Besides the split into SaaS, PaaS, and IaaS, cloud computing has divided along another dimension. Though initially cloud referred to software accessed over the public Internet/Web, enterprises quickly realized that environments could be set up internally that have the essential cloud characteristics enumerated above: network-based self-service deployment and elastic capacity. Such “on-premise” or “internal” clouds have come to be referred to as “private cloud”. Private cloud platform does entail some up-front investment in hardware and set-up as well as ongoing administration on the part of the enterprise.
Because integration flexibility and control over quality of service and security are high priority for larger enterprises, and because such enterprises likely have the financial resources to optimize for costs over time rather than up-front costs, many enterprises will naturally gravitate towards the private variant in their adoption of cloud computing. An additional aspect strengthens this bias: adopting private cloud practices will be a small change for many enterprises.
IT departments have in many cases already gone significantly down the path of consolidating infrastructure and setting up shared services, and enabling cloud’s self service and automated dynamic capacity will often be a relatively small incremental step. This is in contrast to adoption of a public cloud offering, which will dramatically change how departmental users obtain application support.
In setting up a private cloud, the natural organizational structure comprises a central IT function that sets up and manages the cloud itself and various functional or product departments across the enterprise that are “customers” of the cloud. For an private cloud, the most appropriate type is PaaS. If the central IT function were to set up an offering at the IaaS level, the departmental users would need too much IT expertise themselves in order to make use of the cloud, thus defeating the economies of centralizing the IT function in the first place.
At the other end of the spectrum, an internal SaaS offering would not likely make sense in very many cases because departments wouldn’t have the flexibility to create the specific functionality they require—there are very few applications that would fulfill a majority of functional needs across multiple departments. The platform level of PaaS is the right balance between flexibility and ease of use for the departmental cloud customers.
Private cloud platform as a service