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

MM2 internal topic names (heartbeats, checkpoints and offset-syncs) are hardcoded in the source code which makes it hard to run MM2 with any Kafka Cluster that has rules around topic’s naming convention and doesn’t allow auto-creation for topics. In this case you will need to create these internal topics up-front manually and make sure they do follow the cluster rules and guidance for topic creation, so MM2 should have flexibility to let you override the name of internal topics to follow the one you create.

Public Interfaces and Proposed Changes

This KIP proposes adding a new interface named InternalTopicNamingPolicy that defines how MM2 internal topics are named based on some new configuration.

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• heartbeatsTopic() → heartbeats
• checkpointTopic(clusterAlias)→ clusterAlias.checkpoint.internal
• offsetSyncTopic(targetCluster) → mm2-offset-syncs.targetCluste.internal

Source Connect and Checkpoint Task

In line with this proposal’s motivation we will also need to update MirrorSourceConnector and MirrorCheckpointTaskto ignore replicate or store checkpoints for internal topics.

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public class MirrorCheckpointTask extends SourceTask {
    ..
    boolean shouldCheckpointTopic(String topic) {
            return topicFilter.shouldReplicateTopic(topic) && !internalTopicNamingPolicy.isInternalTopic(topic);
        }
}

public class MirrorSourceConnector extends SourceConnector {
    ...
    boolean shouldReplicateTopic(String topic) {
            return (topicFilter.shouldReplicateTopic(topic) || isHeartbeatTopic(topic))
                && !internalTopicNamingPolicy.isInternalTopic(topic) && !isCycle(topic);
        }
}

Compatibility, Deprecation, and Migration Plan

When users upgrade an existing MM2 cluster they don’t need to change any of their current configuration as this proposal maintains the default behaviour for MM2.

Rejected Alternatives

Use the ReplicationPolicy and replication.policy.separator to control the naming convention for internal topics. Reason to reject: Since not all of the internal topics are not replicated it makes more sense to control them from a different interface.