title: ElasticSearch intermittent blank responses (cluster status: yellow)
body: <p>I am using ElasticSearch (based off of Lucene) for searches.  Every now and then over the past month or so since switching, I have had users get no results on a query.  If they refresh, the results will be populated.  Looking into the log I don't see any errors, so I am assuming that ElasticSearch just can't access the index on occasion.</p>
  
  <p>This isn't when I am indexing large amounts of documents either.  Is there something I can add to the settings that will help me better debug this?  Would it help to tweak the configuration or add another cluster or node?</p>
  
  <p>If I check my Admin Cluster Health, it is a yellow status.  Would resolving this help my issue?</p>
  
  <pre><code>{
    "cluster_name" : "xxxxx",
    "status" : "yellow",
    "timed_out" : false,
    "number_of_nodes" : 1,
    "number_of_data_nodes" : 1,
    "active_primary_shards" : 5,
    "active_shards" : 5,
    "relocating_shards" : 0,
    "initializing_shards" : 0,
    "unassigned_shards" : 5
  }
  </code></pre>