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Redis Cluster doesn't have primary and replicas for each slot (the way that Streams has primary and standbys for each task). Rather, it has primary and replicas for each node . Thus, if there are two nodes, A and B with replicas Ar and Br, the node Ar is responsible for replicating the exact same set of slots that are assigned to A, and likewise with B and Br. This simplifies the assignment considerations somewhat, as a given node only  needs to host active (primary) copies or  passive (replica) copies. The replicas can serve queries if the query specifies that it accepts stale data, but most likely this arrangement results in the replica nodes being underutilized. So, my quick judgement is that the simplicity of this arrangement is enviable, but we probably don't want to follow suit.

reference: https://redis.io/topics/cluster-spec

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Old Version of KIP-441

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