The reliability pillar of the AWS Well-Architected Framework [pdf]

The section about calculating the availability of hard and redundant dependencies ignores the fact that systems often fail in tandem. For e.g. you might have a primary and secondary database in different AZs, each with 99.9% availability. This gives read operations a hypothetical uptime of 6-9s. But hidden SPOFs like operator error, VM infra failing, load balancer or other networking outages can make the 0.01% failure time overlap, blowing away your 6-9s dependency guarantee.

This is total submarine marketing by AWS. Im sure some very smart people with good intentions at AWS produced this, but the fact is they&#x27;re not an independent academic providing objectively &quot;the best&quot; practices, they&#x27;re a company trying to sell you something. They probably in full belief in their own abilities believe the AWS way of doing things is best, but frankly, I know as much as you do, or at least if you want to win me over you need to comprehensively prove it, not just preach from the hill.<p>TL:DR stop telling me you&#x27;re doing better architectures in the same of selling me something

&gt; &quot;... For example, if a system makes use of two independent components, each with an availability of 99.9%, the resulting system availability is &gt;99.999% ... &quot;<p>This does not seem correct.

Interesting that security is 1 of 5 pillars and hardly gets a mention in this paper. Who wrote this and why?

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