anchor.diff:  
   `POST /_cluster/reroute`
   
  -
   [[cluster-reroute-api-desc]]
   ==== {api-description-title}
   
  
positive.code:     Allocate an unassigned replica shard to a node. Accepts `index` and `shard`
      for index name and shard number, and `node` to allocate the shard to. Takes
      <<modules-cluster,allocation deciders>> into account.
  --
  
  Two more commands are available that allow the allocation of a primary shard to
  a node. These commands should however be used with extreme care, as primary
  shard allocation is usually fully automatically handled by {es}. Reasons why a 
  primary shard cannot be automatically allocated include the
  following:
  
  
negative.code: another explicitly, an allocation can be cancelled, and an unassigned shard can
  be explicitly allocated to a specific node.
  
  It is important to note that after processing any reroute commands {es} will
  perform rebalancing as normal (respecting the values of settings such as
  `cluster.routing.rebalance.enable`) in order to remain in a balanced state. For
  example, if the requested allocation includes moving a shard from `node1` to
  `node2` then this may cause a shard to be moved from `node2` back to `node1` to
  even things out.
  
  The cluster can be set to disable allocations using the
  `cluster.routing.allocation.enable` setting. If allocations are disabled then
  the only allocations that will be performed are explicit ones given using the
  `reroute` command, and consequent allocations due to rebalancing.
  
  