vmdistributed: change default write requests load balancing policy from first_available to least_loaded

[AndrewChubatiuk]

Summary by cubic

Switches the default load balancing policy for write requests in vmdistributed from first_available to least_loaded to spread write load evenly across VMAgents. Read requests remain on first_available.

• Bug Fixes
  • Update vmauth "write" target to use least_loaded; retry codes unchanged.
  • Adjust tests to expect the new default and add explicit policies for write/read.
  • Add changelog entry.

^{Written for commit 6a9d422. Summary will update on new commits.}

[cubic-dev-ai]

1 issue found across 3 files

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="docs/CHANGELOG.md">

<violation number="1" location="docs/CHANGELOG.md:19">
P2: Custom agent: **Changelog Review Agent**

New changelog entry is missing required issue/PR reference links mandated by the changelog format.</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review, or fix all with cubic.}

[cubic-dev-ai]

P2: Custom agent: Changelog Review Agent

New changelog entry is missing required issue/PR reference links mandated by the changelog format.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At docs/CHANGELOG.md, line 19:

<comment>New changelog entry is missing required issue/PR reference links mandated by the changelog format.</comment>

<file context>
@@ -16,6 +16,7 @@ aliases:
 * FEATURE: [vmauth](https://docs.victoriametrics.com/operator/resources/vmauth): previously VMAuth could read configuration only from predefined locations; now VMAuth supports arbitrary filesystem access configuration, allowing users to reference required files directly and reducing configuration workarounds. See [#899](https://github.com/VictoriaMetrics/operator/issues/899).
 
 * BUGFIX: [converter](https://docs.victoriametrics.com/operator/integrations/prometheus/#objects-conversion): disable all prometheus controllers if CRD group was not found. See [#2838](https://github.com/VictoriaMetrics/helm-charts/issues/2838).
+* BUGFIX: [vmdistributed](https://docs.victoriametrics.com/operator/resources/vmdistributed/): change default load balancing policy for write requests from `first_available` to `least_loaded`. This should allow to evenly distribute write load across all VMAgents.
 
 ## [v0.69.0](https://github.com/VictoriaMetrics/operator/releases/tag/v0.69.0)
</file context>

[vrutkovs]

I think it needs to be complimented with removing exclude IDs from vmAgentTargetRef, so that we'd be writing in all zones (queues would grow when its being updated)

[AndrewChubatiuk]

vmagent is excluded as well in case if it can be restarted due to upgrade

[vrutkovs]

Thanks, could you backport it to 0.68.x too please?