title: Should Elastic Search be reindexed if I make any configuration changes to Logstash
body: <p>If I make any configuration changes to Logstash.
  Will I see the chnages applied to Elastic Search
  For Example
  If I change the grok pattern and added new Fields,
  Will I be able to see the chnages effected on already indexed logs in elastic search.</p>
  
  <p>If not what should I do?
  Should I re-index whole old logs which are already indexed again to see the new fields??</p>