Add and Remove nodes in your cluster

When you start an instance of Elasticsearch, you are starting a node. An Elasticsearch cluster is a group of nodes that have the same cluster.name attribute. As nodes join or leave a cluster, the cluster automatically reorganizes itself to evenly distribute the data across the available nodes.

If you are running a single instance of Elasticsearch, you have a cluster of one node. All primary shards reside on the single node. No replica shards can be allocated, therefore the cluster state remains yellow. The cluster is fully functional but is at risk of data loss in the event of a failure.

You add nodes to a cluster to increase its capacity and reliability. By default, a node is both a data node and eligible to be elected as the master node that controls the cluster. You can also configure a new node for a specific purpose, such as handling ingest requests.

When you add more nodes to a cluster, it automatically allocates replica shards. When all primary and replica shards are active, the cluster state changes to green.

Enroll nodes in existing cluster

When Elasticsearch starts for the first time, the security auto-configuration process binds the HTTP layer to 0.0.0.0, but only binds the transport layer to localhost. This intended behaviour ensures that you can start a single-node cluster with security enabled by default without any additional configuration.

<aside> 💡 To add a node to a cluster running on multiple machines, you must also set discovery.seed_hosts so that the new node can discover the rest of its cluster.

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Before enrolling a new node, additional actions such as binding to an address other than localhost or satisfying bootstrap checks are typically necessary in production clusters.

Only nodes on the same host can join the cluster without additional configuration. If you want nodes from another host to join your cluster, you need to set transport.host to a supported value

To enrol new nodes in your cluster, create an enrolment token with the elasticsearch-create-enrollment-token tool on any existing node in your cluster. You can then start a new node with the --enrollment-token parameter so that it joins an existing cluster.

1. In a separate terminal from where Elasticsearch is running, navigate to the directory where you installed Elasticsearch and run the elasticsearch-create-enrollment-token tool to generate an enrolment token for your new nodes.

bin\\elasticsearch-create-enrollment-token -s node

Copy the enrolment token, which you’ll use to enrol new nodes with your Elasticsearch cluster.