Alias index routing not work

Elastic Stack Elasticsearch
1

I created two test index and one alias associated with them:

POST /_aliases
{
"actions" : [
    { 
      "add" : { 
        "index" : "test", 
        "alias" : "alias_test",
        "index_routing" : "1"
      }
    },
    {
      "add" : {
        "index" : "test2", 
        "alias" : "alias_test"
      }
    }
]
}

However, when I tried to index document to test index with routing=1, it still throw out an error:

POST alias_test/test/test?routing=1
{
"user" : "kimchy",
"post_date" : "2009-11-15T14:12:12",
"message" : "trying out Elasticsearch"   
}

Error message:

{
"error": {
  "root_cause": [
     {
        "type": "illegal_argument_exception",
        "reason": "Alias [alias_test] has more than one indices associated with it [[test2, test]], can't execute a single index op"
     }
  ],
  "type": "illegal_argument_exception",
  "reason": "Alias [alias_test] has more than one indices associated with it [[test2, test]], can't execute a single index op"
},
"status": 400
}
2

What version?