There are three basic options for firms who want to use the Cloud to improve business processes, IT support and delivery; or to handle capacity and storage. First, firms may rent the cloud infrastructure and deploy their own application on top of this rented infrastructure. Second, firms may rent a service, including application software, in the cloud, which is hosted on a remote platform. The former option basically deals with outsourcing hardware and infrastructure, and the second option is focused on utilizing a package or service.
In the real world there is also a third option – hybrids. These are rarely discussed but quite practical. A hybrid cloud is where you own some part of the Cloud architecture, but integrate this controlled environment, with a cloud service, or system, which maybe be running on a 3rd party hosting infrastructure. An example is a client using cloud enabled-specialized software from one vendor, which integrates with the internal legacy systems of the client. This specialized cloud-software firm might host its application remotely using a 3rd party which provides IaaS and PaaS, such as AWS. It is transparent to the client, and the client could care less as long as the software is available and reliable. This is a rather common scenario involving:
Software as a Service Oriented architecture exemplifies the hybrid potential of mixing and matching platforms within the Cloud. There is no single 'Cloud' architecture that you must aspire to. The exact nature of what is cloud enabled, and how it is built, supported and extended and where it is hosted, all depends on budget, internal skill sets, purpose of the service or software, and cloud characteristics such as reliability, availability, fail-over and redundancy.