Elasticsearch: Aggregate documents based on date range - elasticsearch

Question

I have a set of documents in ElasticSearch 5.5 with two date fields: start_date and end_date.
I want to aggregate them into date histogram buckets (ex: weekly) such that if the start_date < week X < end_date, then document would be in "week X" bucket.
This means that a single document might be in multiple buckets.
Consider the following concrete example: I have a set of documents describing company employees, and for each employee you have hire date and (optionally) termination date. I want to build date histogram of number of active employees for trailing twelve months.
Sample doc content:
{
"start_date": "2013-01-12T00:00:00.000Z",
"end_date": "2016-12-08T00:00:00.000Z",
"id": "123123123"
}
Is there a way to do this in ES?

Answer 1

I have found one way to do this, using filter aggregations (
https://www.elastic.co/guide/en/elasticsearch/reference/master/search-aggregations-bucket-filter-aggregation.html). If I need, say, 12 trailing months report, then I would create 12 buckets, where each bucket defines filter conditions, such as:
"bool":{
"must":[{
"range":{
"start_date":{
"lte":"2016-01-01T00:00:00.000Z"
}
}
},{
{
"range":{
"end_date":{
"gt":"2016-02-01T00:00:00.000Z"
}
}
}]
}
However, I feel that it would be nice if there was an easier way to do this, since if I want say trailing 365 days, that means I have to create 365 bucket filters, which makes resultant query very large.

Answer 2

I know this question is quite old but as it's still open I am sharing my knowledge on this. Also this question does not clearly explains that what kind of output is expected but still I think this can be achieved using the "Date Histogram Aggregation" and "Bucket Script Aggregation".
Here are the documentation links for both of these aggregations.
https://www.elastic.co/guide/en/elasticsearch/reference/5.5/search-aggregations-bucket-datehistogram-aggregation.html
https://www.elastic.co/guide/en/elasticsearch/reference/5.5/search-aggregations-pipeline-bucket-script-aggregation.html