fix(helm): add backstop livenessProbe to DHCP config-sync sidecar

[dmathur0]

Description

Split out of #23 so this low-risk, Helm-only change can ship independently while the KEA bootstrap-drift detection/re-apply application logic in #23 waits for QA.

Adds a conservative backstop livenessProbe to the config-sync-v4 container in deploy/helm/templates/dhcp.yaml. If the in-loop KEA divergence check ever wedges (asyncio loop stalls, or the kea control socket stays unresponsive long enough that get_config() keeps raising), kubelet recycles the sidecar. On restart the container re-runs the unconditional "Run once" set_config() and heals the deadlock — even if the in-loop check itself is broken.

• Probes the healthcheck endpoint (/healthcheck on port 9090) in the same pod/network namespace, matching the pattern used by the kea container's probe.
• Thresholds are deliberately looser than the other probes (failureThreshold * periodSeconds = 300s of failure) so the in-loop recovery (~10s) wins under normal conditions and we only recycle the sidecar when the loop itself is the problem.

This contains no application code — it's purely the Kubernetes safety net, so it carries minimal risk and does not need to wait on QA of the drift-recovery logic.

Validation

• helm template test . --values values-ci.yaml renders cleanly with the new probe on the config-sync container.
• Standard CI passes.
• Kind integration passes, or this PR explains why it was not run.
  https://github.com/NVIDIA/nv-config-manager/actions/runs/28194950934/job/83519142880

Checklist

• I am familiar with the contributing guidelines in CONTRIBUTING.md.
• Commits are signed off for DCO compliance.
• New or existing tests cover these changes, or the PR explains why tests are not needed. (Helm-only probe addition; covered by Kind integration rendering.)
• Documentation is updated for user-facing behavior changes.
• Generated artifacts are updated when applicable.

Summary by CodeRabbit

• Bug Fixes
  • Added an additional health check to improve recovery for DHCP config synchronization.
  • Helps the service restart more reliably if the sync process becomes unresponsive.

[coderabbitai]

📝 Walkthrough

Walkthrough

Adds an HTTP liveness probe to the config-sync-v4 container in the DHCP Helm template, checking /healthcheck on port 9090 with separate timing and failure thresholds.

Changes

DHCP config-sync backstop probe

Layer / File(s)	Summary
config-sync-v4 liveness probe deploy/helm/templates/dhcp.yaml	Adds an HTTP GET livenessProbe for config-sync-v4 against /healthcheck on port 9090 with its own delay, period, timeout, and failure settings.

🎯 2 (Simple) | ⏱️ ~10 minutes

🐰 I hop by the helm, so neat and bright,
/healthcheck now watches through the night.
If config-sync naps, the probe will say “boo,”
then back to startup the pod will chew.
Ears up, wheels turn, the cluster sings too.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and accurately summarizes the main Helm change: adding a backstop liveness probe to the DHCP config-sync sidecar.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch davesh/dhcp-config-sync-liveness-backstop

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