如何分桶排序

mapping

{
  "index_product" : {
    "mappings" : {
      "_doc" : {
        "properties" : {
          "product" : {
            "type" : "nested",
            "properties" : {
              "id" : {
                "type" : "integer"
              },
              "name" : {
                "type" : "text"
              },
              "router" : {
                "type" : "keyword"
              }
            }
          }
        }
      }
    }
  }
}

数据

POST /index_product/_doc/1
{
  "product": [
    {
      "id": 1,
      "name": "Product A",
      "router": "z"
    },
    {
      "id": 2,
      "name": "Product B",
      "router": "c"
    },
    {
      "id": 3,
      "name": "Product C",
      "router": "e"
    }
  ]
}

需求

我有一个类似上述索引数据结构，目的是想对过ID分桶，然后按router排序，我的思路是如下写的，但是执行不成功，希望高人指点下

GET /index_product/_search
{
  "size": 0,
  "aggs": {
    "nested_products": {
      "nested": {
        "path": "product"
      },
      "aggs": {
        "product_buckets": {
          "terms": {
            "field": "product.id",
            "size": 10,
            "order": {
              "router_sort": "asc"   // 按router字段的升序排序
            }
          },
          "aggs": {
            "router_sort": {
              "terms": {
                "field": "product.router.keyword",   // 使用.keyword进行精确匹配，不分析字符串
                "size": 10,
                "order": {
                  "_key": "asc"   // 按router字段的升序排序
                }
              }
            }
          }
        }
      }
    }
  }
}

问题

{
  "error": {
    "root_cause": [
      {
        "type": "aggregation_execution_exception",
        "reason": "Invalid aggregation order path [router_sort]. Buckets can only be sorted on a sub-aggregator path that is built out of zero or more single-bucket aggregations within the path and a final single-bucket or a metrics aggregation at the path end."
      }
    ],
    "type": "search_phase_execution_exception",
    "reason": "all shards failed",
    "phase": "query",
    "grouped": true,
    "failed_shards": [
      {
        "shard": 0,
        "index": "index_product",
        "node": "CbXGx8QhRUu6ownsGF9gAA",
        "reason": {
          "type": "aggregation_execution_exception",
          "reason": "Invalid aggregation order path [router_sort]. Buckets can only be sorted on a sub-aggregator path that is built out of zero or more single-bucket aggregations within the path and a final single-bucket or a metrics aggregation at the path end."
        }
      }
    ]
  },
  "status": 500
}

期望

按ID分桶后，再按route字段按字母升序或降序