service complexity and traffic levels
introduction
The two big factors that influence how many computers you need and how much bandwidth you must rent are service complexity and traffic levels.
what it is
Service complexity is the number of moving parts in the virtual machine you build. A brochure with images has very few. It is a simple service. A family image gallery is a more complex service. The web server may have to arrange image files into photo albums.
A medium-complexity service like an online shop needs a computer connected to the Internet to provide the storefront and a couple more computers running behind the scenes to calculate stock levels and process payments. A high complexity service like a top social networking site may use thousands of computers at busy periods. Cloud computing and cloud storage are ideal for these top sites, because the computers are all virtual and can be deleted during quiet times.
Traffic level is the number of visits and the amount of data uploaded and downloaded. A family picture album has low traffic: the audience is limited to dozens of people. A simple service with a big audience, such as a government announcement page visited by half the country's population, is low complexity and high traffic.
The Glastonbury Festival ticket web site is visited by hundreds of thousands of people at the same time, all desperate to buy one of the 175,000 tickets on offer. Tickets sell out within hours. The web site has to store customer details, check stock, check credit cards with a bank and so on. This site is high complexity and high traffic, but only for a few hours.
The family album can be handled by single IBM PC and a puny Internet connection with a 1MB upload. The government announcement page needs several computers to hand out the page to many thousands of people at the same time. It also needs much higher bandwidth.
If the family in the example above decide to sell the photos over the Internet rather than giving them away, the service becomes more complicated because it needs to be able to register customers and take payments. Its need for computing power grows. If the family become famous then the service becomes busier. The higher the traffic the more computing power is required. The family have the choice of either buying one big expensive computer or buying a couple of cheap ones to handle the increased computing workload. Most companies go for the cheaper option: multiple computers working together. After all, this year's cheap computer was last year's top of the range flagship.
