Software as a Service

The best interpretation for the SaaS model is on-demand software. The user need only configure the software to use and interact with it. The draw to SaaS is that there's no need to learn how to deploy the software to get it working in a larger stack, and generally the charges are per-usage-hour. In the case of AWS, much of the maintenance burden is also removed. 

The AWS suite is both impressive and unique in that it doesn't fall under any one of the cloud service models we described previously. Until AWS made its name, the need to virtualize an entire environment or stack was usually not an easy task and required integration of different providers offerings, each solving a specific part of the deployment puzzle. The cost of using many different providers to create a virtual stack might not be cheaper than the initial hardware cost for moving equipment into a data center. Besides the cost of the providers themselves, having multiple providers also created the problem of scaling in one area and notifying another of the changes. While making applications more resilient and scalable, this Frankenstein method usually did not simplify the problem as a whole.