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
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
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.