title: Average request duration using Prometheus
body: <p>I have deployed the Istio Bookinfo application in a Kubernetes cluster. Following the documentation, I'm trying to measure the average request duration using the following query:</p>
  
  <pre><code>rate(istio_request_duration_milliseconds_sum[1m]) / rate(istio_request_duration_milliseconds_count[1m])
  </code></pre>
  
  <p>This query returns me "doubled" results i.e. for each request I get two results, with different <em>Value</em> but same <em>source</em> and <em>destination</em>, one labelled as <em>reporter="source"</em> and the other as <em>reporter="destination"</em>. I was not able to find any clarification about it and I have not clear how these measures work. Why I have two values returned?</p>