Do not update unmodifiable fields for StatefulSet

[jiangpengcheng]

(If this PR fixes a github issue, please add Fixes #<xyz>.)

Fixes #638

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Master Issue: #

Motivation

StatefulSet.spec only allow to update below fields:

• replicas
• template
• updateStrategy
• persistentVolumeClaimRetentionPolicy
• minReadySeconds

while during version upgrade of FM, Selector field is changed even with same yaml, and other fields maybe changed in further development too, such as:

• PodManagementPolicy
• ServiceName
• VolumeClaimTemplates

we need to ensure these changed won't update old existing statefulset

Modifications

Do not update unmodifiable fields for StatefulSet

Verifying this change

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This change is a trivial rework / code cleanup without any test coverage.

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This change is already covered by existing tests, such as (please describe tests).

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This change added tests and can be verified as follows:

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• Added integration tests for end-to-end deployment with large payloads (10MB)
• Extended integration test for recovery after broker failure

Documentation

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