1, find out the reasons, to find not know the node, shard
http://localhost:9200/_cluster/allocation/explain?pretty
POST /_cluster/reroute?retry_failed=true
{
"commands" : [
{
"allocate_replica" : {
"index" : "myindex",
"shard" : 1,
"node" : "mynode"
}
}
]
}