Friday 7 November 2008

Cost in the Cloud

Cost is slated as benefit number 1 in most of the cloud fanboy buzz, and they're mostly right, usage-based and CPU-time billing models do mean you don't have tons of up front capital assets to buy - but that's not the same thing as saying all you cost problems are magically solved. You should still be concerned about cost - except now you're thinking about expensive operations and excess load.

Code efficiency sometimes isn't as acute a concern on a traditional hardware platform because you have to buy all the computers you'll need to meet peak load, and keep them running even when you're not at peak. This way you usually have an amount of free capacity floating around to absorb less-than-efficient code, and of course when you're at capacity there is a natural ceiling right there anyway.

Not so in the cloud. That runaway process is no longer hidden away inside a fixed cost, it is now directly costing you, for example, 40c an hour. If that doesn't scare you, then consider it as $3504 per year - that's for once instance, how about a bigger system of 10 or 15 instances? Now you're easily besting $35K and $52K for a process that isn't adding proportionate (or at worst, any) value to your business.

Yikes. So stay on guard against rogue process, think carefully about regularly scheduled jobs, and don't create expensive operations that are triggered by cheap events (like multiple reads from multiple databases for a simple page view) if you can avoid it. When you are designing a system to run on a cloud platform, your decisions will have a significant impact on the cost of running the software.

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