AWS Official Blog

Amazon EC2 Dedicated Instances

by Jeff Barr | on | in Amazon EC2, Amazon VPC |

We continue to listen to our customers, and we work hard to deliver the services, features, and business models based on what they tell us is most important to them. With hundreds of thousands of customers using Amazon EC2 in various ways, we are able to see trends and patterns in the requests, and to respond accordingly. Some of our customers have told us that they want more network isolation than is provided by “classic EC2.”  We met their needs with Virtual Private Cloud (VPC). Some of those customers wanted to go even further. They have asked for hardware isolation so that they can be sure that no other company is running on the same physical host.

We’re happy to oblige!

Today we are introducing a new EC2 concept the Dedicated Instance. You can now launch Dedicated Instances within a Virtual Private Cloud on single-tenant hardware. Let’s take a look at the reasons why this might be desirable, and then dive in to the specifics, including pricing.

Amazon EC2 uses a technology commonly known as virtualization to run multiple operating systems on a single physical machine. Virtualization ensures that each guest operating system receives its fair share of CPU time, memory, and I/O bandwidth to the local disk and to the network using a host operating system, sometimes known as a hypervisor. The hypervisor also isolates the guest operating systems from each other so that one guest cannot modify or otherwise interfere with another one on the same machine. We currently use a highly customized version of the Xen hypervisor. As noted in the AWS Security White Paper, we are active participants in the Xen community and track all of the latest developments.

While this logical isolation works really well for the vast majority of EC2 use cases, some of our customers have regulatory or restrictions that require physical isolation. Dedicated Instances have been introduced to address these requests.

The Specifics

Each Virtual Private Cloud (VPC) and each EC2 instance running in a VPC now has an associated tenancy attribute. Leaving the attribute set to the value “default” specifies the existing behavior: a single physical machine may run instances launched by several different AWS customers.

Setting the tenancy of a VPC to “dedicated” when the VPC is created will ensure that all instances launched in the VPC will run on single-tenant hardware. The tenancy of a VPC cannot be changed after it has been created.

You can also launch Dedicated Instances in a non-dedicated VPC by setting the instance tenancy to “dedicated” when you call RunInstances. This gives you a lot of flexibility; you can continue to use the default tenancy for most of your instances, reserving dedicated tenancy for the subset of instances that have special needs.

This is supported for all EC2 instance types with the exception of Micro, Cluster Compute, and Cluster GPU.

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). We actually go to some trouble to spread them out across several machines in order to minimize the effects of a hardware failure.

When you launch a Dedicated Instance, we can’t use the remaining “slots” on the hardware to run instances for other AWS users. Therefore, we incur an opportunity cost when you launch a single Dedicated Instance. Put another way, if you run one Dedicated Instance on a machine that can support 10 instances, 9/10ths of the potential revenue from that machine is lost to us.

In order to keep things simple (and to keep you from wasting your time trying to figure out how many instances can run on a single piece of hardware), we add a $10/hour charge whenever you have at least one Dedicated Instance running in a Region. When figured as a per-instance cost, this charge will asymptotically approach $0 (per instance) for customers that run hundreds or thousands of instances in a Region.

We also add a modest premium to the On-Demand pricing for the instance to represent the added value of being able to run it in a dedicated fashion. You can use EC2 Reserved Instances to lower your overall costs in situations where at least part of your demand for EC2 instances is predictable.

– Jeff;