Cost-Aware Architectures by Werner Vogels

As engineers we are remarkably badly trained in thinking about cost. I don’t mean some big O order of magnitude cost but real dollar cost. You could given me five fault-tolerant algorithms and almost with my eyes closed I could pick the best one. But if you would then ask me what the difference would be in cost between the best and second-best when the system would start to scale I would falter.

I learned how to incorporate cost into architecture the hard way. At Amazon.com the margins are, as in most retail, razor thin and as such any fluctuation in the cost of infrastructure and systems immediately eats into the bottom line. And Amazon.com has many moving pieces, with hundreds and hundreds of internal services, so keeping control over cost, architecturally, is just plain hard. Especially in the days before we had AWS, our cloud services.

The most important concept is that, when you are growing, your cost should grow over the same dimension your revenue is coming in over. For Amazon.com that dimension is number of orders. If orders go up your cost should be allowed to rise as well. Although if you are architected well, you will be able to exploit economies of scale and your  complete story here