Virtualization Technology

I have been hearing about this term called “Virtualization” for some time now, from the media and at several technical events. Let’s try to understand what does it really mean? I would like to start of with this definition on virtualization given in Wikipedia.

In computing, virtualization is the process of presenting a logical grouping or subset of computing resources so that they can be accessed in ways that give benefits over the original configuration. This new virtual view of the resources is not restricted by the implementation, geographic location or the physical configuration of underlying resources. Commonly virtualized resources include computing power and data storage. A new trend in virtualization is the concept of a virtualization engine which gives an overall holistic view of the entire network infrastructure by using the aggregation technique. Another popular kind of virtualization, and currently very referred to in the media, is the hardware virtualization for running more than one operating system at the same time, via nanokernels or Hardware Abstraction Layers, such as Xen.

The following extract is from an IBM whitepaper on Virtualization. The extract talks about the need for virtualization and the meaning of virtualization:

Tight budgets, limited resources and short deadlines are a fact of life. That may be the reason why insightful IT analysts have recommended virtualization technology as an effective method to improve utilization rates, increase server flexibility and reduce IT spending. Simply put, virtualization technology is a way to pool IT resources while masking the physical attributes and boundaries of the resources from users of the resources, which can result in providing customers with the important advantages listed above. Although virtualization is not a new technology, it is receiving a lot of attention. Much of this renewed interest can be attributed to non-mainframe environments. Other platforms have recently realized the benefits of virtualization and are starting to develop and deploy forms of mainframe-inspired partitioning and virtualization to enhance their environments and remain competitive.

WorkflowWebRequestContext removed from WWF Beta 2.2

This came as a surprise to me. In fact, I was using WWF Beta 2 in my application, where my web service was triggering the workflow. In a web scenario, this class was really useful in ensuring that there was only one workflow runtime instance per app domain, which is otherwise slightly difficult to ensure. Last week, I came to know that this class has been removed in Beta 2.2. I decided to check out why Microsoft WWF team had decided to remove this type from the library.

When I started searching for some information on this, I hit upon this document, which talks about the Microsoft® Visual Studio® 2005 Extensions for Windows® Workflow Foundation Beta 2 to Beta 2.2 Key Changes. What this document says is that:

The WorkflowWebRequestContext type will be removed to protect the WorkflowRuntime being accessed by all of the workflow instances. The following will be added to WorkflowWebService: protected WorkflowRuntime WorkflowRuntime { get; }

 

One way to ensure that only one workflow runtime instance is present per app domain; is to instantiate the workflow runtime in the Global.asax application start event and use this instance across the application.

I have not personally used the WorkflowWebService class, but it represents the base class for all workflow Web services. So in my case I will have to inherit my web service class from WorkflowWebService class and then use the newly added protected WorkflowRuntime property to get the current instance of the workflow runtime. The WorkflowWebService class actually inherits from System.Web.Services.WebService class.