fix(cloudstack): get domain name information from network manager leases

[ani-sinha]

This is a series of three independent commits.
The first commit adds helper functions in dhcp module to get dhcp lease information from network manager.
The second commit fixes a mock leak in existing cloudstack unit test code.
The third commit adds ability in cloud stack code trying to get domain name use network manager leases as well (in addition to trying networtkd and isa dhclient as it does today already).

This change has been tested by our (Red Hat) customer. After the change, we see logs of this type:

2026-04-04 15:19:54,813 - DataSourceCloudStack.py[DEBUG]: FQDN requested
2026-04-04 15:19:54,813 - DataSourceCloudStack.py[DEBUG]: Try obtaining domain name from networkd leases
2026-04-04 15:19:54,813 - DataSourceCloudStack.py[DEBUG]: Could not obtain FQDN from networkd leases. Falling back to ISC dhclient
2026-04-04 15:19:54,813 - DataSourceCloudStack.py[DEBUG]: Could not obtain FQDN from ISC dhclient leases. Falling back to Network Manager leases
2026-04-04 15:19:54,814 - subp.py[DEBUG]: Running command ['/usr/bin/nmcli', '-f', 'DHCP4', 'd', 'show'] with allowed return codes [0] (shell=False, capture=True)
2026-04-04 15:19:54,827 - performance.py[DEBUG]: Running ['/usr/bin/nmcli', '-f', 'DHCP4', 'd', 'show'] took 0.014 seconds
2026-04-04 15:19:54,828 - DataSourceCloudStack.py[DEBUG]: Obtained the following FQDN: foo.bar.baz.com
2026-04-04 15:19:54,828 - xxx[DEBUG]: XYZ hostname: foo.bar.baz.com

Proposed Commit Message

Commit 1:

feat(dhcp): Add network manager lease parsing capability

DHCP leases can be directly obtained from network manager through appropriate
command to the network manager cli. Add a couple of helper functions to get
the lease information from network manager.

In a subsequent patch, we will use the helper function from cloud stack
datasource to get the lease information from network manager.

Commit 2:

test: fix test_get_domainname_isc_dhclient mock leak

Without mocking out dhcp.IscDhclient.get_newest_lease_file_from_distro, the
functions on some platforms returns None. This means
get_key_from_latest_lease() bails out early without calling parse_leases()
to parse the lease file. Fix it.

Commit 3:

fix(cloudstack): get domain name information from network manager leases

Red Hat uses network manager as the supported dhcp client. If network manager
cli is available, we should try to get domain name information directly from
the network manager leases before asking distro specific dhcp client
(dhcpcd by default).

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>)

[ani-sinha]

@holmanb @TheRealFalcon please review

[blackboxsw]

Thanks for this proposal @ani-sinha. I think it is almost there, but needs a bit more support awareness of multi-NIC environments with two active interfacees and test coverage in test_dhcp.py.

[Copilot]

Pull request overview

This PR extends CloudStack hostname/FQDN discovery by adding NetworkManager (nmcli) DHCP lease parsing helpers and using them as an additional fallback when determining the DHCP-provided domain name. It also adjusts CloudStack unit tests to avoid a mock leak and to cover the new NetworkManager fallback behavior.

Changes:

• Add nmcli-based DHCP4/DHCP6 lease parsing helpers in cloudinit/net/dhcp.py.
• Update DataSourceCloudStack._get_domainname() to attempt NetworkManager leases after ISC dhclient leases.
• Fix/extend unit tests to properly mock ISC dhclient lease file selection and to validate the NetworkManager path.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
cloudinit/net/dhcp.py	Adds helper functions to run nmcli and parse NetworkManager DHCP lease output.
cloudinit/sources/DataSourceCloudStack.py	Adds a NetworkManager lease fallback when determining domain name for FQDN construction.
tests/unittests/sources/test_cloudstack.py	Updates mocks to avoid platform-dependent behavior and adds a test for the NetworkManager fallback path.

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