There are a few problems with this approach, though. One is that it doesn’t take complete advantage of modern server’s processing power. Most servers use only a small fraction of their overall processing capabilities. Another problem is that as a computer network gets larger and more complex, the servers begin to take up a lot of physical space. A data center might become overcrowded with racks of servers consuming a lot of power and generating heat. Last but not the least, dedicating individual machines for each application certainly increases the infrastructure and hardware costs of any organization.

Server virtualization attempts to address all of the above issues. By using specially designed software, an administrator can convert one physical server into multiple virtual machines. Each virtual server acts like a unique physical device, capable of running its own operating system (OS).

There are three ways to create virtual servers: full virtualization, para-virtualization and OS-level virtualization. They all share a few common traits. The physical server is called the host. The virtual servers are called guests. The virtual servers behave like physical machines. Each system uses a different approach to allocate physical server resources to virtual server needs.

Full virtualization uses a special kind of software called a hypervisor. The hypervisor interacts directly with the physical server’s CPU and disk space. It serves as a platform for the virtual servers’ operating systems. The hypervisor keeps each virtual server completely independent and unaware of the other virtual servers running on the physical machine. Each guest server runs on its own OS. You can even have one guest running on Linux and another on Windows. The hypervisor monitors the physical server’s resources. As virtual servers run applications, the hypervisor relays resources from the physical machine to the appropriate virtual server. Hypervisors have their own processing needs, which means that the physical server must reserve some processing power and resources to run the hypervisor application. This can impact overall server performance and slow down applications. VMware and Microsoft Virtual Server both use the full virtualization model.

The para-virtualization approach is a little different. Unlike the full virtualization technique, the guest servers in a para-virtualization system are aware of one another. A para-virtualization hypervisor doesn’t need as much processing power to manage the guest operating systems, because each OS is already aware of the demands the other operating systems are placing on the physical server. The entire system works together as a cohesive unit. Xen and UML both use the para-virtualization model.

An OS-level virtualization approach doesn’t use a hypervisor at all. Instead, the virtualization capability is part of the host OS, which performs all the functions of a fully virtualized hypervisor. The biggest limitation of this approach is that all the guest servers must run the same OS. Each virtual server remains independent from all the others, but you can’t mix and match operating systems among them. Because all the guest operating systems must be the same, this is called a homogeneous environment.Virtuozzo and Solaris Zones both use OS-level virtualization.

In my previous post, I pointed to a simple non-technical introduction to cloud computing. In this article I give a more technical perspective to it.

What is Cloud Computing?

 “Cloud computing is Internet (“cloud”) based development and use of computer technology, whereby dynamically scalable virtualized resources are provided as a service over the Internet. Users need not have knowledge of, expertise in, or control over the technology infrastructure ‘in the cloud’ that supports them.” Wikipedia

“Cloud computing is emerging at the convergence of three major trends – service orientation, virtualization, and standardization of computing through the Internet. Users will need to understand the cloud options and providers available to them. Vendors will need to evolve their platforms to be cloud-capable, and evolve their business models to maintain their competitive advantage.” Gartner

Google Trend for Cloud Computing

Cloud computing emerged as a promising technology in late 2007. Since its emergence, there have been several projects supporting this concept in industry and academia. Some examples (in no specific order) are: Amazon Elastic Compute Cloud (EC2), Amazon Simple Storage Service (S3), ElasticDrive, Enomaly, IBM Blue Cloud, Global Cloud Computing Testbed, Google Docs, Adobe Buzzword, and Google App Engine.

Services of Cloud Computing

Conceptually, cloud computing offers a high level of abstraction to its users. It provides some level of service to its users without revealing any details regarding hardware, software, hosting, deployment, and scalability. The services offered in a cloud can be categorized as:

SaaS: Software as a Service

Software or applications are hosted on the cloud and are offered to users from a Web Interface (browser). Users can avail these services without having to worry about the application internals or the infrastructure used to deploy them. Examples of SaaS include Facebook and Gmail. This concept can be further enhanced with pay as you go where clients can pay for the quality or quantity of such services used. Examples of this model are SalesForce.com and WebEx.

DaaS: Data as a Service

Data in various formats and multiple sources can be seamlessly deployed on the cloud. Users generate and access this data in the same manner they would on their local machines, just that it is eventually stored on the cloud. Examples of this category of service include Amazon Simple Storage Service (S3), Google Docs, and Adobe Buzzword. One can argue that DaaS is a specialized case of SaaS where the software particularly caters to manipulation of data. However, considering its usage and scale I personally feel it justifies its own category.

IaaS: Infrastructure as a Service

Infrastructure encompasses some sort of compute or execution service offered by the cloud. It is enabled by the virtualization technology that allows partitioning and sharing of infrastructure resources and scaling them up or down as per client requirements. Examples of IaaS include Amazon Elastic Compute Cloud (EC2).

Paas: Platform as a Service

A cloud platform service offers an application development environment to its users enabling them to develop cloud applications sans the low-level details of the cloud. It is analogous to a programming language that shields the programmers from technical details of operating system and underlying hardware. An example of PaaS would be Google App Engine and Microsoft Azure.

Characteristics of Cloud Computing

Instant Availability: Without any software or hardware installation users can avail the services out-of-the-box from the cloud

Elastic: Based on user requirements and budget cloud services (SaaS, DaaS, IaaS, PaaS) can be scaled up or down without affecting the service functionality

Pay/Use as you Go: By virtue of its elasticity and virtualization, users can utilize cloud environments and pay for exactly what they need/use

Quality of Service: With experts managing the cloud platforms (and of course charging for it), users can be guaranteed pre-defined quality of services.

Technologies in Cloud Computing  

Cloud computing is not a technology by itself. Rather, it is facilitated by the aggregation of several disparate technologies and initiatives.

Web 2.0: The advancements in the way we use Internet has promoted the concepts of cloud computing. With the advent of AJAX and related technologies, rich user interfaces are no longer restricted to local PC-based installations.

Virtualization: New developments in the virtualization technologies (Xen and VMware) have facilitated the concepts in infrastructure sharing and sandboxing without affecting its performance and scalability.

Web Services: The standardization in Web Services world has certainly helped in the proliferation of the service concept being adopted by industry. Not only can these services be used in isolation but can also be embedded by organizations into their SOA architecture.

To summarize, cloud computing environments have demonstrated an innovative model of service and resource sharing. They have also been accompanied by a lot of buzz and hype from the industry. However, it is still in its initial stages and needs to go through the standardization phase before it can be adopted en masse via cross compatible clouds.  

www.youtube.com/watch?v=QJncFirhjPg