fix (GCE): wait for NIC before fetching metadata

[goldberl]

Proposed Commit Message

fix (GCE): wait for NIC before fetching metadata

On C3-metal GCE instances, cloud-init runs before the network
interface is ready, causing datasource detection to fail and
preventing SSH access.

This change adds a polling loop for metadata fetch that waits
for a usable NIC and metadata service.Fixes boot issues on GCE
instances without breaking existing unit tests.

Fixes GH-6737

Additional Context

• Addresses [bug] DataSourceGCELocal fails on GCE c3-metal instances due to NIC not ready at first boot #6737
• Similar to this PR: fix (EC2): wait for NICs before failing datasource discovery #6698

Test Steps

1. Launch a C3 instance on Google Cloud

gcloud compute instances create goldberl-c3-test-01 \
  --project=ubuntu-os-support \
  --zone=europe-west1-c \
  --machine-type=c3-standard-192-metal \
  --maintenance-policy=TERMINATE \
  --provisioning-model=STANDARD \
  --image=projects/ubuntu-os-support/global/images/melissa-questing-serial-eu \
  --boot-disk-size=10GB \
  --boot-disk-auto-delete

2. Wait several minutes until the machine is ready, then check cloud-init status --long
   You will see something like this:

ubuntu@goldberl-c3-test-01:~$ cloud-init status --long
status: error
extended_status: error - done
boot_status_code: enabled-by-generator
last_update: Thu, 01 Jan 1970 00:00:28 +0000
detail: Cloud-init enabled by systemd cloud-init-generator
errors:
	- No instance datasource found.
	- Can not apply stage config, no datasource found! Likely bad things to come!
	- Can not apply stage final, no datasource found! Likely bad things to come!
recoverable_errors:
WARNING:
	- Getting data from <class 'cloudinit.sources.DataSourceGCE.DataSourceGCELocal'> failed
	- No instance datasource found! Likely bad things to come!
	- required key instance-id returned nothing. not GCE
	- Getting data from <class 'cloudinit.sources.DataSourceGCE.DataSourceGCELocal'> failed
	- Can not apply stage config, no datasource found! Likely bad things to come!
	- Can not apply stage final, no datasource found! Likely bad things to come!

3. Apply this patch to the /usr/lib/python3/dist-packages/cloudinit/sources/DataSourceGCE.py file
4. Clean cloud-init logs with sudo cloud-init clean --logs --config all and then reboot machine
5. SSH into the machine after the reboot, and see the status again

ubuntu@goldberl-c3-test-01:~$ cloud-init status --long
status: done
extended_status: degraded done
boot_status_code: enabled-by-generator
last_update: Thu, 01 Jan 1970 00:00:42 +0000
detail: DataSourceGCELocal
errors: []
recoverable_errors:
WARNING:
	- Publishing host keys failed!
	- Publishing host keys failed!

And you can check the patch was executed via the following commands:

sudo cat /var/log/cloud-init.log | grep "No NICs yet"
sudo cat /var/log/cloud-init.log | grep "Eligible NICs found"

You will see soemthing like this

2026-02-10 21:22:46,296 - DataSourceGCE.py[DEBUG]: No NICs yet, waiting for udev/network...
2026-02-10 21:22:53,098 - DataSourceGCE.py[DEBUG]: Eligible NICs found after 6802 ms: ['enp5s0f0']

The DataSourceGCELocal is properly detected this time.

Although we still see warnings about publishing host keys failing. This may be a different issue.

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>)