Client-Server Virtualization

Client-Server architecture lends itself to the virtualization of applications. It stands poised to enjoy all the benefits. Application virtualization abstracts the application and removes it to a centralized database. However, the local experience of the end user is the same. Application virtualization addresses the limitations of client-server technology. For example, in traditional client-server technology, client programs must be installed on each user system, therefore client applications must be duplicated for each user.

This can affect performance if bandwidth is limited or connections are unstable. If the client program is virtualized, it is running on a server in a data center instead of taking up space and power on the user system. The experience is the same for the user and he/she can access all the features of the client program. Consolidating it in a central location, however, yields obvious benefits in application delivery. For example, initial application deployment, updates, and patches can occur in a matter of minutes or hours. This is in direct contrast to the lengthy investment of manpower that was previous required to make to ensure enterprise-wide application accessibility. Consolidating applications in data center and making the client virtual also improves security, since application files are not dispersed through an organization, but can be monitored and maintained easily from their central location. Performance and user response times improve because delivery is streamlined, requiring less bandwidth, which also reduces costs. Client virtualization also increases mobility and flexibility.

For example, since the client runs from a central server it can be accessed from other systems besides the user’s PC. Any device that can gain access to the data center can have access to the application and its services. This means business continuity improves because people can work from anywhere, such as when traveling.

Server virtualization masks the physical realities of servers. For example, the identity and number of servers is concealed, as are other processors and operating systems. Software application partitions a single physical server into several isolated environments. These are also known as emulations, partitions, containers, instances, or guests. Virtual servers are organized according to the guest-host model. Guests use virtual hardware on the server, so they can function without modification regardless of the actual server’s operating systems. There are three primary types of virtual servers: the virtual machine model, the paravirtual machine, and the virtualization of the operating system (OS) layer. The virtual machine model was described above in the partitioning discussion. However, this type of virutalization requires a few more elements.

For example, virtual machines use hypervisors to communicate and execute any processing demands made by the virtual machine. Hypervisors are also called virtual managers or VMMs (Virtual Machine Managers). They allow different operating systems to share hardware and manage executed coded that demands more privileges from the central processing unit. The paravirtual machine model (PVM) also uses the guest/host model, including a virtual machine monitor. However, in the PVM the VMM actually modifies the host’s operating system through porting.

Portability allows a computer program to function in operating systems other than the one that created without requiring additional networking. Porting, the verb form of portability performs any work demanded by the program to exist in the different environment. It allows PVMs to use resources as needed and run multiple operating systems simultaneously.

Operating system (OS) virtualization varies the guest-host paradigm. In this model, the host runs a single OS kernel as the core and exports OS functions to guests. Kernels contain the basic functions of operating systems. In this configuration, guests must use the same operating system as the host, but the distribution of services may be varied according to guest demands. This creative distribution removes the need for system calls between layers, thereby reducing CPU processing usage. Each partition must remain isolated so that any failure in one does not affect the entire system. Common code binaries and libraries exist on the same machine and can be shared. This allows OS virtual servers to host a multitude of guests (thousands) simultaneously.

Virtualization Products

Virtuozzo and Solaris Zones both provide products that support OS virtualization. XEN and UML offer PVM virtualization. VMware and Microsoft’s Virtual Server both provide the technology, such as hypervisors, to support VMs.

For small to medium businesses the top virtualization products include the following: Acronis’ FullCircle, Parallel’s Workstation for Windows and Linux, VMware’s Infratstructure 3 (Starter Version), XenSource’s XenServer for Windows.

Intel uses virtual technology in an Embedded IT (EIT) that supports client provisioning, manageability, isolation, and recovery. IBM’s Virtual Client Solution cuts costs through centralization while retaining user’s control of their computing environment.

First Page: Virtualization and Client-Server Technology