title: Prometheus how "up" metrics works
body: <p>I'm looking for information how "up" metrics is calculated by Prometheus</p>
  
  <pre><code>up{job="&lt;job-name&gt;", instance="&lt;instance-id&gt;"}: 1 if the instance is healthy, i.e. reachable, or 0 if the scrape failed.
  </code></pre>
  
  <p>How Prometheus calculate when</p>
  
  <blockquote>
    <p>the instance is healthy</p>
  </blockquote>
  
  <p>I'm using Apache Cassandra with Prometheus and from time to time "up" metrics showing "down". However Cassandra working OK.</p>