The value of this setting should correspond to a node setting on one or more nodes in your cluster.

For example, you might have set

node.tag: myvalue

in your elasticsearch.yml file for one or more of your nodes. To match allocation in this case, set value to myvalue. Additonally, if you used one of the special attribute names _ip, _name, _id, or _host for key, value can match the one of the node ip addresses, names, ids, or host names, respectively.

There is no default value. This setting must be set by the user or an exception will be raised, and execution will halt.