An Elasticsearch cluster is a physical and a logical partition of the nodes that are allocated into it. Initially, you don't need to do any configuration for your cluster. When a node is started, Elasticsearch creates a directory based on the defined cluster name and then the node is allocated to this directory. In the background, Elasticsearch created some shards, and probably replicas as well (unless otherwise noted), when you created an index. The generated shards are also allocated in the same node.
Elasticsearch is built to scale. It will be sufficient to increase the number of nodes when more capacity is needed. In this case, the cluster will reorganize itself to take advantage of the extra hardware and will distribute the load. Elasticsearch provides clustering in a good manner, and this ability is one of the most important advantages.
In the following section, we will look closely at the basic components of an Elasticsearch cluster.
