➤ The Internet is a huge collection of computers connected in a communications network.
➤ The Transmission Control Protocol/Internet Protocol (TCP/IP) became the standard for computer network connections in 1982.
➤ Rather than connecting every computer on the Internet directly to every other computer on the Internet, normally the individual computers in an organization are connected to each other in a local network. One node on this local network is physically connected to the Internet.
➤ So, the Internet is actually a network of networks, rather than a network of computers.
➤ Obviously, all devices connected to the Internet must be uniquely identifiable.

 Virtualization is mainly used to emulate execution environments, storage, and networks.

Process-level techniques are implemented on top of an existing operating system, which has full control of the hardware.

System-level techniques are implemented directly on hardware and do not require or require a minimum of support from an existing operating system.

 Operating System Level Virtualization

• To create different and separated execution environments for applications that are managed concurrently.
• There is no virtual machine manager or hypervisor, and the virtualization is done within a single operating system.
• OS kernel allows for multiple isolated user space instances.
• chroot mechanism in Unix systems. The chroot operation changes the file system root directory for a process and its children to a specific directory.
• The process and its children cannot have access to other portions of the file system.

Programming language-level virtualization

• To achieve ease of deployment of applications, managed execution, and portability across different platforms and operating systems.
• It consists of a virtual machine executing the byte code of a program, which is the result of the compilation process.
• Generally these virtual machines constitute a simplification of the underlying hardware instruction set and provide some high-level instructions that map some of the features of the languages compiled for them.
• Basic Combined Programming Language
• Both Java and the CLI are stack-based virtual machines.

Application-level virtualization

• Such emulation is performed by a thin layer - a program or an operating system component that is in charge of executing the application.
• Interpretation - In this technique every source instruction is interpreted by an emulator for executing native ISA instructions, leading to poor performance.
• Binary translation - In this technique every source instruction is converted to native instructions with equivalent functions. After a block of instructions is translated, it is cached and reused.
• SaaS utilizes application-level virtualization to deploy the application

 

• In a virtualized environment there are three major components: guest, host, and virtualization layer.
• The guest represents the system component that interacts with the virtualization layer rather than with the host, as would normally happen.
• The host represents the original environment where the guest is supposed to be managed.
• The virtualization layer is responsible for recreating the same or a different environment where the guest will operate
• in the case of hardware virtualization, the guest is represented by a system image Compromising an operating system & installed application
• These are installed on top of Virtual hardware that is controlled & managed by the Virtualization layer also called Virtual machine mangager

 Advantages of Virtualization

• Managed execution and isolation are perhaps the most important advantages of virtualization.
• allow building secure and controllable computing environments.
• This enables fine tuning of resources, which is important in a server consolidation and is also a requirement for effective quality of service
• Portability especially for execution virtualization techniques
• Java programs are compiled once and run every where. they only require that the java Virtual Machine be installed on the host.
• To achieve a more efficient use of resources the underlying host, without interfering with each other.

Disadvantages of Virtualization

• Performance degradation since virtualization interposes an abstraction layer b/w the guest and the host , the guest can experience increased latencies
• Binary transition and interpretation can slow down the execution of managed applications
• inefficiency and degraded user explain leads to an experience leads to an inefficient use of the host
• Some of the specific features of the host cannot be exposed by the abstraction layer and then become an inaccesible
• Security holes and new threats opens the door to a new and unexpected form of phishing

 Machine reference model
Modern computing systems can be expressed in terms of the reference model described in below Figure At the bottom layer, the model for the hardware is expressed in terms of the Instruction Set Architecture (ISA), which defines the instruction set for the processor, registers, memory, and interrupt management. ISA is the interface between hardware and software, and it is important to the operating system (OS) developer (System ISA) and developers of applications that directly manage the underlying hardware (User ISA). The application binary interface (ABI) separates the operating system layer from the applications and libraries, which are managed by the OS. ABI covers details such as low-level data types, alignment, and call conventions and defines a format for executable programs.

