blablabla.rb

> yell/lib/yell/event.rb 

def request_id
  env['action_dispatch.request_id']
end

> yell-adapters-gelf/lib/yell/adapters/gelf.rb

      write do |event|
        message = format({
          'version'   => '1.0',

          'facility'  => facility,
          'level'     => Severities[event.level],
          'timestamp' => event.time.to_f,
          'host'      => source || event.hostname,
>>>>>>>>  'request_id' => event.request_id,
          'file'      => event.file,
          'line'      => event.line,
          '_method'   => event.method,
          '_pid'      => event.pid
        }, *event.messages )