http://xx.xx.xx.1:9200/_cat/shards

myindex              2 r STARTED 16584778   1.4gb xx.xx.xx.2 node2
myindex              2 p STARTED 16584778   1.4gb xx.xx.xx.1 node1
myindex              1 r STARTED 16592755   1.4gb xx.xx.xx.2 node2
myindex              1 p STARTED 16592755   1.4gb xx.xx.xx.1 node1
myindex              3 r STARTED 16592009   1.4gb xx.xx.xx.2 node2
myindex              3 p STARTED 16592033   1.4gb xx.xx.xx.1 node1
myindex              0 r STARTED 16610776   1.3gb xx.xx.xx.2 node2
myindex              0 p STARTED 16610776   1.3gb xx.xx.xx.1 node1

http://xx.xx.xx.1:9200/_cluster/reroute?explain

{
    "commands" : [
        {
            "move" : {
                "index" : "myindex",
                "shard" : 1,
                "from_node" : "node1",
                "to_node" : "node2"
            }
        },
        {
            "allocate_replica" : {
                "index" : "myindex",
                "shard" : 1,
                "node" : "node1"
            }
        }
    ]
}

{
    "decider": "same_shard",
    "decision": "NO",
    "explanation": "the shard cannot be allocated on the same node id [xxxxxxxxxxxxxxxxxxxxxx] on which it already exists"
},