The highest level of abstraction is represented by the application programming interface (API), which interfaces applications to libraries and/or the underlying operating system.

a possible implementation features a hierarchy of privileges (see Figure 3.5) in the form of ring-based security: Ring 0, Ring 1, Ring 2, and Ring 3; Ring 0 is in the most privileged level and Ring 3 in the least privileged level. Ring 0 is used by the kernel of the OS, rings 1 and 2 are used by the OS-level services, and Ring 3 is used by the user. Recent systems support only two levels, with Ring 0 for supervisor mode and Ring 3 for user mode.

 Development of a cloud computing application happens by leveraging platforms and frameworks that provide different types of services, from the bare-metal infrastructure to customizable applications serving specific purposes.

1. Amazon web services (AWS)
2. Google AppEngine
3. Microsoft Azure
4. Hadoop
5. Force.com and Salesforce.com
6. Manjrasoft Aneka

 Popek and Goldberg provided a classification of the instruction set and proposed three theorems that define the properties that hardware instructions need to satisfy in order to efficiently support virtualization.

Theorem 1: For any conventional third-generation, a VMM maybe constructed if the set of sensitive instructions for that computer is a set of privileged instructions.

This theorem establishes that all the instructions that change the configuration of the system resources should generate a trap in user mode and be executed under the control of the virtual machine manager.

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Theorem 2:A conventional third-generation computer is recursively if:

1. It is virtualizable and
2. A VMM without any timing dependencies can be constructed for it.

Recursive virtualization is the ability to run a virtual machine manager on top of another virtual machine manager. This allows nesting hypervisors as long as the capacity of the underlying resources can accommodate that. Virtualizable hardware is a prerequisite to recursive virtualization.

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THEOREM 3: A hybrid VMM may be constructed for any conventional third-generation machine in which set of user-sensitive instructions is a subset of the set of privileged instructions.
There is another term, hybrid virtual machine (HVM), which is less efficient than the virtual machine system. In the case of an HVM, more instructions are interpreted rather than being executed directly. All instructions in virtual supervisor mode are interpreted. Whenever there is an attempt to execute a behavior-sensitive or control-sensitive instruction, HVM controls the execution directly or gains the control via a trap. Here all sensitive instructions are caught by HVM that are simulated.

 A fundamental characteristic of cloud computing is the capability to deliver, on demand, a variety of IT services that are quite diverse from each other.

cloud computing services offerings into three major categories: Infrastructure-as-a-Service (IaaS), Platform-as-a-Service (PaaS), and Software-as- a-Service (SaaS). These categories are related to each other as described in Figure 1.5, which provides an organic view of cloud computing.

At the base of the stack, Infrastructure-as-a-Service solutions deliver infrastructure on demand in the form of virtual hardware, storage, and networking. Virtual hardware is utilized to provide compute on demand in the form of virtual machine instances.

Platform-as-a-Service solutions are the next step in the stack. They deliver scalable and elastic runtime environments on demand and host the execution of applications. These services are backed by a core middleware platform that is responsible for creating the abstract environment where applications are deployed and executed.

At the top of the stack, Software-as-a-Service solutions provide applications and services on demand. Most of the common functionalities of desktop applications. Each layer provides a different service to users. IaaS solutions are sought by users who want to leverage cloud computing from building dynamically scalable computing systems requiring a spe- cific software stack. IaaS services are therefore used to develop scalable Websites or for back- ground processing.

 Microsoft Azure is a cloud operating system and a platform for developing applications in the cloud. Applications in Azure are organized around the concept of roles, which identify a distribution unit for applications and embody the application’s logic. Currently, there are three types ofrole: Web role, worker role, and virtual machine role. The Web role is designed to host a Web application, the worker role is a more generic container of applications and can be used to perform workload processing, and the virtual machine role provides a virtual environment in which the computing stack can be fully customized, including the operating systems.