CompTIA Cloud+ Study Guide. Ben Piper
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СКАЧАТЬ Virtualization

      Machine virtualization—also called server virtualization—involves abstracting the resources of a single physical server into multiple virtual machines (VMs). Essentially, a VM is a software-emulated computer consisting of virtual CPUs (vCPUs), memory, storage, and networking. Like a real computer, a VM runs an operating system (OS) called a guest OS. The software that creates virtual machines and performs this abstraction is called a hypervisor. The hypervisor also defines the properties of a VM, including the following:

       The number of virtual CPUs

       The amount of random access memory (RAM)

       The type and amount of storage

       Virtual network interfaces and how they're connected

      A physical server that runs VMs is called a virtualized host.

Schematic illustration of virtualized computing.

Schematic illustration of cloud computing.

      Network Virtualization

      By definition, computer networks are already virtual because they're just an abstraction of physical connections. But in the context of cloud computing, network virtualization refers to virtual private clouds (VPCs)—isolated private networks within the cloud that allow connectivity among virtual machines and other cloud resources. There's some overlap with machine virtualization here, because VMs have virtual network interfaces that connect to these virtual private clouds.

      Cloud Service Models

      If a cloud provider controls all the hardware aspects of your IT infrastructure, what do you get to control? The answer depends on the type of cloud service model you choose. Cloud service models fall into three categories, all of which are characterized by the term as a service:

       Software as a Service (SaaS)

       Infrastructure as a Service (IaaS)

       Platform as a Service (PaaS)

      Many cloud service providers use more descriptive terms in their marketing, including Communications as a Service (CaaS), Anything as a Service (XaaS), Desktop as a Service (DaaS), and Business Process as a Service (BPaaS), to name a few. However, all of these clever names fit into the SaaS, IaaS, or PaaS categories.

      Software as a Service

      The capability provided to the consumer is to use the provider's applications running on a cloud infrastructure. The applications are accessible from various client devices through a thin client interface such as a web browser (e.g., web-based e-mail), or a program interface. The consumer does not manage or control the underlying cloud infrastructure including network, servers, operating systems, storage, or even individual application capabilities, with the possible exception of limited user-specific application configuration settings.

Schematic illustration of SaaS.

      Business applications are good examples of SaaS and can include customer relationship management, enterprise resource planning, human resources, payroll, and software development applications. Hosted applications such as email or calendars that are accessible from a browser or email client are examples of SaaS.

      Infrastructure as a Service

      The Infrastructure as a Service (IaaS) model lets you create VMs and virtual networks in the cloud according to your desired specifications regarding processing power, memory, storage, and networking. The IaaS model is probably the easiest to understand because it most closely mirrors the virtualized server environments in modern data centers. NIST describes it as follows:

      IaaS is really just a server and network virtualization environment offered as a service. Because of this, it offers the customer the most flexibility of any of the e-service models. You can provision to your specifications any number of VMs, on which you can run the software of your choice. Also, some IaaS offerings even allow you to choose the virtualized host on which your VMs run, giving you the ability to spread VMs across multiple hosts for resiliency.