Easy Notes of Cloud Computing unit- 2 @Computer Diploma

Description

2.1 Introduction & Reference Model

• Definition: The process of creating a software-based (virtual) representation of something (servers, storage, networks) rather than a physical one.

• Hypervisor (VMM): The “Virtual Machine Monitor” that abstracts hardware. It sits between the physical hardware and the Virtual Machines.

• Virtualization Reference Model:

  1. Hardware Layer: Physical CPU, RAM, Disk.

  2. Virtualization Layer: The Hypervisor.

  3. Virtual Machine Layer: Guest OS and Applications.

• Characteristics:

  • Partitioning: Running multiple OS on one physical machine.

  • Isolation: If one VM crashes, others are unaffected.

  • Encapsulation: A VM is stored as a single file (easy to move/copy).

2.2 Types of Virtualization

• Storage Virtualization: Pooling physical storage from multiple devices into what appears to be a single storage unit (e.g., SAN).

• Network Virtualization: Splitting available bandwidth into independent channels (e.g., VLANs, VPNs).

• Desktop Virtualization (VDI): Hosting a desktop OS on a central server; users access their “PC” from any device.

• Application Server Virtualization: Wrapping an application in its own isolated environment (layer) so it doesn’t conflict with the host OS.

2.3 & 2.4 Technology Examples: VMware vs. Xen

• VMware (Full Virtualization):

  • Binary Translation: Used to trap and emulate privileged instructions.

  • Reference Model: The Guest OS is unaware it is being virtualized; no modification to the Guest OS is needed.

• Xen (Para-virtualization):

  • Hypercells: The Guest OS is modified to communicate directly with the hypervisor.

  • Domain 0 (Dom0): A privileged management VM that controls other “Guest” VMs (DomU).

2.5 VM Life Cycle & Management

• VM Life Cycle: Create $\rightarrow$ Provision $\rightarrow$ Use $\rightarrow$ Maintain $\rightarrow$ Retire/Delete.

• VM Migration: Moving a VM from one physical host to another.

  • Live Migration: Moving while the VM is running (zero downtime).

  • Cold Migration: Powering off the VM before moving.

• VM Consolidation: Combining multiple VMs onto a single physical server to increase resource utilization and save power.

• VM Management: Monitoring performance, security, and resource allocation across the virtual fleet.

2.6 Advantages & Disadvantages (Short Keywords)

Quick Recall Keywords for Exams:

• Abstraction: Hiding physical details.

• Multi-tenancy: Sharing resources among many users.

• Hypervisor Type-1: Native/Bare-metal (e.g., ESXi, Xen).

• Hypervisor Type-2: Hosted (e.g., VirtualBox, VMware Workstation).

• Snapshot: Capturing the state of a VM at a specific time.