title: Elasticsearch mapping not working
body: <p>Trying to create mapping under Elasticsearch 2 with the following command, but it fails:</p>
  
  <pre><code>POST /my_blog    
  {
      "settings": {
          "index" : {
              "number_of_shards" : 10
          }
      },     
      "mappings": {
          "post" : {        
              "_routing" : {
                  "required": false,
                  "path" : "post_date"
              },
              "properties": {
                  "user_id" :{
                      "type": "integer"                    
                  },
                  "post_text" : {
                      "type": "string"                    
                  },
                  "post_date": {
                      "type" : "date",
                      "format" : "YYYY-MM-DD"
                  }
              }
          }
      }
  }
  </code></pre>
  
  <p>Response:</p>
  
  <pre><code>{
     "error": {
        "root_cause": [
           {
              "type": "mapper_parsing_exception",
              "reason": "Mapping definition for [_routing] has unsupported parameters:  [path : post_date]"
           }
        ],
        "type": "mapper_parsing_exception",
        "reason": "mapping [post]",
        "caused_by": {
           "type": "mapper_parsing_exception",
           "reason": "Mapping definition for [_routing] has unsupported parameters:  [path : post_date]"
        }
     },
     "status": 400
  }
  </code></pre>
  
  <p>It doesn't matter what field I choose for the path, integer/string or date, it always gives the same error reply (see above). Any ideas?</p>