POST _reindex
{
  "source": {
    "remote": {
      "host": "http://老ES地址:9200",
      "username": "老ES用户名",
      "password": "老ES密码"
    },
    "index": "老索引名"
  },
  "dest": {
    "index": "新索引名"
  },
  "headers": {
    "Authorization": "Basic 新ES的Base64认证串"
  }
}

elasticsearch.yml添加白名单：
reindex.remote.whitelist:
  - "192.168.0.*:9200"