Scaling on Amazon EC2

Question

Hi, I have several newbie questions about EC2, thanks for your attention,

1) why EC2 instances come with specific memory/storage quotas? In the cloud environment, can't we just request the amount of memory/storage as we require, and the amazon infrastructure take care of the allocation? I understand an pre-determined allocation of memory/storage is required to setup a VM image, however, is this indeed necessary ? In Google app engine, I don't see any limit on the memory, and the storage is charged in a pay-as-you-go manner.

2) Related to the first. If amazon allows instances created with a dynamic memory/storage quote, do we still need to create multiple instances and take care of load balancing, e.g. Or, we can just create a powerful instance, and leave other scaling issues to Amazon.

3) The performance of EC2 instance, do you have experience to tell how it compares to a physical machine with similar configuration (memory/CPU)

Answer 1

why EC2 instances come with specific memory/storage quotas? In the cloud environment, can't we just request the amount of memory/storage as we require, and the amazon infrastructure take care of the allocation?

Because EC2 emulates individual machines that you can control while you have no control over these "computers" on GAE. You cannot do things like use files on GAE.

Related to the first. If amazon allows instances created with a dynamic memory/storage quote, do we still need to create multiple instances and take care of load balancing, e.g. Or, we can just create a powerful instance, and leave other scaling issues to Amazon.

You will usually need to do this by yourself. EC2 provides on demand virtual "computers".

The performance of EC2 instance, do you have experience to tell how it compares to a physical machine with similar configuration (memory/CPU)

"One EC2 Compute Unit equals 1.0-1.2 GHz 2007 Opteron or 2007 Xeon processor."

Answer 2

Fundamentally it's because Amazon's infrastructure is based on the Xen virtualization platform, and Xen does not support dynamic reallocation of resources between VM's.

VMWare has announced support for that type of reallocation. It will be interesting to see how Amazon reacts.