Sustained-use discounts drew me to Google Cloud over AWS. Given that N2 instances lowered the sustained-use discount from 30% to 20% and the E2 instances have no sustained-use discount, it seems like Google is re-thinking whether it wants to offer sustained-use discounts. It could certainly be that my expectation that long-running VMs would use less average CPU than short-running VMs is wrong, but Google isn't pricing it that way for the 1 and 3-year committed pricing. So, it doesn't seem to be the case that Google found that there was a lot of idle CPU in on-demand VMs, but not in sustained-use VMs. A 1-year committed E2 price is 30% off the 1-year committed N1 price. The weird thing is that Google is offering a ~30% discount for everything except sustained-use. I guess the question is: why would anyone running with a sustained-use discount switch from an N1 instance to an E2 instance? The blog article sounds amazing: "we've found lots of CPU you aren't using that we re-use and pass the savings on to you!" Then it seems less fun: yea, you know how you're running a web server that's idle a lot? We'll re-use all that idle CPU, but you won't get a discount.
It's leaving around 90% of the requested CPU idle. For example, a task worker that gets around 6 tasks per hour and takes a minute per task. Lots of companies are going to have workloads that, well, are less than efficient. People leaving relatively idle VMs running in a sustained way seems ideal for this kind of scheduling. That's why I find it so curious that there's no sustained-use discount for the E2 instances. If I spin up a VM to do a video encoding task and then terminate it, I'm not leaving a lot of empty CPU that can be filled by other VMs. Who is likely to have the least unused space? The people paying by the second/hour. At least to me, it seems like the people most likely to have empty space are the sustained-use people.
That means that they're leaving a lot of unused space where you can schedule other VMs. If someone is running a web server and ends up leaving you with a lot of idle CPU, that's really good for Google. What strikes me as odd is that people getting the sustained-use discount are probably the people you'd want ton E2 instances. What's the payoff for me? Paying less! Except that without sustained-use discounts, I'm not paying less. Larger instances mean that you'll be more likely to handle spikes and live-migration means that you can balance people who are actually using the CPU a lot. That observation in combination with live-migration and larger host machines, it becomes possible to over-sell CPU cores in a way that users won't notice except in tiny ways in around 1 in 100 or 1,000 occasions. From what I understand about the E2 instances, the point is that there's often a lot of idle CPU cores compared to the vCPUs that have been allocated by users.
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