feat(opennebula): support global SEARCH_DOMAIN for all interfaces

[mcanevet]

Proposed Commit Message

feat(opennebula): support global SEARCH_DOMAIN for all interfaces

netbox-network-config sets a global SEARCH_DOMAIN context variable
(never per-interface ETHx_SEARCH_DOMAIN). The existing get_nameservers()
already handled the global DNS key but silently ignored SEARCH_DOMAIN,
leaving VMs with no DNS search domain configured.

Extend get_nameservers() to append entries from the global SEARCH_DOMAIN
key, matching the existing pattern for global DNS. Per-interface
ETHx_SEARCH_DOMAIN entries take precedence and duplicates are suppressed.

Additional Context

Part of a series bringing cloud-init's OpenNebula datasource to feature
parity with the context-linux package from one-apps.

The global DNS key was already handled by get_nameservers() (line 179
of DataSourceOpenNebula.py). SEARCH_DOMAIN is its natural counterpart
and follows the exact same pattern.

Test Steps

In an OpenNebula VM context, set:

SEARCH_DOMAIN="example.com example.org"

After boot, verify /etc/resolv.conf (or systemd-resolved config) contains
search example.com example.org.

Also verify that setting both ETH0_SEARCH_DOMAIN="iface.example.com" and
SEARCH_DOMAIN="global.example.com" results in both domains present without
duplication.

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>)

[github-actions]

Hello! Thank you for this proposed change to cloud-init. This pull request is now marked as stale as it has not seen any activity in 14 days. If no activity occurs within the next 7 days, this pull request will automatically close.

If you are waiting for code review and you are seeing this message, apologies! Please reply, tagging blackboxsw, and he will ensure that someone takes a look soon.

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[mcanevet]

@blackboxsw rebased

[Copilot]

Pull request overview

This PR updates the OpenNebula datasource’s network-config generation to honor a global SEARCH_DOMAIN context key (in addition to the existing per-interface ETHx_SEARCH_DOMAIN), ensuring DNS search domains are configured even when only the global key is provided.

Changes:

• Extend OpenNebulaNetwork.get_nameservers() to merge global SEARCH_DOMAIN into per-interface search domains while suppressing duplicates.
• Add unit tests covering global-only, merged per-interface + global, and multi-NIC propagation behavior.
• Document SEARCH_DOMAIN as a supported OpenNebula context variable and describe merge precedence.

Reviewed changes

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

File	Description
cloudinit/sources/DataSourceOpenNebula.py	Merge global SEARCH_DOMAIN into the generated netplan nameservers.search list with de-duplication vs per-interface values.
tests/unittests/sources/test_opennebula.py	Add targeted tests for global SEARCH_DOMAIN behavior in get_nameservers() and gen_conf().
doc/rtd/reference/datasources/opennebula.rst	Document SEARCH_DOMAIN and describe how global/per-interface DNS-related keys interact.

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