Track Cluster API worker cloud-config stanza coverage

[navaneeth-dev]

Goal

Track the cloud-config surface emitted by Cluster API's kubeadm worker-node template and make support status explicit. Butane Init must reject unsupported stanzas rather than silently discard them.

Authoritative source: Cluster API v1.11.1 worker node template.

Coverage

Cloud-config stanza	Cluster API usage	Status	Expected Butane implementation
write_files	Required for the kubeadm join config, scripts, certificates, and extra files	Unsupported	storage.files
runcmd	Required to run pre-kubeadm commands, kubeadm join, the sentinel command, and post-kubeadm commands	Unsupported	Generated scripts and systemd oneshot units
users	Optional extra worker users	Partial	passwd.users; currently supports name, passwd, gecos, homedir, shell, and ssh_authorized_keys
bootcmd	Optional early boot commands	Unsupported	Generated scripts and systemd oneshot units
ntp	Optional NTP configuration	Unsupported	Flatcar time-sync configuration/files and units
disk_setup	Optional partition-table setup	Unsupported	Butane storage configuration where semantics can be preserved
fs_setup	Optional filesystem setup	Unsupported	Butane storage.filesystems
mounts	Optional mounts	Unsupported	Butane filesystems and/or systemd mount units

Nested users work

• users[].groups and users[].primary_group are tracked in Support Cluster API supplementary and primary groups #4.
• inactive, lock_passwd, and sudo remain unsupported and must continue to fail conversion until separately designed.

Priority

1. Complete users group semantics.
2. Support write_files.
3. Support runcmd sufficiently to boot and join a worker.
4. Prove the minimum worker path with the QEMU CI test tracked in Run Flatcar QEMU provisioning test in CI #5.
5. Add optional bootcmd, ntp, disk_setup, fs_setup, and mounts based on actual Cluster API fixtures.

Completion criteria

• README contains an up-to-date support matrix.
• Each supported stanza has positive, invalid-input, and unsupported-field tests.
• Unsupported stanzas produce explicit path-aware errors.
• The default Cluster API worker cloud-config transpiles without silently changing semantics.

[estherdomfeh213]

Hi, I'd like to help with this. I'm going to start with the README support matrix since it's the first item on the completion list and feels like a good way to get familiar with the project. I'll have a draft PR up soon.

[navaneeth-dev]

Don't start work yet, this is being worked by LFX Mentorship.

After the project is stable you can contribute.

[estherdomfeh213]

Thanks for letting me know, I understand. Good luck with the project! :)