Why in Elasticsearch as backend of Logstash all fields are of string type?

Question

elasticsearch

Hello.
We are introducing the ELK stack into the infrastructure, we decided to do a pilot launch on nginx access logs. We installed everything, set up the collection, but when it came to analytics, it turned out that it was impossible to do any arithmetic aggregations in Kibana, after a short trial it turned out that all fields in ES have type: string and because of this it is impossible to do Sum or Avg.
I specifically flipped through a bunch of tutorials on installing ELK, but the mappings are not explicitly written anywhere, from which I can conclude that people have the right types out of the box.
Question: what did we do wrong and how can this situation be corrected without losing the data already collected?

Answer 1

Option A: register the template in ElasticSearch
Option B: register the mutation in Logstash