A R3Search cluster contains three primary components: core MediaBeacon, shards, and Zookeepers.
Runs the user interface and serves as the central hub for all R3Search nodes and Zookeepers.
Each shard is hosted on its own separate R3Search node, forming the cluster. There are two types of shards, leaders and slaves. Information is split across all the leaders and the Zookeepers track which leader has what info. Slaves under each leader are an exact copy of the data contained within its leader. (Multiple shards are not necessary for R3Search clustering.)
Each leader that exists increases R3Search’s ability to handle a large user load while additional slaves increase replication. See the diagram below for an example. Your setup can contain more or less leaders and slaves than what is depicted.
Zookeepers help track which leader shard has which data. It’s important that if multiple Zookeepers exist, they are in an odd quantity. See the Redundancy in a Cluster section for more info.