Status

Current state: "Under Discussion"  Accepted

Discussion thread: here 

JIRA: here 

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MirrorMaker should not clear topic configurations that are excluded from replication.

In addition, source and target topic configurations could have different default values. Currently, Mirrormaker overwrites configurations on target topic even if the configurations on the source topic have not been changed but happened to have different default values. However, user may only want to sync configurations that they have changed but leave the ones with default values. 

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Public Interfaces

A new method will be added to ConfigPropertyFilter.

public interface ConfigPropertyFilter extends Configurable, AutoCloseable {
  boolean shouldReplicateSourceDefault(String prop);
}      

Proposed Changes

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

It also proposes adding the ability to choose using target cluster's default or source cluster's default for target topic configurations. For instance, users would be able to configure ConfigPropertyFilter to check if the configuration on the source topic is the default and decide whether or not to replicate it to the target topic.

Proposed Changes

1) Extend ConfigPropertyFilter  class to have a new method called shouldReplicateSourceDefault which would always return false by default. User would be able to configure this method to return true in order to replicate source cluster's configurations with default values. 

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• A new configuration setting to MirrorMaker:
  • Name: use.incremental.alter.configs

• • Description: Deprecated. Whether to automatically use the IncrementalAlterConfigs API for syncing topic configurations. This configuration will be removed in Kafka 4.0 and the IncrementalAlterConfigs API will be used by default. Users should make sure that the target cluster is running

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• • Kafka 2.3.0 or later. 

• • Type: String

• • Default: requested

• • When set to "requested", MirrorMaker will use the IncrementalAlterConfigs for syncing topic configurations. If

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• • any request receives an error from an incompatible broker, it will fallback to the deprecated AlterConfigs API for the subsequent calls and log a WARN message e.g. "The target cluster <ALIAS> is not compatible with IncrementalAlterConfigs API. Therefore using deprecated AlterConfigs API for syncing topic configurations"

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• • .

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• • When explicitly set to "never", MirrorMaker will use the deprecated AlterConfigs API for syncing topic configurations.

• • When explicitly set to "required", MirrorMaker will use the IncrementalAlterConfigs 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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Currently if users delete a topic configuration in the source cluster, it gets also deleted from the target cluster due to the replace all behaviour of AlterConfigs API. However with IncrementalAlterConfigs, the topic configuration in the target cluster would potentially be left unchanged. Therefore the default topic configuration on the source cluster will explicitly be cleared from the target cluster via Delete operation when using IncrementalAlterConfigs API. 

The KIP also proposes adding the ability for users to choose between target cluster's default or source cluster's default when using IncrementalAlterConfigs for syncing topic configurations. For instance, users would be able to configure ConfigPropertyFilter to choose whether or not to replicate the default configurations of the source topic to the target cluster. This gives users a bit more control in how they want to replicate their topic configurations. 

• Extend ConfigPropertyFilter class to have a new method called shouldReplicateSourceDefault which will return false by default. If set to false while using IncrementalAlterConfigs API, the default configurations in the source cluster will explicitly be cleared from the target cluster using the Delete operation. User will be able to configure this method to return true in order to include source cluster's default configurations in the replication. 

• Extend DefaultConfigPropertyFilter with a new property "use.defaults.from" that accepts "source" or "target" values. This will allow users to control which cluster's defaults get applied on the target. The user can also use the existing "config.properties.exclude" property to exclude configuration from the replication regardless of which cluster's default is chosen. 

Compatibility, Deprecation, and Migration Plan

By default, the new setting will be set to "requiredrequested"  which means we'll use IncrementalAlterConfigs if possible, and fallback to AlterConfigs API if incompatible. 

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