Added: support for multiple network interfaces in openstack datasource

[mklejn-ovh]

Proposed Commit Message

fix(openstack): Support mixed dhcp and no-dhcp interfaces

DS OpenstackLocal was only using fallback_interface for it's metadata service detection
which may fail when multiple interfaces, including ones without dhcp, are provided.
Behaviour fixed via iterating over all interfaces until we hit one that has dhcp enabled,
or we fail to find one and explicitly explain that no interface was able to get dhcp lease.

Fixes GH-6786

Additional Context

Right here: GH-6786

Test Steps

Right here: GH-6786

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>)

[blackboxsw]

Basic approach looks good here thanks @mklejn-ovh. I realize that enumerating and walking through multiple interfaces with DHCP requests may lead to delays on BIG systems with multiple NICs if the primary NIC doesn't have DHCP on the attached network.

I think this approach for NIC discovery is ok as you mentioned that NIC attach ordering to VMs is what matters here. Since cloud-init generally prefers that a platform have its primary NIC connected to the platform with access to the instance metadata service (and DHCP), any configuration which diverges from that expectation will either hit 'no IMDS connectivity' issues as you are trying to fix here, or slight delays trying to process non-primary NICs first before finding the right one.

Let's also add a small doc update about multi-NIC discovery in doc/rtd/reference/datasources/openstack.rst.

[blackboxsw]

This approach aligns with what we have currently in GCE datasource with two things missing:

I think we want to distinguish NoDHCPLeaseError condition by logging "Unable to obtain a DHCP lease for "

[blackboxsw]

Generally there is not a lot of value in logging the related traceback via util.logexc if we can valid it. Our common logging pattern gives is the module cloud-init is logging from, so the additional traceback info is nothing more than a lot of noise in our already busy logs. Since you are touching this area. Maybe we make an effort to LOG.debug("OpenStack metadata error: %s") vs "Unable to obtain DHCP lease on %s" etc.

[blackboxsw]

Suggested change

	"All interfaces failed to get dhcp lease"
	"All interfaces failed to get DHCP lease. "

[blackboxsw]

Suggested change

	"Metadata service will NOT be called"
	" OpenStack metadata service will NOT be called"

[blackboxsw]

I wonder if we want to promote this logic into net.find_candidate_nics directly. I see Vultr also attempts to ignore this iface name and I think it's generally irrelevant as a candidate.

[blackboxsw]

Since you are touching functions, please add type hints to function params and expected return values to aid in mypy verification.

[blackboxsw]

Please add typing hints for function returns and params to aid our mypy CI validation.