Cloud Reference ModelRamkumar Lakshminarayanan

Virtualization is abstracting the hardware to run virtual instances of multiple guest operating systems on a single host operating system.

You can see Virtualization in action by installing Microsoft Virtual PC, VMware Player or Sun VirtualBox.

These are desktop virtualization solutions that let you install and run an OS within the host OS.

There are many reasons for running Virtualization on the servers running in a traditional data center. Here are a few: Meantime to Restore Maximizing the server utilization Reduction in maintenance cost Efficient management

Typically the OS is designed to act as an interface between the applications and the hardware.

It is not specifically designed to run the guest OS instances on top of it.

Virtualization on the Server

In the server virtualization scenario, the host OS is not very significant.

OS is not ideal for running multiple VMs and has a little role to play, there is a new breed of software called Hypervisor that takes over the OS.

Hypervisor is an efficient Virtual Machine Manager (VMM) that is designed from the ground up to run multiple high performance VMs. So, a Hypervisor is to VMs what an OS is to processes.

A Hypervisor can potentially replace the OS and can even boot directly from a VM. This is called bare metal approach to virtualization.

These Hypervisors have low footprint of few megabytes (vmWare ESXi is just 32MB in size!) and have an embedded OS with them.

Hypervisors are assisted by the hardware virtualization features built into the latest Intel and AMD CPUs.

This combination of hardware and Hypervisor turns the server into a lean and mean machine to host multiple VMs.

The VM that is used by the Hypervisor to boot as a host is called a paravirtualized VM.

This concept makes virtualization absolutely powerful.

Imagine a server booting in few seconds and the required paravirtualized (host) VM gets copied over a gigabit Ethernet to run multiple guest VMs.

This turns the datacenter to be very dynamic and agile.

Xen’s paravirtualization technology is widely acknowledged as the fastest and most secure virtualization software in the industry and it is enhanced by taking full advantage of the latest Intel® VT and AMD-V™ hardware virtualization assist capabilities.

It is free.

Citrix XenServer

This product is another bare metal Hypervisor from the virtualization leader, VMware. This is one of the best Hypervisors with just 32MB footprint.

ESXi ships with Direct Console User Interface (DCUI) that provides basic UI required for administering and managing the Hypervisor.

VMware ESXi

This is a free Hypervisor from Microsoft based on the same Hypervisor that ships with Microsoft Windows Server Hyper-V edition.

This is best suited for Virtual Desktop Infrastructure (VDI) because of its compatibility with Windows Vista and Windows 7. Hyper-V does not have any local GUI but can be managed from System Center Virtual Machine Manager (SCVMM).

Microsoft Hyper-V Server

Virtualization and the Cloud

We know that the key attribute of the Cloud is Elasticity, which is the ability to scale up and scale down on the fly.

This capability is achieved only through virtualization.

Scaling up is technically adding more server VMs to an application and scaling down is detaching the VMs from the application.

Elasticity

The Hypervisor comes with an API and the required agents to manage it remotely. This functionality can surface through the Self Service portals that the Cloud vendor offers.

So, when you move a slider to increase the number of servers in your web tier, you are essentially talking to the Hypervisor to action that request.

Self Service

By leveraging the management and monitoring capabilities of the Hypervisor, metering the usage of resources like the CPUs, RAM and storage can be easily achieved.

Pay-By-Use

Developers can directly talk to the Hypervisor through the native APIs or Web Services exposed by the Cloud vendors.

Through this, they can take the control of the VMs.

It is very obvious that the Cloud is heavily relying on virtualization and efficient Hypervisors to achieve its goal.

Programmable Infrastructure

Geographic location

Most of the Cloud providers give you an option to host your application at a specific location.

Depending on the customer base and the expected user location, you can choose a location.

This will ensure that all your components like storage, compute and database services are hosted within the same data center.

This will reduce the latency and makes the application more responsive Geographically.

Geographically Spread Data Center

Your app will be deployed at a data center physically located at a place that you have chosen.

These data centers typically run thousands of powerful servers that offer a lot of storage and computing power.

Data Center

A Cloud Data Center runs hundreds of Servers

You never know which physical server is responsible for running your code and the application.

In most of the cases, the app that you deployed may be powered by more than one server running within the same data center.

Servers are treated as a commodity resource to host the VMs. There is no affinity between a VM and a physical server.

Server

This is the layer that you will directly interact with. In Platform as a Service (PaaS), you may not realize that you are dealing with a VM but in reality most of the Cloud implementations will host your code or app on a VM.

Load balancer which will ensure that your applications are scalable by exploiting the power of all the VMs associated with your application.

Virtual Machine

Cloud Server

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