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Add nodes to your cluster

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Add nodes to your cluster

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Up to this point, we have used a cluster with a single Elasticsearch node to get up and running with the Elastic Stack. An Elasticsearch node is a single server that is part of your cluster and stores pieces of your data called shards.

You can add more nodes to your cluster and optionally designate specific purposes for each node. For example, you can allocate master nodes, data nodes, ingest nodes, machine learning nodes, and dedicated coordinating nodes. For details about each node type, see Nodes.

In a single cluster, you can have as many nodes as you want but they must be able to communicate with each other. The communication between nodes in a cluster is handled by the transport module. To secure your cluster, you must ensure that the internode communications are encrypted.

In this tutorial, we add more nodes by installing more copies of Elasticsearch on the same machine. By default, Elasticsearch binds to loopback addresses for HTTP and transport communication. That is fine for the purposes of this tutorial and for downloading and experimenting with Elasticsearch in a test or development environment. When you are deploying a production environment, however, you are generally adding nodes on different machines so that your cluster is resilient to outages and avoids data loss. In a production scenario, there are additional requirements that are not covered in this tutorial. See Development vs production mode and Adding nodes to your cluster.

Let’s add two nodes to our cluster!

Install two additional copies of Elasticsearch. It’s possible to run multiple Elasticsearch nodes using a shared installation. In this tutorial, however, we’re keeping things simple by using the zip or tar.gz packages and by putting each copy in a separate folder. You can simply repeat the steps that you used to install Elasticsearch in the Getting started with the Elastic Stack tutorial.
Update the ES_PATH_CONF/elasticsearch.yml file on each node:
1. Enable the Elasticsearch security features.
2. Ensure that the nodes share the same cluster.name.
3. Give each node a unique node.name.
4. Specify the minimum number of master-eligible nodes that must be available to form a cluster. By default, each node is eligible to be elected as the master node and control the cluster. To avoid a split brain scenario where multiple nodes elect themselves as the master, use the discovery.zen.minimum_master_nodes setting.
By default, if you run multiple Elasticsearch nodes on the same machine, it automatically uses free ports in the range 9200-9300 for HTTP and 9300-9400 for transport. If you want to assign specific port numbers to each node, however, you can add TCP transport settings. You can then provide a list of these seed nodes, which is used to discover the nodes in your cluster.

For example, add the following settings to the ES_PATH_CONF/elasticsearch.yml file on the first node:
```
xpack.security.enabled: true
cluster.name: test-cluster
node.name: node-1
discovery.zen.minimum_master_nodes: 2
transport.tcp.port: 9301
discovery.zen.ping.unicast.hosts: ["localhost:9302", "localhost:9303"]
```
Add the following settings to the ES_PATH_CONF/elasticsearch.yml file on the second node:
```
xpack.security.enabled: true
cluster.name: test-cluster
node.name: node-2
discovery.zen.minimum_master_nodes: 2
transport.tcp.port: 9302
discovery.zen.ping.unicast.hosts: ["localhost:9301", "localhost:9303"]
```
Add the following settings to the ES_PATH_CONF/elasticsearch.yml file on the third node:
```
xpack.security.enabled: true
cluster.name: test-cluster
node.name: node-3
discovery.zen.minimum_master_nodes: 2
transport.tcp.port: 9303
discovery.zen.ping.unicast.hosts: ["localhost:9301", "localhost:9302"]
```
In these examples, we have not specified the transport.host, transport.bind_host, or transport.publish_host settings, so they default to the network.host value. If you have not specified the network.host setting, it defaults to _local_, which represents the loopback addresses for the system.

If you choose different cluster names, node names, host names, or ports, you must substitute the appropriate values in subsequent steps as well.
Start each Elasticsearch node. For example, if you installed Elasticsearch with a .tar.gz package, run the following command from each Elasticsearch directory:
```
./bin/elasticsearch
```
See Starting Elasticsearch.
(Optional) Restart Kibana. For example, if you installed Kibana with a .tar.gz package, run the following command from the Kibana directory:
```
./bin/kibana
```
See Starting and stopping Kibana.
Verify that your cluster now contains three nodes. For example, use the cluster health API:
```
GET _cluster/health
```
Confirm the number_of_nodes in the response from this API.

You can also use the cat nodes API to identify the master node:
```
GET _cat/nodes?v
```
The node that has an asterisk(*) in the master column is the elected master node.

Now that you have multiple nodes, your data can be distributed across the cluster in multiple primary and replica shards. For more information about the concepts of clusters, nodes, and shards, see Getting started with Elasticsearch.

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