[tor-bugs] #2570 [Metrics]: Try harder to detect when Tonga's bridge snapshots are stale

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#2570: Try harder to detect when Tonga's bridge snapshots are stale
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  Reporter:  karsten      |              Owner:  karsten
      Type:  enhancement  |             Status:  new    
  Priority:  normal       |          Milestone:         
 Component:  Metrics      |            Version:         
  Keywords:               |             Parent:         
    Points:               |   Actualpointsdone:         
Pointsdone:               |       Actualpoints:         
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 When sanitizing bridge snapshots from Tonga, we make sure that the
 tarballs are not older than a couple of hours.  If they are, we log a
 warning, so that we know early when Tonga is broken.

 We overlooked the case when Tor crashes on Tonga, but the cronjob creates
 new tarballs with stale content every 30 minutes.  We did not detect this,
 because we have to infer the status publication time from the tarball name
 (there is no publication time in bridge network statuses).  This is how we
 did not detect that Tonga was broken for two weeks.

 We should check the descriptor publication times for plausibility.  If a
 status does not have a descriptor published in the last, say, 3 hours
 before the status was published, there's probably something wrong.  We
 should print out a warning in this case, too, and investigate the problem.

 We might also look at the last-modified times of files contained in the
 tarballs.  In theory, the time difference between writing these files and
 writing the tarball should not be higher than 1 hour.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/2570>
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