title: How to use ingest pipelines on already indexed documents?
body: <p>I've been using FOSElasticaBundle to index my documents (which are entities from a Symfony project kept in a db through Doctrine) into Elastic Search. FOSElastica does an automatic mapping and index after that all the documents.</p>
  
  <p>The problem is that there's some actions I would want to apply on every documents (on those already indexed and those which will be after), so pipelines and painless seems to be a good solution.</p>
  
  <p>But, I can't get to understand how to apply a pipeline to documents that are already indexed, do you have an idea how ?</p>
  
  <p>I've seen that you can add a "pipeline=my_pipeline_name" after an ES request but you can do it for a single document while I'd want it to affect all the documents.</p>