Byzantine or Baroque
Lets talk gardens.
In the Byzantine period, 1000 years 330-1453 AD, gardens were not open with grand vistas. Horticultural interests, cost considerations and security concerns fomented walled gardens which could be easily overseen. To provide a sense of openness, faux vistas were painted on the walls.
Baroque was the 17th century and gardens in relatively stable France were immense expanses of interconnected garden spaces. Each space, walked and explored, provided its own experience but the garden was meant to be seen as a cohesive whole. The control of nature theme expressed itself as innumerable water features which were so taxing on the infrastructure that many gardens could only run for short periods of time.
We use the term cloud architecture to mean the three prevalent architectures involving cloud services: private cloud, public cloud and hybrid cloud.
A private cloud is defined as the use of cloud services within the perimeter of the Enterprise. This model is generally the starting point for many Enterprises as they try to reduce data center costs through the use of virtualized infrastructure. In this sense, the private cloud model is the safest model for an Enterprise to deploy as it does not incur the lack of control, security, reliability and ownership seen in the hybrid cloud or external public cloud architectures. On the flipside, the private cloud model also lacks the respective benefits such as the reduction in capital or operational costs.
The next architecture, the hybrid cloud is the more common example of an Enterprise using an external cloud service in a targeted manner for a specific business need. This model is hybrid because core business services are left in the Enterprise perimeter and some set of cloud services are selectively used for achieving specific business goals. This usage can be understood as having two drivers: The first driver typically called cloud bursting is the use of a cloud service for a short-lived project such as a rapid prototyping, ad hoc batch processing, demos and proof-of-concept work. A practical example of this would be the instantiation of an Amazon EC2 cloud instances for handling additional peak traffic during a busy season. The important point here is that this use of the public cloud is short-lived and relatively disconnected from the rest of the Enterprise. The second driver is the migration of important, but not core business critical services to the cloud. The typical example here is the use of a platform such as salesforce.com for customer relationship management. While we can all agree that CRM is important part of any business, it is a utility service and not a core competitive weapon for the business. In fact, the existence of these utility services on the cloud serves to bring all business to the same level, blunting the competitive edge.
The third architecture, called the public cloud can be understood with two variations, a strong assumption and weak assumption. The strong assumption is really a thought experiment that states the possibility of offloading all Enterprise services to some external cloud provider and simultaneously reaping the time-to-market, capital, and maintenance costs. This scenario would involve the total offloading of all information systems to a set of trusted cloud providers. In contrast to the hybrid cloud definition previously given, the external public cloud architecture is saying that all information systems in the Enterprise, including supply-chain, business intelligence systems, CRM , order tracking, purchasing, billing and accounting can in principle be moved to the external cloud. While the thought experiment rings true, understood through a technology lens, it is arguable whether or not a business can survive with all of its information systems living in the cloud – there may be competitive reasons why it needs direct ownership of core information systems and infrastructure. For example, it may need to make real-time changes to its information systems not possible if the same systems were split across a multitude of external providers. This leads to the weak assumption for the external public cloud which states that an Enterprise will offload all that it reasonably can to the cloud but maintain some business critical information systems on premise. This architecture can be thought of as a re-statement of the hybrid cloud, but with more services offloaded to external providers.
Next, illustrating the architectures.