ProxmoxVE instance fails to boot if no config drive is configured

[tormath1]

Bug

If an instance tries to boot on ProxmoxVE without configdrive afterburn will fail to execute correctly and if used for setting hostname the instance will land into emergency shell: https://github.com/coreos/afterburn/blob/main/dracut/30afterburn/afterburn-hostname.service#L31

Operating System Version

Flatcar

Afterburn Version

Latest (5.7.0)

Environment

What hardware/cloud provider/hypervisor is being used to run Afterburn? ProxmoxVE

Expected Behavior

If the config drive does not exist, just exits without error.

Actual Behavior

Emergency shell, the instance does not boot.

Reproduction Steps

1. Boot the instance on ProxmoxVE without config drive

Other Information

• This has been reported here: Proxmox testing with community flatcar/Flatcar#1573 (comment)
• I tried to implement a patch but from what I see, Afterburn does not really allow to exit on error like:

if not config drive:
  exit(0)

[   62.633185] localhost coreos-metadata[704]: Error: failed to run
[   62.633185] localhost coreos-metadata[704]: Caused by:
[   62.633185] localhost coreos-metadata[704]:     0: fetching metadata from provider
[   62.633185] localhost coreos-metadata[704]:     1: maximum number of retries (3) reached
[   62.633185] localhost coreos-metadata[704]:     2: failed to mount (read-only) source '/dev/disk/by-label/cidata' to target '/tmp/afterburn-Kk3KoQ', with type 'iso9660'
[   62.633185] localhost coreos-metadata[704]:     3: ENOENT: No such file or directory
[   62.691725] localhost coreos-metadata[705]: Error: failed to run
[   62.691725] localhost coreos-metadata[705]: Caused by:
[   62.691725] localhost coreos-metadata[705]:     0: fetching metadata from provider
[   62.691725] localhost coreos-metadata[705]:     1: maximum number of retries (3) reached
[   62.691725] localhost coreos-metadata[705]:     2: failed to mount (read-only) source '/dev/disk/by-label/cidata' to target '/tmp/afterburn-2FVY0i', with type 'iso9660'
[   62.691725] localhost coreos-metadata[705]:     3: ENOENT: No such file or directory
[   62.749605] localhost systemd[1]: Dependency failed for initrd.target - Initrd Default Target.
[   62.757531] localhost systemd[1]: initrd.target: Job initrd.target/start failed with result 'dependency'.
[   62.786512] localhost systemd[1]: initrd.target: Triggering OnFailure= dependencies.
[   62.792755] localhost systemd[1]: flatcar-metadata-hostname.service: Main process exited, code=exited, status=1/FAILURE
[   62.799649] localhost systemd[1]: flatcar-metadata-hostname.service: Failed with result 'exit-code'.