Cluster allocation explain

Field	Type	Description
current_node	String	If you only want an explanation if the shard happens to be on a particular node, specify that node name here.
index	String	The name of the shard’s index.
primary	Boolean	Whether to provide an explanation for the primary shard (true) or its first replica (false), which share the same shard ID.
shard	Integer	The shard ID that you want an explanation for.