title: Prometheus use of avg_over_time with absent
body: <p>we have started to use prometheus for monitoring our infrastructure. One service has the following alert configured:</p>
  
  <ul>
  <li>(absent(up{job="service"}) or (up{job="service"} == 0)+1) == 1</li>
  </ul>
  
  <p>With that, we receive alerts if "up" is zero or if no metrics are reachable.</p>
  
  <p>Now we want a grafana "single stat" panel that shows the "uptime" of the service, but "absent" can't be used with "avg_over_time", there is an option for including something like "absent" in our uptime's panel?</p>