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https://issues.apache.org/jira/browse/KAFKA-15262?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17895920#comment-17895920
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Kanalas Vidor commented on KAFKA-15262:
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[~blacktooth] technically you are right, the MirrorHearbeatConnector is
producing into the target topic. However, if you check [Code
Ref,|https://github.com/apache/kafka/blob/ed44bcd71b3b9926c474033882eaa6c1cf35cfa4/connect/mirror/src/main/java/org/apache/kafka/connect/mirror/MirrorMakerConfig.java#L127]
by default (if global heartbeating is enabled), a herder is created for all
cluster pairs, regardless whether there is a replication flow enabled for those
two cluster pairs.
In other words, the MirrorHearbeatConnector of the replication flow A->B will
produce into B, however by the way MirrorMaker is working, there will be also a
MirrorHearbeatConnector for a (possibly not even enabled) replication flow
B->A which will produce into A. So the heartbeats topic on both A and B will be
populated.
> MirrorHeartbeatConnector is not working as documented
> -----------------------------------------------------
>
> Key: KAFKA-15262
> URL: https://issues.apache.org/jira/browse/KAFKA-15262
> Project: Kafka
> Issue Type: Bug
> Components: mirrormaker
> Affects Versions: 2.8.0, 3.4.0, 3.5.0
> Reporter: Ravindranath Kakarla
> Priority: Major
>
> As per the MM2
> [KIP-382|[https://cwiki.apache.org/confluence/display/KAFKA/KIP-382%3A+MirrorMaker+2.0]]
> the MirrorHeartbeatConnector should emit pings to heartbeat topic on the
> source cluster which then gets replicated to the target cluster. This can be
> used to demonstrate that MM2 is replicating the data.
> However, this is not happening right now. To the contrary, the
> MirrorHeartbeatConnector is producing heartbeat pings to target cluster
> instead of source. This is not much useful as it won't help detect problems
> connecting to source cluster or with the data replication.
> Is my understanding of the MirrorHeartbeatConnector accurate?
> *Reference:*
> _MM2 emits a *heartbeat* *topic* in each source cluster, which is replicated
> to demonstrate connectivity through the connectors. Downstream consumers can
> use this topic to verify that a) the connector is running and b) the
> corresponding source cluster is available. Heartbeats will get propagated by
> source and sink connectors s.t. chains like backup.us-west.us-east.heartbeat
> are possible._
> [Code
> Ref|https://github.com/apache/kafka/blob/ed44bcd71b3b9926c474033882eaa6c1cf35cfa4/connect/mirror/src/main/java/org/apache/kafka/connect/mirror/MirrorHeartbeatTask.java#L65]
>
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