started" guide has you covered: https://www.flatcar.org/docs/latest/installing/

While there are fundamental differences between in-memory PXE boot and running Flatcar in a local VM, it's likely the fastest way to get to a set-up where Flatcar mounts an NFS export and your workload applications can use it.