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Currently Mirrormaker uses deprecated alterConfigs  API when syncing topic configurations for broker compatibility to 0.11.0. However, the deprecated alterConfigs()   API API replaces any existing configuration with the new configuration. Due to this, additional configurations set on a remote topic get cleared up when MirrorMaker syncs topic configurations even if the configurations are filteredwhether they are filter or not.  For example this prevents running Cruise Control on the target cluster as it may set follower.replication.throttled.replicas and leader.replication.throttled.replicas.

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This KIP proposes to migrate to incrementalAlterConfigs  API for syncing topic configurations in MirrorMaker. The incrementalAlterConfigs  API  API has been around for several years since it was introduced in Kafka 2.3.0 and addresses the shortcoming of the deprecated alterConfigs  API. In order not to not break the compatibility, we will introduce a new configuration setting to MirrorMaker connector to give the option to enable incrementalAlterConfigs API for syncing topic configurations. This new configuration setting is expected to serve as a temporary measure until the next major release when the API is always used. 

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When set to false, MirrorMaker will keep using deprecated alterConfigs API for syncing topic configurations.

When explicitly set to true, MirrorMaker will use incrementalAlterConfigs API  API for syncing topic configurations. If it receives an error from an incompatible broker, the MirrorMaker will report this to the user and fail the connector. 

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4) From Kafka 4.0, syncTopicConfigs() will only call  updateTopicConfigsUsingIncrementalAlterConfigs() by default. The existing updateTopicConfigs() will method will be removed.

Compatibility, Deprecation, and Migration Plan

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(Is it necessary to add system tests?)

Rejected Alternatives

• We could have changed the current updateConfigs() method to call describeConfigs API before alterConfigs  so that it had an incremental mode. This would have avoided migrating to incrementalAlterConfigs API and adding a new configuration setting to MirrorMaker.  Howeverthe migration, however, the topics configurations could change between describeConfigs  and alterConfigs  calls so we could still end up applying syncing incorrect topic configurations.  We would need to stop using the  the deprecated API at some point anyway.