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This is a mini-KIP proposal to allow a legacy Kafka in the 3.9.2 maintenance release to invoke an AlterConfigPolicy
in the same way when running in ZooKeeper mode and KRaft mode, thereby facilitating migration to KRaft.

Status

Current state: "Under Discussion"

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Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

Motivation

When processing an Incremental Alter Config on a Config entry of type List with OpType.SUBTRACT
the metadata passed to  AlterConfigPolicy.validate contains

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As discussed on the dev mailing list, to avoid introducing a potentially breaking change in 3.9.2, this KIP proposes to fix the the adoption of a flag to control the policy behavior.

Public Interfaces

Add a new boolean configuration for kafka servers

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The default value would be false, meaning nothing changes in 3.9.2. Conversely, setting it to true would align the behavior with KRaft policy validation

Proposed Changes

If the server config entry

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If the property is not explicitly set to true, then the existing behaviour is preserved.

Compatibility, Deprecation, and Migration Plan

• What impact (if any) will there be on existing users?
  • none as the configration would be false by default
• If we are changing behavior how will we phase out the older behavior?
  • not planned as Zookeper mode is phased out

Test Plan

Junit testing leveraging the @ClusterTest extension

Rejected Alternatives

Implementing the ZkAdminManager fix as a default behavior was rejected through PR and mailing list discussion, where backward compatibility was preferred to correctness.

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