Prioritize an host over the others

Hello,

When I define a multiple hosts list in the elasticsearch output plugin, is it possible to prioritize one host over the others ?
Can I affect a weight in order to redistribute essentially to one specific node and send requests on other nodes only when this node is down ?

I don't think that is possible. By default all nodes in same cluster will be active and data will be distributed on the shards which will spread across the nodes in the cluster. However you may want to look at "Routing" configurations. Refer to this blogpost.