The real question to me is: why would anyone fund doing this in EC2?

Here's the quick math on cost per gflop, including all network and datacenter costs:

  Mac Pro: $5/gflop
  EC2 g2.xlarge: $21.19/gflop

Not sure where you got ec2 out of my comment.

I also think you need to redo your math on the price per gflop for a Mac pro, ypou seem to be at least half the price of my back of the envelope work. Unless you have some crazy good supplier.

Exposing more detail behind this math is unfortunately not something that I'm ready to do, but I'm pretty comfortable with it in broad strokes. EC2 really is that much more expensive, when you factor in things like network bandwidth.

As I noted elsewhere, I mention EC2 because all of our (funded) competitors run there. We can split hairs over whether I could save 10% on Linux systems vs Mac systems, but the elephant in the room are all of the companies trying to make this sort of service work in EC2. You can't do it, and make money at the same time. Even if you can make money at small scale, you will eventually be crushed by your own success.

My overriding goal for imgix's datacenter strategy (and elsewhere in the company) is to build for success. To do that, we have to get the economies of scale right. I believe we have done so.

The choice isn't between a Mac Pro and EC2. You can rack up x86 boxes chock full of GPUs far more easily than Mac Pros.

I mention it because AFAIK, all of imgix's direct competitors run in EC2.

How long will it take to amortize the costs of the hardware based on EC2 g2.xlarge savings?

Not certain if I understand your question, but I'll take a shot at answering:

I expect a useful life span for any datacenter equipment of 3 years. A Mac Pros list price is about $4000. We pay less but I'll use public figures throughout. Using equipment leasing, I can pay that $4000 over the 3 year period, with let's say a 5% interest rate and no residual value (to keep this simple). So over 3 years, I spend $4315 in total per machine to get 2200 gflop/s.

Over 3 years with EC2, a g2.xlarge is $7410 up front (to secure a 57% discount) for 2300 gflop/s.

So I can pay over time, save $3100 over a 3 year period, and probably still resell the Mac Pro for $500 at the end of its life span. That's pretty compelling math to me. There are costs involved with building and operating a datacenter, and that evens things out a bit. What really kills EC2 though is the network bandwidth costs. It is just insane.

It'll be REAL f'in expensive in EC2, that's for sure.