AWS: Dedicated Host VS Dedicated Instance, why the first is more expensive than the later?

Question

I'm studying for my Associate Architect exam at AWS, and I can't find an explanation for this question. Why Dedicated Host are more expensive than Dedicated Instances? I understand the main differences between the two, it is just that in my brain it doesn't make sense.

This is my perspective: if you ask for a dedicated host, you control the entire hardware. CPUs, RAM, Sockets, etc. You can use your own license (BYOL). But if you ask for a Dedicated Instance, the hardware it is still just for you. Your AWS account is still the only one using that hardware. You have less control over it, but even though you are locking down a single piece of hardware just for your purposes.

So, why dedicated hosts are more expensive than dedicated instances, if after all, in either case, you "own" the hardware? Again, in either case, AWS won't be able to use that hardware for something else.

Answer 1

you are locking down a single piece of hardware just for your purposes.

Dedicated Instance does not work like this. Your instance runs on some dedicated hardware. Its not lockdown to you. If you stop/start instance, you can get some other hardware somewhere else. Basically, the hardware is "yours" (you are not sharing it with others) for the time your instance is running. You stop/start it, you may get different physical machine later on (maybe older, maybe newer, maybe its specs will be a bit different), and so on. So your instance is moved around on different physical servers - whichever is not occupied by others at the time.

With Dedicated Host the physical server is basically yours. It does not change, it's always the same physical machine for as long as you are paying.

Answer 2

Dedicated Host

As soon as you 'allocate' a Dedicated Host, you start paying for that whole host.

A host computer is very big. In fact, it is the size of the largest instance of the selected family, but can be divided-up into smaller instances of the same family. ("You can run any number of instances up to the core capacity associated with the host.")

Any instances that run on that Host are not charged, since you are already being billed for the Host.

That is why a Dedicated Host is more expensive than a Dedicated Instance -- the charge is for the whole host.

Dedicated Instance

"Dedicated Instances are Amazon EC2 instances that run in a virtual private cloud (VPC) on hardware that's dedicated to a single customer... Dedicated Instances may share hardware with other instances from the same AWS account that are not Dedicated Instances."

This means that no other AWS Account will run an instance on the same Host, but other instances (both dedicated and non-dedicated) from the same AWS Account might run on the same Host.

Billing is per-instance, with a cost approximately 10% more than the normal instance charge (but no extra charge if it is the largest instance in the family, since it requires the whole host anyway).