Status

Current state: Under Discussion

Discussion thread: here

JIRA: KAFKA-13365

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

Motivation

As of present, MirrorMaker 2 (aka MM2) 's client configurtaion feature has some problems:

1. The replication-level client configuration works only to the common properties like bootstrap.servers, security.protocol, ssl, sasl, etc; that is, a configuration like 'A→B.producer.batch.size' is ignored.
   1. Also, which admin client is affected by the replication-level configuration like A→B.admin.retry.backoff.ms is unclear; MM2 uses two admin clients for both upstream and downstream clusters, respectively.
2. MM2 is based on Kafka Connect framework's connector; Since MM2 Connectors (MirrorSourceConnector, MirrorCheckpointConnector, and MirrorHeartbeatConnector) are source connectors, they use producer instance created by Kafka Connector, which uses 'producer.override.{property-name}' in connector configuration; But, 'target.producer.{property-name}' are not automatically applied to 'producer.override.{property-name}' so not actually applied to producer instance.
3. MM2 requires to define the 'bootstrap.servers' of the clusters in cluster-level, like 'A.bootstrap.servers' or 'B.bootstrap.servers'; but it also allows to override them in cluster-level and replication-level configs, like 'A.producer.bootstrap.servers' or 'A→B.consumer.bootstrap.servers'; actually these configurations are not used but, it would be better to ignore it and give a warning.

For the proof of the problem, please refer here.

Public Interfaces

This proposal does not introduce any new public interface or configurable settings; it only makes the existing ones (which are currently ignored by MirrorMaker 2) working by providing consistent, easy-to-understand configuration rules.

Proposed Changes

1. The replication-level client configuration now works; A->B.producer.{property-name} and A->B.admin.{property-name} are applied to target cluster clients and A->B.consumer.{property-name} is applied to source cluster clients.
2. In standalone mode, target.producer.{property-name} is automatically copied to producer.override.{property-name}. In connector mode, the user should manually configure them, and the documentation will explicitly mention it.
3. Cluster-level and replication-level client bootstrap servers configurations will be ignored and show a warning message.

Compatibility, Deprecation, and Migration Plan

Since this proposal only makes currently not working settings work, there is no deprecation or migration plan.

Rejected Alternatives

None.