Current situation

Systemd-sysext images have a compatibility matching mechanism that searches for the matching OS version or custom sysext level setting. On Flatcar there is just the OS version set in /etc/os-release until now.

Impact

Sysext images can't easily be used together with autoupdates that change the OS version.

Ideal future situation

We define a Flatcar sysext level like 1.0 which the sysext images can match for instead of the OS version.
Since there is not backwards compatibility mechanism in the matching, e.g., to specify a minimum version, the long term plan for this setting is a bit unclear and we should work with upstream to get a more flexible mechanism. Also, matching for the architecture should be added.

Implementation options

1.0 (or actually 1.0-amd64 and 1.0-arm64 to forbid mixing architectures but I think we can address this upstream in parallel and start without baking it in)

Additional information