=== How Primary and Replica Shards Interact
For explanation purposes, let's((("shards", "interaction of primary and replica shards")))((("primary shards", "interaction with replica shards")))((("replica shards", "interaction with primary shards"))) imagine that we have a cluster
consisting of three nodes. It contains one index called blogs that has
two primary shards. Each primary shard has two replicas. Copies of
the same shard are never allocated to the same node, so our cluster
looks something like <
[[img-distrib]] .A cluster with three nodes and one index image::images/elas_0401.png["A cluster with three nodes and one index"]
We can send our requests to any node in the cluster.((("nodes", "sending requests to"))) Every node is fully
capable of serving any request. Every node knows the location of every
document in the cluster and so can forward requests directly to the required
node. In the following examples, we will send all of our requests to Node 1,
which we will refer to as the requesting node.
TIP: When sending requests, it is good practice to round-robin through all the nodes in the cluster, in order to spread the load.