Logstash converts singleton array to string

Elastic Stack Logstash
1

I'm using

mutate {
    add_field => { "new_field" => ["X"] }
  }

to create an array of integers which can be appended to downstream.

But logstash output reads as "new_field" => "X".

2

This only works if you add more than 1 value. Then it will convert to an array.

mutate {
    add_field => { "new_field" => "x" }
  }

mutate {
    add_field => { "new_field" => "y" }
  }

That will create new_field: [ x, y ]

If you only want to create an array with 1 item then I use Ruby. All you are really doing is setting a new field with a value and wrapping in [ ].

  ruby {
    code => "event.set('new_field', [event.get('old_field')])"
  }

or

  ruby {
    code => "event.set('new_field', ['X'])"
  }
3

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