[RFE] Flatcar boot partition size shrink effort

[ader1990]

Current situation

Currently, the Flatcar boot partition is set to 128 MB. There was a slow increase over the years of the Linux kernel, dracut and systemd binaries or other required packages in the initrd. The current usage in the latest Alpha is of around 62MB, which is critically close to the half of the size.

From my limited understanding, if we pass the 64MB mark, there will be issues, as the kernel should fit twice for the A/B update to work.

Impact

Doubling the boot partition will limit the old clients to update. Maybe there are other implications, feel free to update the list.

Ideal future situation

Without increasing the boot partition, I see no way for the medium to long term to implement in an upstream clean way things like systemd upgrades, linux kernel upgrades or security features like LUKS encryption/decryption, HSM integration.

Additional comments

For example, the current upgrade to systemd 255 is blocked by this issue and the only way forward is to axe the kbd upstream package contents with the minimal necessary files. The problem is that if we implement such a hack, there are going to be unforseen issues in the future if a user wants to use the upstream kbd package features that we are removing. This solution will bring technical debt in the future, as the initrd required packages need to go through the same process. https://github.com/flatcar/scripts/pull/1679

The PR to add TPM/TANG support might be blocked too for the same reason: https://github.com/flatcar/scripts/pull/1560.

If in the future, if we want to add LUKS2 support with HSM, there might be again, the same blocker.