title: Can you trigger autoscaling in Google App Engine based on Cloud Pub/Sub queue?
body: <p>I know you can configure autoscaling based on queue size when scaling a Compute Engine instance group, but I'm unsure of how I could replicate this behavior in a flexible App Engine based environment. Is this possible?</p>
  
  <p>I want to be able to decouple my frontend service from my backend and allow them to work asynchronously, but I'm not sure how to scale the backend with  pub/sub queue size that can get very big. The only scaling options I see in <code>autoscaling</code> section of <code>app.yaml</code> have to do with CPU utilization. </p>