What about scaling as the demand for our application grows? If we start a third node, our cluster reorganizes itself to look like A three-node cluster — shards have been reallocated to spread the load.
One shard each from Node 1 and Node 2 have moved to the new
Node 3 and we have two shards per node, instead of three.
This means that the hardware resources (CPU, RAM, I/O) of each node
are being shared between fewer shards, allowing each shard to perform
better.
A shard is a fully fledged search engine in its own right, and is capable of using all of the resources of a single node. With our total of 6 shards (3 primaries and 3 replicas) our index is capable of scaling out to a maximum of 6 nodes, with one shard on each node and each shard having access to 100% of its node’s resources.