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From Andrew Purtell <apurt...@apache.org>
Subject Re: Performance of EC2
Date Thu, 28 Jan 2010 08:44:43 GMT
> > But what I don't understand is this... if I *reserve* an instance then I
> > wouldn't be sharing its CPU with anyone, right?  The blog seems to indicate
> > otherwise.

No, that is not how EC2 and similar cloud infrastructure platforms work. You are
given a virtual machine. The hypervisor multiplexes many virtual machines on a
single physical server. The instance types purport to guarantee a certain level
of performance measured in virtual CPU units. The EC2 website describes in detail
how Amazon defines a virtual CPU unit. 

> > (Occasionally my instances fail
> > on startup or die in the middle for no apparent reason, and I used to think
> > I was doing something dumb!)

That is also a misunderstanding of how to use cloud infrastructure. No single
instance is reliable. The platform is a commodity, cheap, with basic usability.
Durable services are built on top of these building blocks with service
architecture that does not rely on the stability of any single instance. 

   - Andy


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