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There is also documentation on the MirrorMaker at https://kafka.apache.org/documentation.html#basic_ops_mirror_maker.

How to set up a mirror

Setting up a mirror is easy - simply start up the mirror-maker processes after bringing up the target cluster. At minimum, the mirror maker takes one or more consumer configurations, a producer configuration and either a whitelist or a blacklist. You need to point the consumer to the source cluster's ZooKeeper, and the producer to the mirror cluster's ZooKeeper (or use the broker.list parameter).

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