title: Find Missing Logs with ELK
body: <p>I've just deployed ELK in an attempt to see if it can be used for monitoring logs and alerting about issues.</p>
  
  <p>What I need to be able to detect is mostly missing records:
  Say a log record was received, saying a user is about to make some sort of request. I then expect to see the log record saying the request has been made.</p>
  
  <p>If the second record was not received within X seconds from the arrival of the first, then something is wrong, and I want to alert about it.</p>
  
  <p>Any ideas how to achieve that?</p>