multiline_filter.conf

      <match kubernetes.**>
        @type rewrite_tag_filter
        @id id_rewrite_tag_filter.multiline
        <rule>
          key fluentd_multiline
          pattern /^false$/
          tag plain.${tag}
        </rule>
        <rule>
          key fluentd_multiline
          pattern /^false$/
          invert true
          tag multiline.${tag}
        </rule>
      </match>
      <match multiline.**>
        @type relabel
        @label @multiline
      </match>
      <match plain.**>
        @type relabel
        @label @output
      </match>