fix(localdns): wait for resolv.conf update after networkctl reload to prevent race condition#7749
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cameronmeissner merged 14 commits intomainfrom Feb 3, 2026
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Pull request overview
This PR fixes a race condition that occurs after calling networkctl reload to update DNS configuration. Previously, the code would proceed immediately after the reload command without waiting for systemd-resolved to actually update the /run/systemd/resolve/resolv.conf file, potentially causing subsequent operations to work with stale DNS information.
Changes:
- Added
wait_for_dns_config_applied()function that polls resolv.conf to verify DNS configuration changes have been applied - Integrated the wait function after both networkctl reload calls to ensure DNS changes are complete before proceeding
- Added comprehensive test coverage for the new function
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
| parts/linux/cloud-init/artifacts/localdns.sh | Implements the new wait_for_dns_config_applied() function and integrates it after networkctl reload calls in disable_dhcp_use_clusterlistener and cleanup_iptables_and_dns |
| spec/parts/linux/cloud-init/artifacts/localdns_spec.sh | Adds comprehensive test coverage for wait_for_dns_config_applied with tests for success cases, timeout cases, edge cases, and partial IP matching |
saewoni
changed the title
Update log messages to use Error: prefix when wait_for_dns_config_applied fails, since these are failure conditions (return 1), not warnings. Updated corresponding test assertion.
…ad of being interpreted as regex wildcards
yewmsft
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yewmsft
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…conf after shutdown
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… prevent race condition (#7749) Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com> Signed-off-by: Devin Wong <wongsiosun@outlook.com>
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… prevent race condition (#7749) Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
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What this PR does / why we need it:
Immediately after networkctl reload, DNS settings may not have propagated from systemd-networkd (via DHCP) to systemd-resolved yet. As a result, /run/systemd/resolve/resolv.conf can still reflect the previous upstream DNS servers when replace_azurednsip_in_corefile runs.
This happens because networkctl reload only triggers a reload request over D-Bus; it does not wait for systemd-networkd to finish reprocessing configuration, re-acquire DHCP leases, or update systemd-resolved.
Which issue(s) this PR fixes:
Fixes #
to test: shellspec --shell bash --format d spec/parts/linux/cloud-init/artifacts/localdns_spec.sh
copied the script to the localdns-enabled node with replacing systemd-notify WATCHDOG=1 with echo systemd-notify WATCHDOG=1 to have the watchdog restart localdns (simulating what cx had before their race condition problem). I have 2 custom vnet dns servers
updated.localdns.corefile has the correct custom vnet dns servers.