title: Error by Opsworks : unable to find rds instance with ARN
body: <p>I'm creating an <code>opsworks</code> stack using a <code>cloudformation</code> template, and I have few applications in my stack that require a <code>database</code> RDS instance :</p>
  
  <pre><code>"WordpressApp": {
          "Type": "AWS::OpsWorks::App",
          "Properties": {
           "AppSource" : {
            "Type" : "git",
            "Url" : "git://github.com:myproject/wordpress.git",
            "Revision" : "master"
           },
           "DataSources":[{
            "Arn" : { "Ref" : "RDSInstanceARN" },
            "DatabaseName" : "application",
            "Type" : "RdsDbInstance"
           }],
           "Description": "website application",
           "Name" : "app",
           "Shortname" : "app",
           "StackId" : {"Ref": "MyStack"},
           "Type" : "php"
          }
      },
  </code></pre>
  
  <p>Here is the <code>RDSInstancARN</code> parameter : </p>
  
  <pre><code>"RDSInstanceARN" : {
      "Description" : "Arn of the RDS instance",
      "Type" : "String",
      "Default" : "arn:aws:rds:eu-west-1:454524154879:db:instanceappdb"
  }
  </code></pre>
  
  <p>The ARN is well written.
  When I test the template I get this error : </p>
  
  <pre><code>unable to find rds instance with ARN 
  </code></pre>
  
  <p>What is the cause of this error ? I don't understand, the arn is written properly and it exists in the aws account and running. Any idea please ? Thank you.</p>