Fix Flaky Test SpecificClusterManagerNodesIT.testElectOnlyBetweenClusterManagerNodes

[kkewwei]

Description

The case is as follows:

1. When the node_t1 is excluded from the vote config, and the cluster starts a new leader election, but the the node node_t2 hasn't been elected as the new leader.

2. At the moment, we send request to get the ClusterManager, we first get ClusterManager name, and leads to the NullPointerException.

internalCluster().nonClusterManagerClient()-> ......->getClusterManagerName()

OpenSearch/test/framework/src/main/java/org/opensearch/test/InternalTestCluster.java

Line 2171 in f0ea056

return client.admin().cluster().prepareState().get().getState().nodes().getClusterManagerNode().getName();

Related Issues

Resolves #16015

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

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[github-actions]

❕ Gradle check result for 1b3920b: UNSTABLE

• TEST FAILURES:

      1 org.opensearch.cluster.MinimumClusterManagerNodesIT.testThreeNodesNoClusterManagerBlock

Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[msfroh]

Checking the history of this test, has this been flaky for more than a year?

The only code related to cluster manager election that I've been able to find changed more recently than ~5 years ago (besides renaming) is the introduction of DecommisionService in 2023.

[kkewwei]

Checking the history of this test, has this been flaky for more than a year?

The only code related to cluster manager election that I've been able to find changed more recently than ~5 years ago (besides renaming) is the introduction of DecommisionService in 2023.

@msfroh I'm not clearly why it wasn’t reported before, maybe the frequency of occurrence is very low and we ignored it? This issue #15944 collects some of the recent case.

Logically speaking, when the cluster has no cluster manager, It's right to return null from getClusterManagerNode, which will hit the case.

[github-actions]

✅ Gradle check result for 4d812e9: SUCCESS

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.98%. Comparing base (036f6bc) to head (4d812e9).

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #16021      +/-   ##
============================================
+ Coverage     71.92%   71.98%   +0.06%     
  Complexity    64400    64400              
============================================
  Files          5281     5281              
  Lines        300995   300995              
  Branches      43479    43479              
============================================
+ Hits         216491   216672     +181     
+ Misses        66793    66569     -224     
- Partials      17711    17754      +43     

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