[Xylakant]

This may be swayed by the fact that you might have a task that can be run in parallel on multiple machines and then finish in an hour, so that you can then move on. Buying or renting enough capacity and then leaving idle for the remaining time is not an option, but with AWS you can easily spin up 100 instances for an hour and do the computational worth for 4 days of a single machine, then shut them down at no extra cost.

[vonmoltke]

That is the use case that AWS is best for. That is not the use case covered in the article, though. The use case being discussed is that for a cluster of always-on machines with a fairly consistent load. If you have a minimum baseline load on your servers, fulfilling that from AWS, or Azure, or similar services doesn't make financial sense. Colocated (if you don't mind dealing with the hardware) or leased (if you do mind) servers for your baseline load combined with cloud machines for load spikes makes the most sense.