Virtualization and Key Properties of Virtual Machines

Virtualization

Virtualization is not a new thing in IT industry. Virtualization gained huge momentum because of Vmware as it has solved the problem of running multiple OS and apps on one physical computer. But that is just the tip of the iceberg, Vmware and other virtualization vendors has given great features like Clustering of Virtualized Physical machines, pooling compute resources, storage pooling, High availability, Live migration of virtual machine and so much more. In this chapter we will understand virtualization, its benefits and how to use it for our DevOps day to day operations.

The Virtual Machine

A virtual computer system is known as a “virtual machine” (VM): a tightly isolated software container with an operating system and application inside. Each self-contained VM is completely independent. Putting multiple VMs on a single computer enables several operating systems and applications to run on just one physical server, or “host”.

Key Properties of Virtual Machines

VMs have the following characteristics, which offer several benefits.
Partitioning
Run multiple operating systems on one physical machine
Divide system resources between virtual machines
Isolation
Provide fault and security isolation at the hardware level
Preserve performance with advanced resource controls
Encapsulation
Save the entire state of a virtual machine to files
Hardware Independence
Provision or migrate any virtual machine to any physical server

Hypervisors

As generally we install OS on the physical server and then install our apps on that. By setting up Hypervisor on the physical server we can create multiple VMs each with their own OS.

There are two types of hypervisors:

Type 1 

hypervisors run directly on the system hardware. They are often referred to as a "native" or "bare metal” hypervisors.

They get installed on a physical computer like an OS. So instead of installing OS we install Hypervisor to achieve virtualization.

Example: 

Microsoft Hyper-V 

VMware ESX/ESXi. 

Xen Hypervisors 

These hypervisors are used to run production grade virtual machines that gives great performance. Type 1 hypervisors can be grouped together(clustered) and manged centrally by a software like Vmware Vcenter for Esxi.

Type 2 

Type 2 hypervisors run on a host operating system. In this kind, we install hypervisor on the OS like Linux or windows.

Example: 

Vmware server/workstation/player 

Oracle virtualbox.