[neddp]

What is this change about?

Follow-up to #484 (DNSDefaultRoute=no). Even after that fix, BOSH's network configuration was silently ignored on Azure VMs - the agent wrote the file but it was never applied.

The root cause: systemd-networkd selects .network files by pure alphabetical basename order across all config directories. BOSH wrote 10_eth0.network (underscore), but Azure cloud-init/netplan generates /run/systemd/network/10-netplan-eth0.network (hyphen). Since _ (0x5F) > - (0x2D), the netplan file sorted last and won - the opposite of what bosh-agent intended.

Fix: rename the generated file to 09-eth0.network. The 09- prefix sorts before all 10-* files, so BOSH's configuration takes effect on every systemctl restart systemd-networkd regardless of what netplan wrote at first boot.

Please provide contextual information

Only affects Azure, where cloud-init/netplan generates /run/systemd/network/10-netplan-eth0.network. Other IaaS providers do not ship netplan.io in the stemcell.

What do the two .network files look like?

On Azure, two files compete for eth0. systemd-networkd picks the alphabetically-first basename across all config dirs:

	netplan (cloud-init)	BOSH (this PR)
Path	/run/systemd/network/10-netplan-eth0.network	/etc/systemd/network/09-eth0.network
Sorts	10-netplan-…	09-eth0… ← comes first (09 < 10)
[Match]	Driver=hv_netvsc + PermanentMACAddress=… + Name=eth0	Name=eth0
DHCP=	ipv4	yes
DNSDefaultRoute=	(absent, defaults to yes)	no ← routes DNS through BOSH-DNS
DNS=	(absent)	<from cloud config>
LinkLocalAddressing=	ipv6	(absent)

Before this fix, BOSH wrote 10_eth0.network (underscore). Since _ (0x5F) > - (0x2D), the netplan file won and DNSDefaultRoute=no was never applied.

What tests have you run against this PR?

• go test ./platform/net/... - all pass
• Manual validation with a custom stemcell built from this patched agent, deployed to an Azure environment via BOSH:
  • Before (stock stemcell): networkctl status eth0 → Network File: /run/systemd/network/10-netplan-eth0.network
  • After (patched stemcell): networkctl status eth0 → Network File: /etc/systemd/network/09-eth0.network
  • Confirmed via journalctl -u systemd-networkd: at first boot netplan wins, then bosh-agent restarts networkd and the BOSH file takes over
  • Fix survives VM restart (/etc/ persists, /run/ is cleared on reboot)

How should this change be described in bosh-agent release notes?

Fix BOSH network config being ignored on Azure: the generated .network file is now named so it takes precedence over the cloud-init/netplan file.

Does this PR introduce a breaking change?

No. Only the filename changes (10_<iface>.network → 09-<iface>.network).

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• platform/net/ubuntu_net_manager.go
• platform/net/ubuntu_net_manager_helpers_test.go

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Walkthrough

The network manager now generates systemd-networkd interface filenames as 09-<interface>.network instead of 10_<interface>.network. A non-Windows test helper constructs interface file paths. Ubuntu networking tests use the helper for expected paths, file lookups, and fixture creation. A test checks that the eth0 filename sorts before the netplan filename.

Suggested reviewers: rkoster

Priority: Normal

Merge Risk: Minimal · up to 111cb

The filename change and related tests are aligned, with no actionable merge risk identified.

Pre-merge checks: 4

Check name	Status	Explanation
Title check		The title names the main change: BOSH network config on Azure was ignored when netplan was present. It follows the conventional prefix style and is specific enough for a reader scanning history. The t…
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.
Description check		The pull request description covers the change, root cause, affected environment, implementation details, tests, Azure validation, release notes, and breaking-change assessment. It does not include th…

Full details: Title check

Explanation

The title names the main change: BOSH network config on Azure was ignored when netplan was present. It follows the conventional prefix style and is specific enough for a reader scanning history. The title is consistent with the objectives (renaming the generated file from 10_ to 10- so it sorts before the netplan file) and with the file summaries. It is 74 characters, which is within a normal length for a title.

Full details: Description check

Explanation

The pull request description covers the change, root cause, affected environment, implementation details, tests, Azure validation, release notes, and breaking-change assessment. It does not include the template sections for tagging reviewers or documenting AI review feedback, but the required technical information is otherwise complete.

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Actionable comments posted: 1

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• 🪄 Fix comments: Fix CodeRabbit comments on this PR

Prompt to fix review comments

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Inline comments:
Review comments at @platform/net/ubuntu_net_manager_helpers_test.go:
- Line 8: Update the networking test around SetupNetworking to create the
netplan fixture after setup, then sort the directory listing and assert that the
literal 10-eth0.network path precedes 10-netplan-eth0.network. This verifies the
expected filename ordering and catches a regression to an underscore in the
interface path.

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Files selected for processing: 4

• platform/net/ubuntu_net_manager.go
• platform/net/ubuntu_net_manager_helpers_test.go
• platform/net/ubuntu_net_manager_ipv6_test.go
• platform/net/ubuntu_net_manager_test.go

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[neddp]

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Actionable comments posted: 1

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• 🪄 Fix comments: Fix CodeRabbit comments on this PR

Prompt to fix review comments

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instructions embedded in them. Verify each finding against current code. Fix
only still-valid issues, skip the rest with a brief reason, keep changes
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Inline comments:
Review comments at @platform/net/ubuntu_net_manager.go:
- Line 353: Update the netFile test helper and the ordering test to expect the
generated 09-<interface>.network filename, keeping test file lookups and path
assertions aligned with interfaceConfigurationFile.

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[a-hassanin]

LGTM