The Cloud Computing concept has been invented in 2002 by Amazon, an e-business leader, which had invested in huge datacenters made of thousands of machines, something that had been dimensioned to absorb a peak of orders that their site had to sustain during Christmas holidays. However, these machines were pretty unused the rest of the year. But under-sizing their datacenters would have caused website unavailabilities during the peak, which would have been a threat to their business during the holidays, a time of the year which make up a big part of their income. So their idea has been to open these unused resources to other companies, so that they rent them on demand. Since then, Amazon invests massively in this domain and keeps expanding its datacenters and services.

Recently, other IT actors like Google and Microsoft have come into the Cloud market and now offer similar services. These Cloud Computing services, which are based at a hardware layer upon gigantic datacenters (which only these big companies can afford), and at a software layer upon modern techniques of virtualization, deliver to client companies IT resources:

• whose sizing can be changed along the time (no need anymore to buy and maintain on site big servers): it only takes a few minutes to start a new server in the Cloud (instead of several months on site!),
• which can absorb important load peaks (providers offer high performance processor and network resources),
• and whose availability is guaranteed by contract (for example, less than 5-minute unavailability per yer, or get your money back).

FlexiScale, RackSpace and GoGrid are other examples of Cloud environment providers.

The Gartner consulting institute, a reference in the field if there might be, foresees that Cloud Computing will be as influent as E-business was these past years and that it willl be massively adopted by companies by 2013.