Cluster Reroute

The reroute command allows to explicitly execute a cluster reroute allocation command including specific commands. For example, a shard can be moved from one node to another explicitly, an allocation can be canceled, or an unassigned shard can be explicitly allocated on a specific node.

Here is a short example of how a simple reroute API call:

curl -XPOST 'localhost:9200/_cluster/reroute' -d '{
    "commands" : [ {
        "move" :
            {
              "index" : "test", "shard" : 0,
              "from_node" : "node1", "to_node" : "node2"
            }
        },
        {
          "allocate" : {
              "index" : "test", "shard" : 1, "node" : "node3"
          }
        }
    ]
}'

An important aspect to remember is the fact that once when an allocation occurs, the cluster will aim at re-balancing its state back to an even state. For example, if the allocation includes moving a shard from node1 to node2, in an even state, then another shard will be moved from node2 to node1 to even things out.

The cluster can be set to disable allocations, which means that only the explicitly allocations will be performed. Obviously, only once all commands has been applied, the cluster will aim to be re-balance its state.

Another option is to run the commands in dry_run (as a URI flag, or in the request body). This will cause the commands to apply to the current cluster state, and return the resulting cluster after the commands (and re-balancing) has been applied.

The commands supported are: