Get latest document of each unique record

Elastic Stack Elasticsearch
1

We have about 300,000 unique customers. We have one document each for every order placed, so we have several million order documents since the past 3 years.

How can I get the latest order document for each unique customer's record?

{
"_id" : 1,
"customer_id" : 1001,
"order_amount" : 15.00,
"timestamp" : 1/1/2014,
},
{
"_id" : 2,
"customer_id" : 1001,
"order_amount" : 17.00,
"timestamp" : 1/1/2015,
},
{
"_id" : 3,
"customer_id" : 1002,
"order_amount" : 13.00,
"timestamp" : 1/1/2016,
}

I need the output to be records _id - 2 and 3. Is this possible at all?

2

Maybe parent/child? Index one parent document for each customer, and a child document for each order that customer has? But then I'm unsure at query time how to only retrieve e.g. the top 2 children per parent ... maybe using top hits aggregation, sorting by timestamp descending, keeping the top 2.

Mike McCandless