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2. STATE OF THE ART AND RELATED WORK 2.1. Virtual Appliances 2.1.1 Virtualization Virtual Appliance JeOS Virtualization Layer Physical Hardware Figure 2.1: Virtual appliance Virtualization is a very broad term and refers to something which does not exist physically but appears to exist. Think of it in the context of virtual reality. With virtual memory, for example, computer software gains access to more memory than is physically installed, via the background swapping of data to disk storage. Similarly, virtualization techniques can be applied to other IT infrastructure layers such as networks, storage, laptop or server hardware, operating systems and applications. The concept of platform virtualization refers to the technique for hiding the physical char- acteristics of computing resources from the way in which other systems, applications or end users interact with those resources. In other words, virtualization allows multiple logical computing units to run on a single physical computing unit, like in the Figure 2.2. This is done with the aid of a software layer (alias virtualization layer, virtualization manager, virtual machine monitor or hypervisor) which provides the illusion of a “real” machine to multiple instances of “virtual machines”. Virtualization Layer Computational Unit Figure 2.2: Physical unit running four VMs 12
2. STATE OF THE ART AND RELATED WORK 2.1. Virtual Appliances The virtualization concept goes back to the 1960s when corporate mainframes were in a severe underutilization state [oV08]. By then, some IBM research personnel were working on the CP-40 OS designed to run on the System/360 time-sharing system. It was the first OS to completely virtualize a system (namely System/360) so that other S/360 OSes could be tested and executed. This system paved the way for virtualization as known nowadays and concepts pioneered by CP-40 are still actual, like the case where an abstraction layer catches traps and simulates them. Curiously, CP-40 is still supported by IBM mainframes (System z10). Presently, mainframes came to suffer from the same underutilization problem and so virtualization is en vogue once again. 2.1.2 Motivation Nowadays, deployment via download or DVD defines the typical software distribution model. Despite its simplicity, this model features limitations such as deployment and configuration complexity. Other flaws that might be pointed are the huge number of application versions to maintain, which leads to IT resources draining; having to cope with a myriad of hardware plat- forms, which leads to intensive time-consuming testings; Independent Service Vendors (ISVs) might see their revenues decreased since if the customer is content with the product, he will only upgrade when a groundbreaking feature comes out; and so forth. As a response to these challenges, some alternative deployment models arose. Such is the case of Software as a Service (SaaS), hardware appliances and virtual appliances. Software as a Service (SaaS) This approach consists on providing a service by hosting a software application that customers over the Internet can use. In this way, the need for install and configure on the customer’s computer is eliminated, so problems as software maintenance and support are no longer customer’s responsibility but software vendor. The revenue becomes different: customers pay when they want to use the service, rather than having a single expense when purchasing the application. However, this will turn the application vendor into a service provider that has to maintain its infrastructure. Also, given the variety of existing open-source solutions and the inexpensive hardware, it appeals economically to the customer to keep the application running under its control. Hardware Appliances Another approach to software distribution is the creation of hardware appliances bundling the application with hardware capable of running it. The customer just needs to plug in the appliance and turn it on. This approach also clears the need for the customer to install and configure the application, but this forces the application vendor to enter a different market, the hardware market. 13
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Bibliography [Ama09] Amazon. Amazon
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BIBLIOGRAPHY [Sol09a] Evolve Space
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Dissertaç ˜ao de Mestrado Mestrado em Engenharia Informática Jo ...

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