title: Correct usage of describeInstances amazon ec2
body: <p>I am trying to use the describeInstances function in amazon ec2 to get details about my instance 
  using my tag id.  In the documentation it mentions use the filter,</p>
  
  <blockquote>
    <p>tag:key=value - The key/value combination of a tag assigned to the
    resource, where tag:key is the tag's key.</p>
  </blockquote>
  
  <p>I tried it in the following way:</p>
  
  <pre><code>var params1 = {
              Filters : [
                  {
                      Tags      : [ {
                          Key   : key_name,
                          Value : key_value
                      } ]
                  }
              ]
          };
  
  ec2.describeInstances(params1, function(data, err) {
  })
  </code></pre>
  
  <p>, but I get an error: Unexpected Token at Tags : 
  What is the correct way to use this api?</p>