Elasticsearch lets us tune it by specifying various parameters in the elasticsearch.yml file. But you should treat this file as the set of default values that can be changed in the runtime using the Elasticsearch REST API.

In order to set one of the properties, we need to use the HTTP PUT method and send a proper request to the _cluster/settings URI. However, we have two options: transient and permanent property settings.

The first one, transient, will set the property only until the first restart. In order to do this, we will send the following command:

curl -XPUT 'localhost:9200/_cluster/settings' -d '{
  "transient" : {
    "PROPERTY_NAME" : "PROPERTY_VALUE"
  }
}'

As you can see, in the preceding command, we used the object named transient and we added our property definition there. This means that the property will be valid only until the restart. If we want our property settings to persist between restarts, instead of using the object named transient, we will...