查看未分配的分片

curl -XGET localhost:9200/_cat/shards?h=index,shard,prirep,state,unassigned.reason| grep UNASSIGNED

查看分片未分配原因

curl -XGET localhost:9200/_cluster/allocation/explain?pretty

打开集群分片再分配开关，默认开启

curl -X PUT "localhost:9200/_cluster/settings?pretty" -H 'Content-Type: application/json' -d'
{
    "transient" : {
        "cluster.routing.allocation.enable" : "all"
    }
}
'

参考链接：
https://www.datadoghq.com/blog/elasticsearch-unassigned-shards/