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Zero Downtime? WTF!

When someone says that they want zero downtime; what is it that they really want? An absolute 100% zero downtime is absolutely impossible unless the downstate is the upstate or you live in Bizaro World. Zero Downtime should cover:

  • facilities (the building)
  • network
  • power
  • servers
  • services (database; DNS; NTP; web servers, etc...)
  • applications (userspace applications or REST services)
  • monitoring tools
  • support staff
  • versions, versions, versions...
What most sales people actually mean is completely different.
  • no perceived change in service by any of the end-users
What a systems manager actually means is completely different.
  • database schema
  • database stored procedures
  • application binding to the database - in particular strong binding through shared secrets
  • rolling service availability
What most managers forget:
  • Zero downtime is hard as evidenced by modern H.A. solutions
  • comes with a monster price tag
  • The recovery model is based on tight coupling of components
  • systems are typically master->slave with one-way artifact promotion
  • effective strategizing requires very detailed specific domain knowledge
  • ...
**Clearly perception is king.

** previously I wrote about hot-plugging code in Erlang. It's the worst thing you can do in a credit card, financial or any system with a high transaction consistency requirement.


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