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Comment by ericz | Hacker News Reader

I don't see how this makes sense for Amazon.

The $10/hr charge seems to be a flat rate no matter how many dedicated instances you have in the region. Thus I can start 10000 "small" instances and pay pennies per hour + $10/10000. Surely a small instance does not cover the cost of an entire physical machine.

This seems like an economical way to DoS EC2

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The crucial point is that you can still have multiple VPS's on a single machine, but you're guaranteed they'll all be yours. That is, the only difference with the dedicated instances is that there won't be an instance of someone else running on a machine you're also using.

I think most people wouldn't want to enable this unless you're required to; chances are that when one instance needs all the resources, the others are busy too, and then suddenly you have all your instances competing for resources on the same machine.

I think you missed this part: "launching a set of instances with dedicated tenancy does not in any way guarantee that they'll share the same hardware (they might, but you have no control over it)". In other words, when launching many small/medium instances they will make sure to stuff them onto only a few physical machines. So dedicated tenancy does not mean no virtualization - it just means that you don't share hardware with other users. So this is really just a way to accommodate whatever privacy policies that might require such thing.

> Surely a small instance does not cover the cost of an entire physical machine.

Who said you'd get a machine per instance? All they're promising is that no one else's instances will be on the servers hosting your instances.

I'm pretty sure the $10/hr ensures no-one _else's_ VMs run on the hardware your VM is running on. If you spin up 10 small instances, I think they'd happily put them all on the same hardware, just like that might have done anyway, and pocket the $10/hr for no cost to Amazon (except the minor administrative cost associated with getting that all right).

Sounds like this might reduce redundancy - if all your instances tend to be on the same machine, a single failure could take them all out...

It doesn't work like that. There's some intelligence built in to the instance placement algorithm to guard against this.

The $10/hour charge is to make up for the fractional machine you are wasting. That doesn't change as you add more instances. There is always just one fractional machine being wasted.

They only let you launch 20 EC2 instances unless you request an increase[1]. I assume you need a damn good use case before they're up your limit to 10,000.

[1] - http://aws.amazon.com/contact-us/ec2-request/

I think it is more of a credit check than a use case you need.

Ya, it's just this. And also a check against spam farms.

Even if you started up 10,000 Dedicate Instances you would not tie up 10,000 physical machines. A Dedicated Instance won't share hardware with another customer's VM but it could share hardware with your other VMs. It would probably be beneficial to you if they did, as the post says:

"It is important to note that launching a set of instances with dedicated tenancy does not in any way guarantee that they'll share the same hardware (they might, but you have no control over it)."

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