fix: prevent traceback in util.get_hostname_fqdn when hostname is numeric

[nabil-rady]

Proposed Commit Message

fix: prevent traceback in util.get_hostname_fqdn when hostname is numeric

Catch the AttributeError thrown in util.get_hostname_fqdn and return empty hostname and fqdn to prevent cloud-init from crashing due to bad schema and log a warning instead.

Fixes GH-7006

Additional Context

Reproduced the error using QEMU and the following user-data file

#cloud-config
hostname: 123456
password: password
chpasswd:
  expire: False

Fixes #7007

Test Steps

tox -e py3

Merge type

• Squash merge using "Proposed Commit Message"
• Rebase and merge unique commits. Requires commit messages per-commit each referencing the pull request number (#<PR_NUM>)

[holmanb]

This seems like a weird place to address the error. The schema defines this key as a string - how did it get interpreted as an integer in the first place?

I'm concerned that by trying to fix it here it misses bugs in other parts of the code.

[nabil-rady]

I looked at this discussion, the fqdn fix makes sense and it has context to it, unlike this fix; as quoting the hostname fixes the issue. Would you suggest ignoring this issue or maybe moving the _maybe_set_hostname to the try/except block ?

[holmanb]

It would be better if cloud-init produced an error log rather than a traceback, but this is the expected behavior: if you pass an integer, cloud-init just doesn't know what to do with it. The cloud-init schema command shows that this configuration isn't valid.

[nabil-rady]

@holmanb returned empty hostname and fqdn when hostname is numeric. Running cloud-init status --long produced these warnings.

I am concerned whether we should fallback to cloud in case of a numeric hostname or not.

WARNING:
	- cloud-config failed schema validation! You may run 'sudo cloud-init schema --system' to check the details.
	- Invalid hostname type: expected string, got int
	- Failed to non-persistently adjust the system hostname to 
	- Invalid hostname type: expected string, got int
	- cloud-config failed schema validation! You may run 'sudo cloud-init schema --system' to check the details.
	- Invalid hostname type: expected string, got int
	- Failed to non-persistently adjust the system hostname to 
	- Invalid hostname type: expected string, got int
	- cloud-config failed schema validation! You may run 'sudo cloud-init schema --system' to check the details.
	- Invalid hostname type: expected string, got int
	- Failed to non-persistently adjust the system hostname to 
	- Invalid hostname type: expected string, got int
	- cloud-config failed schema validation! You may run 'sudo cloud-init schema --system' to check the details.
	- Invalid hostname type: expected string, got int
	- Failed to non-persistently adjust the system hostname to 
	- Invalid hostname type: expected string, got int