Cloud hosting services provide hosting for websites on virtual servers which pull their computing resource from extensive underlying networks of physical web servers. It follows the utility model of computing in that it is available as a service rather than a product and is therefore comparable with traditional utilities such as electricity and gas. Broadly speaking the client can tap into their service as much as they need, depending on the demands of their website, and they will only pay for what they use.
It exists as an alternative to hosting websites on single servers (either dedicated or shared servers) and can be considered as an extension of the concept of clustered hosting where websites are hosted on multiple servers. With cloud hosting however, the network of servers that are used is vast and often pulled from different data centres in different locations.
Practical examples of cloud hosting can fall under both the Infrastructure as a Service (IaaS) and Platform as a Service (PaaS) classifications. Under IaaS offerings the client is simply provided with the virtualised hardware resource on which they can install their own choice of software environment before building their web application. On a PaaS service, however, the client is also provided with this software environment, for example, as a solution stack (operating system, database support, web server software, and programming support), on which they can go straight to installing and developing their web application. Businesses with complex IT infrastructures and experienced IT professionals may wish to opt for the more customisable IaaS model but others may prefer the ease of a PaaS option.
A development of the concept of cloud hosting for enterprise customers is the Virtual Data Centre (VDC). This employs a virtualised network of servers in the cloud which can be used to host all of a business's IT operations including its websites.