Cloud Resource Virtualization

Cloud Resource Virtualization

• Virtualization in computing is the process of simulating hardware and software in a virtual environment.
• Traditionally, businesses operated with one machine per application.
• Virtualization consolidates multiple physical servers, with their applications and operating systems, into a single physical server within a virtual environment.
• A single server can run multiple VMs (virtual machines), each running different applications and operating systems.
• The software that creates and runs virtualization is called a hypervisor, which allocates and controls a machine's resources.

Types of Hypervisors

• Type I hypervisors are installed on empty, bare metal hardware.
• Type II hypervisors run on top of an existing operating system and are typically used on personal computers for tasks like testing software or trying different operating systems.
• VMWare EXSI is an example of a type-1 hypervisor.
• Oracle VM VirtualBox, Microsoft Virtual PC, and VMware Workstation are examples of type-II hypervisors.

Benefits of Virtualization

• Saves money on hardware and electricity.
• Saves money on floor space
• Saves money on maintenance and management.
• Offers portability of virtual machines between physical machines.
• Allows full utilization of computing capability.
• Aids in disaster and recovery scenarios.

Portability

• If a virtual machine's current host is old or lacks space, it can be easily transferred to a more powerful machine.

Full Computing Capability

• Virtualization allows VMs to fully utilize a machine's processing power, whereas otherwise their potential is not being fully utilized.

Disaster and Recovery

• VMs are software files that can be backed up and uploaded to multiple physical machines.

Layering in Virtualization: 7-Layer Model

• Access Virtualization allows applications to work with remote client devices and enables access from any location. An example is XenDesktop from Citrix.
• Application Virtualization allows applications written for one OS version to run in another environment, like App-V from Microsoft.
• Processing Virtualization allows one system to support workloads as if it were many systems. Examples are Citrix XenServer and Microsoft Hyper-V.
• Network Virtualization allows systems to work with other systems safely and securely, without needing to know the details of the underlying network,
• Storage Virtualization allows workloads to access storage without needing to know the data's location or the type of device storing it, such as VMware VSAN.
• Security for Virtual Environment monitors and protects all other virtualization layers, allowing use of the resources to only authorized use.
• Management of Virtual Environment allows easy monitoring and management of virtual environments across boundaries by IT administrators and operators.

Virtual Machines

• A VM is like a virtual computer with the ability to run applications and store data, serving as a software-based emulation of a physical computer.
• VMs operate in an isolated environment and can run their own operating systems and applications.

Common Uses for VMs

• Building and deploying apps to the cloud.
• Trying out a new operating system (OS), including beta releases.
• Spinning up a new environment to make it simpler and quicker for developers to run dev-test scenarios.
• Backing up an existing OS.
• Accessing virus-infected data or running an old application by installing an older OS.
• Running software or apps on operating systems that they weren't originally intended for.

Types of Virtual Machines

• VMs are isolated environments that appear to be whole computers but only have partial access to the computer's resources.
• Process VMs are virtual platforms created for an individual process and destroyed after the process terminates.
• System VMs support an operating system with many user processes.
• Traditional VMs support multiple virtual machines and run directly on the hardware.
• Hybrid VMs share hardware with a host operating system and support multiple virtual machines.
• Hosted VMs run under a host operating system.

Benefits of VMs

• Running multiple virtual environments on one infrastructure piece reduces the physical infrastructure footprint, decreasing maintenance costs and electricity.
• Spinning up a VM is relatively easy and quick, making the process of running dev-test scenarios faster.
• VMs are portable and easily moved between hypervisors, making them a solution for backup in case the host goes down.
• Scaling apps is easier with VMs by adding more physical or virtual servers to distribute the workload, increasing availability and performance.
• Because VMs run in multiple operating systems, using a guest operating system on a VM allows users to run applications of questionable security and protects the host operating system, allowing for better security forensics and study of computer viruses, isolating the viruses.

Performance Isolation in Virtualization

• Resource Allocation: Virtualization platforms use resource allocation techniques to divide a host machine's physical resources among its VMs, allocating portions of the CPU, memory, disk space, and network bandwidth, done statically or dynamically.
• Resource Scheduling: The virtualization platform schedules the execution of VMs' workloads on the physical hardware, ensuring each VM gets its allocated resources and preventing resource contention,
• Resource Monitoring: The virtualization platform continuously monitors each VM's resource usage and the system performance, reallocating resources or migrating VMs to other hosts if needed.
• Quality of Service (QoS): Virtualization platforms support QoS policies.
• Isolation Mechanisms: Virtualization platforms implement isolation mechanisms, ensuring VMs do not interfere with each other that include CPU scheduling algorithms such as time-sharing or fair scheduling, memory protection mechanisms, and network traffic shaping.
• Performance Guarantees: Virtualization platforms offer performance guarantees with Service Level Agreements (SLAs).

