feat: support graceful scale-down for AlluxioRuntime using AdvancedStatefulSet

[jakharmonika364]

Ⅰ. Describe what this PR does

This PR implements a graceful decommissioning workflow for Alluxio workers during scale-in. It adds a new AdvancedStatefulSet feature gate that allows Fluid to leverage OpenKruise capabilities for finer pod lifecycle management. When enabled, workers are decommissioned and their cached data is migrated before the pods are terminated, ensuring cluster stability and data availability during scaling operations.

Ⅱ. Does this pull request fix one issue?

fixes #4193

Ⅲ. List the added test cases (unit test/integration test) if any, please explain if no tests are needed.

• pkg/ddc/alluxio/operations/decommission_test.go: Unit tests for Alluxio decommissioning commands and active worker count parsing.
• Integration verified via SyncReplicas logic to ensure scale-down waits for successful decommissioning.

Ⅳ. Describe how to verify it

1. Enable AdvancedStatefulSet=true in the feature gates.
2. Deploy an AlluxioRuntime and scale down the replicas.
3. Verify that the targeted worker pods are decommissioned from the Alluxio master before the StatefulSet actually deletes the pods.

Ⅴ. Special notes for reviews

The feature is currently in Alpha and disabled by default. It provides the necessary infrastructure to support selective pod deletion in later phases.

[fluid-e2e-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[fluid-e2e-bot]

Hi @jakharmonika364. Thanks for your PR.

I'm waiting for a fluid-cloudnative member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[gemini-code-assist]

Code Review

This pull request introduces graceful worker scale-down for Alluxio by decommissioning workers before they are terminated by the StatefulSet controller, ensuring cached blocks can be migrated. This functionality is gated by a new AdvancedStatefulSet feature. The changes include new decommissioning operations in AlluxioFileUtils, integration into the SyncReplicas reconciliation loop, and comprehensive unit tests. Review feedback suggests improving context propagation by replacing context.TODO(), optimizing efficiency by passing existing runtime objects to avoid redundant API lookups, and refining error handling during the draining phase to prevent log noise.

[codecov]

Codecov Report

❌ Patch coverage is 39.80583% with 62 lines in your changes missing coverage. Please review.
✅ Project coverage is 58.11%. Comparing base (82e490e) to head (c62bca3).

Files with missing lines	Patch %	Lines
pkg/ddc/alluxio/replicas.go	11.76%	59 Missing and 1 partial ⚠️
pkg/features/features.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5805      +/-   ##
==========================================
- Coverage   58.17%   58.11%   -0.06%     
==========================================
  Files         478      480       +2     
  Lines       32485    32588     +103     
==========================================
+ Hits        18899    18940      +41     
- Misses      12042    12103      +61     
- Partials     1544     1545       +1     

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[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud