code: public void setAutoscalerCallback(Action1<AutoScaleAction> callback) throws IllegalStateException {
          checkIfShutdown();
          if (autoScaler == null) {
              throw new IllegalStateException("No autoScaler setup");
          }
          autoScaler.setCallback(callback);
      }
docs: Set the autoscale call back action. The callback you pass to this method receives an indication when an
  autoscale action is to be performed, telling it which autoscale rule prompted the action and whether the
  action is to scale up or scale down the autoscale group. The callback then initiates the appropriate
  scaling actions.
  
  @param callback the callback to invoke for autoscale actions
  @throws IllegalStateException if no autoscaler was established
  @see <a href="https://github.com/Netflix/Fenzo/wiki/Autoscaling">Autoscaling</a>