Approaches to Virtualization

• Full Virtualization
• Paravirtualization
• Hardware-Assisted virtualization

Full Virtualization

• Full virtualization, mimics the functionality of physical computers, enabling the creation and operation of VMs.
• The guest OS is completely abstracted from the underlying infrastructure.
• The guest OS is unaware that it is virtualized.
• It requires hypervisors to interact with the underlying infrastructure.
• This approach uses binary translation and direct execution: binary translation translates nonvirtualized guest OS instructions, and direct execution is used for user application requests.
• Full virtualization uses a hypervisor layer to interact with the server's hardware resources and acts as a platform for all operating systems.
• Each virtual machine operates independently, providing a high degree of isolation. The guest OS is unaware of the underlying hardware infrastructure.
• The hypervisor manages and allocates physical resources to each VM.

Advantages of Full Virtualization

• Best isolation among VMs is achieved.
• Allows different operating systems to run simultaneously
• Virtual guest OS can be easily migrated to work in native hardware.
• It is easy to install and does not require any change in the guest OS.

Disadvantages of Full Virtualization

• Binary translation is an overhead that reduces overall system performance.
• Requires correct hardware and software combination
• VMWare EXS and VirtualBox are examples of full virtualization

Paravirtualization

• Involves modifying the guest operating system (OS) to be aware of the virtualization layer/hypervisor.
• Provides partial simulation of the underlying infrastructure.
• The main difference between the full virtualization and paravirtualization is the guest OS knoes that it is running in virtualized environment in paravirtualization.
• Paravirtualization replaces the translation of nonvirtualized OS requests with hypercalls, similar to system calls, and used for direct communication between the OS and hypervisor, which improves performance and efficiency.
• Full virtualization can use the guest OS without any modification, but paravirtualization needs to modify the guest OS.
• As the guest OS is at privileged position, it can communicate directly to the virtualization layer and replaces hardware instructions with hypercalls, improving performance.
• It requires a hypervisor, but the guest operating systems are aware of it, with the hypervisor providing a set of APIs for them to communicate with the hardware.
• The virtualization guest OS must be modified to replace certain hardware-related instructions with hypercalls, allowing the guest OS to request services from the hypervisor.
• A collaborative effort is required between the guest OS and the hypervisor.

Advantage of Paravirtualization

• Eliminates the overhead of binary translation, improving overall system efficiency and performance.
• Is easier to implement than full virtualization
• Xen and VMWare ESX server are examples of Paravirtualization

Disadvantage of Paravirtualization

• Requires new versions of OS to be deployed, as an older version will not have 'paravirtualization-awareness'
• Cannot migrate the modified guest OS to run on physical hardware.
• VMs suffer from lack of backward compatibility and are difficult to migrate to other hosts

Full Virtualization vs. Paravirtualization

• Guest OS Modification: Full virtualization requires no modification, while paravirtualization requires hypercalls.
• Performance: Full virtualization has slightly lower performance due to emulation, while paravirtualization has better performance due to direct interaction.
• Isolation: Full virtualization offers strong isolation between VMs, while paravirtualization offers isolation with awareness of other VMs.
• Guest OS Flexibility: Full virtualization supports various OS types, paravirtualization works best with compatible OSes.
• Hardware Compatibility: Full virtualization is compatible with most hardware, while paravirtualization requires hardware support.
• Hypervisor Layer: Full virtualization manages virtual hardware independently and paravirtualization provides APIs for communication.
• Interaction with Hardware: Full virtualization emulates complete hardware, while paravirtualization uses hypercalls.
• Examples: Full virtualization includes VMware, Hyper-V, VirtualBox; paravirtualization includes Xen, KVM, QEMU.
• Resource Overhead: Full virtualization has slightly higher resource overhead, paravirtualization has lower resource overhead.

Hardware Support for Virtualization

• Hardware support is crucial for optimizing the performance and efficiency of virtualized environments.
• Hardware vendors like Intel and AMD have developed processors with hardware extensions for virtualization.
• Intel offers Virtualization Technology (VT), including VT-x for x86 processors and VT-d for I/O virtualization.
• AMD offers AMD Virtualization (AMD-V) with features like AMD-Vi for I/O virtualization.
• Virtualization requires efficient memory management through features like hardware-assisted paging, such as Extended Page Table (EPT).
• Input/Output Virtualization enables VMs to interact with devices via Direct Memory Access (DMA).

Hardware Support: Pros

• Reduces the overhead of binary translation in full virtualization.
• Eliminates guest OS modification in paravirtualization.

Hardware Support: Cons

• Only newer processors support these virtualization features.
• More VM traps can result in high CPU overhead and limited scalability