Need @timestamp value where the maximum aggregation result occurred

[silentfilm (Bruce Calvert)]

I'm using an Elasticsearch query (6.7) to find the maximum number of records returned for a particular service. My aggregation query is working great, but I need to also find the time when this maximum occurred.

If I specify docvalue_fields or just look in _source, I can see the @timestamp in the query results. However, I only need the maximum value(s) and when these maximums were returned. Is there any way to do this?

{
"size": 0,
"query": {
    "bool": {
        "must": [
            {
                "terms": {
                    "source": [
                        "export",
                        "collection"
                    ]
                }
            },
            {
                "match": {
                    "name": "COLLECTION.RecsReceived"
                }
            },
            {
                "match": {
                    "component": "DATA"
                }
            },
            {
                "range": {
                    "@timestamp": {
                        "gte": "now-14d"
                    }
                }
            },
            {
                "range": {
                    "count": {
                        "gt": 0
                    }
                }
            }
        ]
    }
},
"aggs": {
    "hostname_group": {
        "terms": {
            "field": "hostname.keyword"
        },
        "aggs": {
            "instance_group": {
                "terms": {
                    "field": "instance.keyword"
                },
                "aggs": {
                    "service_group": {
                        "terms": {
                            "field": "service.keyword"
                        },
                        "aggs": {
                                "records_received": {
                                    "max": {
                                        "field": "count"
                                    }
                                }
                            }
                        }
                    }
                }
            }
        }
    }
}

}

I get output like this (truncated):
{
"took": 10,
"timed_out": false,
"_shards": {
    "total": 7,
    "successful": 7,
    "skipped": 0,
    "failed": 0
},
"hits": {
    "total": 13116,
    "max_score": 0.0,
    "hits": []
},
"aggregations": {
    "hostname_group": {
        "doc_count_error_upper_bound": 0,
        "sum_other_doc_count": 0,
        "buckets": [
            {
                "key": "aln-dev",
                "doc_count": 13116,
                "instance_group": {
                    "doc_count_error_upper_bound": 0,
                    "sum_other_doc_count": 0,
                    "buckets": [
                        {
                            "key": "2",
                            "doc_count": 8207,
                            "service_group": {
                                "doc_count_error_upper_bound": 0,
                                "sum_other_doc_count": 2314,
                                "buckets": [
                                    {
                                        "key": "sms",
                                        "doc_count": 590,
                                        "records_received": {
                                            "value": 160.0
                                        }
                                    },
                                    {
                                        "key": "voice",
                                        "doc_count": 590,
                                        "records_received": {
                                            "value": 3778.0
                                        }
                                    },

[silentfilm (Bruce Calvert)]

Doing a terms aggregation and then a max aggregation did the trick:

    "aggs": {
    "hostname_group": {
        "terms": {
            "field": "hostname.keyword"
        },
        "aggs": {
            "instance_group": {
                "terms": {
                    "field": "instance.keyword"
                },
                "aggs": {
                    "service_group": {
                        "terms": {
                            "field": "service.keyword"
                        },
                        "aggs": {
                            "time_period": {
                                "terms": {
                                  "field": "@timestamp",
                                  "size": 1,
                                  "order": {
                                    "records_received": "desc"
                                  }
                                },
                                "aggs": {
                                    "records_received": {
                                        "max": {
                                            "field": "count"
                                        }
                                    }
                                }
                            }
                        }
                    }
                }
            }
        }
    }
}

}