What does @ mean in elastic search documents?

Question

My question is: "What does the @ mean in elastic search documents?" @timestamp automatically gets created along with @version. Why is this and what's the point?

Here is some context... I have a web app that writes logs to files. Then I have logstash forward these logs to elastic search. Finally, I use Kibana to visualize everything.

Here is an example of one of the documents in elastic search:

{
  "_index": "logstash-2018.02.17",
  "_type": "doc",
  "_id": "0PknomEBajxXe2bTzwxm",
  "_version": 1,
  "_score": null,
  "_source": {
    "@timestamp": "2018-02-17T05:06:13.362Z",
    "source": "source",
    "@version": "1",
    "message": "message",
    "env": "development",
    "host": "127.0.0.1"
  },
  "fields": {
    "@timestamp": [
      "2018-02-17T05:06:13.362Z"
    ]
  },
  "sort": [
    1518843973362
  ]
}

Answer 1

@ fields are usually ones generated by Logstash as metadata ones, @timestamp being the value that the event was processed by Logstash. Similarly @version is also being added by Logstash to denote the version number of the document.

Here is the reference.