Logstash default document type from logs to doc

Elastic Stack Logstash
3

Thanks for the reply Ry,
my question was more related to how to guarantee a smooth transition if I make the upgrade at some point in time say x.

I would like to avoid the condition where messages indexed before x have logs as type and messages indexed after x have type doc.

This is how I was thinking to modify the logstash configuration file, given that x is some point in time on 6th February and new indexes are created at night when @timestamp hour is 01:00

filter{
...

  if [@metadata][type] == "system_logs"
  {
    mutate{
      # enable timestamp comparison adding a new field
      add_field => { "str_dt_new" => "2020-02-07T01:00:00.000Z"}
    }
    date {
      match => ["str_dt_new", "YYYY-MM-dd'T'HH:mm:ss.SSSZ"]
      target => "constant_date"
    }
  }
  if [@timestamp] <= [constant_date] {
    mutate {
      # for consistency with messages sent before changing config file, in the 
      # same day (i.e. same ES index)
      replace => { "type" => "logs" }
    }
  }
  else {
    mutate {
      # required from LS v6.x
      replace => { "type" => "doc" }
    }
  }

}

Does it make sense to you?