To better understand the following sections, knowledge of the basic concepts such as application node and cluster are required.

One or more Elasticsearch nodes can be setup on physical or a virtual server depending on the available resources such as RAM, CPUs, and disk space.

A default node allows us to store data in it and to process requests and responses. (In Chapter 2, Downloading and Setup, we will see details on how to set up different nodes and cluster topologies).

When a node is started, several actions take place during its startup: such as:

After node startup, the node searches for other cluster members and checks its index and shard status.

To join two or more nodes in a cluster, these rules must be matched:

The network must be configured to support broadcast discovery (default) and they can communicate with each other. (Refer to How to setup networking recipe Chapter 2, Downloading and Setup).

A common approach in cluster management is to have one or more master nodes, which is the main reference for all cluster-level actions, and the other ones called secondary, that replicate the master data and actions.

To be consistent in write operations, all the update actions are first committed in the master node and then replicated in secondary ones.

In a cluster with multiple nodes, if a master node dies, a master-eligible one is elected to be the new master. This approach allows automatic failover to be setup in an Elasticsearch cluster.

In Elasticsearch, we have four kinds of nodes:

In big cluster architectures, having some nodes as simple client nodes with a lot of RAM, with no data, reduces the resources required by data nodes and improves performance in search using the local memory cache of them.