Cloud Computing Architecture

Cloud Computing Explained
-A Biswas

Cloud Computing is the the catch-phrase of the current decade, that echoes in the corridors of lT Head quarters of different organizations. If you are part of any IT organization, you may frequently hear about some upcoming projects on moving bulk of IT services to cloud computing platforms.

Even to a seasoned IT guy, it may initially sound fuzzy. In very simple terms, the cloud is a clichéd metaphor for the internet. It can be very narrowly described as a glorified version of utility computing, basically composed of a bunch of virtual servers on the internet. Some define it too broadly, saying that all the 'services' you consume outside the horizon of your firewall are "in the cloud".
To understand the basics of cloud computing, please watch the video.




Let us move to a more professional and authentic definition provided by NIST (National Institute of Standards and Technology). Cloud computing is a model for enabling 'ubiquitous, convenient, on-demand' network access to a shared pool of configurable computing resources, that can be rapidly provisioned and released with minimal management effort, or service provider interaction. Now, it goes without emphasis that the cloud computing concepts are rooted in the service-oriented IT philosophy, wherein the entire service oriented framework is a way of envisioning IT in terms of services, service-based development and the outcomes of services. According to NIST, Cloud computing encompasses three service models - cloud infrastructure as service, cloud platform as service and cloud software as service. Cloud computing goes to extent of commoditization of the IT services, where you trade and consume IT services based on some pay-per use model, just like gas and electricity. Cloud computing is an extension of a paradigm, wherein the capabilities of business applications are exposed as 'services' that can be accessed over a network. This model promises some unique advantages. First, it is possible to eliminate the setup and maintenance cost of elaborate infrastructure and there is no need for 'in-house' provisioning. The next plus point is the capability of global reach and it is not uncommon now-a-days to access applications or databases online independently without reference to the underlying hosting infrastructure.

The Cloud model of NIST is characterized by :(i) Five essential characteristics (ii) Three service models and (iii) Four deployment models.
Let us first understand what are these essential characteristics. As emphasized by NIST, the manadatory and primal characteristics of Cloud architecture are - (a) on-demand self-service (b) broad network access (c) resource pooling (d) rapid elasticity and (e) service measurability.
Three service models propagated by NIST are : cloud infrastructure as service, cloud platform as service and cloud software as service. The service models in Cloud are derived from the principles of SOA, where Cloud computing architecture is discussed in terms of creation, delivery, distribution and consumption of IT services. Earlier we talked about software as services, here entire IT functionalities and their outcomes are exposed as services.
To explain the Could Deployment models, let me refer to IBM's Reference Architecture document on cloud computing. The four models of cloud are: Private, Community, Public and Hybrid.We call it 'Private' when the scope of the architecture and solution bandwidth remain within the organization boundaries.If it scopes beyond the organizational fence, it is nomanclatured as 'Public'. The 'Hybrid Model' is a natural mix or combination of both types.