Availability: it’s expensive

I was jawing today with a developer who wanted to build something a little more robust than we needed it. He didn’t do it, but he thought it would be interesting and fun (the root of another blog post one day, perhaps).

The thing is, generally cost is proportional to something like the exponent of the uptime requirement. This is why uptime is so often expressed in terms of percentage: if 9% uptime costs 1 dollar (say), then 99% costs 10 dollars, 99.9 costs 100 dollars, 99.99 costs 1000 and 99.999 costs $10,000. Now think of what an underpaid junior developer can develop in under 6 minutes, because that’s what you can build robust enough to stay up for all but five minutes per year for $10,000.

Don’t believe me? I bet your junior developer could develop something that continually writes incremental integers to the screen in six minutes. Now, how would you make that survive power failures, screen failures, how about hot-replacement of parts? Yeah, now you’re talking about $10,000.

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