Elasticsearch nodes
An Elasticsearch node is a single running instance of Elasticsearch. A single physical or virtual machine can run multiple instances or nodes of Elasticsearch, assuming it has sufficient resources to do so.
Elasticsearch nodes perform a variety of roles within the cluster. The roles that a node performs can be granularly controlled as required.
We will cover some common node roles in the following sections.
Master-eligible nodes
Master-eligible nodes take part in the master election process. At any point in time, a single node is elected to be the active master. The active master node keeps track of other nodes in the cluster, creation or deletion of indices, shards being allocated to nodes based on requirements/constraints, cluster settings being applied, and more.
The master role is generally not very resource-intensive and can be co-located on a node running other roles in smaller clusters. Running the master role on a dedicated host makes sense...
