Cloud computing and virtualisation

It’s common to hear someone talk about something being ‘in the cloud’, but what actually is cloud computing and how does it work?

In this step you’re going to explore the answers to these questions and take a look at the underlying principles of cloud computing, and the benefits of the cloud.

What is cloud computing?

“A model for enabling ubiquitous, convenient, on-demand network access to a shared pool of configurable resources (e.g. networks, servers, storage, applications, and services) that can be rapidly provisioned and released with minimal management effort or service provider interaction.”

Simply put, cloud computing lets us quickly deploy and access a range of IT resources anytime anyplace without the hassle usually associated with running and maintaining such services and infrastructure.

The ‘cloud’ refers to powerful banks of servers kept in datacentres around the world that are available for anyone with an internet connection. The services available range from phone back-up storage and consumer applications to entire IT set-ups mirroring large on-premises solutions.

Cloud users don’t need to worry about maintaining or updating these datacentres – the cloud provider takes care of that – the users just access and pay for the services they require.

There are different models of cloud services which you’ll look at in more detail in the next step, but, for now, here are some essential characteristics of cloud computing:

• On-demand and self-service
• Broad network access
• Resource pooling
• Rapid elasticity
• Measure service

Why is everyone moving to the cloud?

You can probably already identify a few reasons why the cloud is attractive to individual consumers and organisations alike. Here’s an overview of some of those benefits.

Two of the big bonuses – especially for organisations – are scalability and elasticity:

Scalability refers to the ability to increase or decrease IT resources as needed to meet changing demand. This contrasts with on-premises IT where you’d need enough resources to meet peak demand, meaning you’ve paid for something you won’t always be using.

Elasticity is the ability to quickly expand or decrease computer processing, memory and storage resources to meet changing demands. This is easy to do with cloud computing with the ability to provision resources in a matter of minutes, if not seconds.

When no longer needed, these resources can be handed back to the cloud provider and the user incurs no further charger as they’re not in use. With on-premises IT, buying and installing extra hardware resources is expensive and requires expertise to install and maintain.

The differences between scalability and elasticity

Here are some other benefits of cloud computing:

• Reduced IT complexity
• Reduced risk
• Faster access to resources
• Staff access from multiple sources
• Greater business agility
• Increased mobility
• Easier collaboration and innovations

How does cloud computing actually work?

To answer this question, you need to know what virtualisation is, but it’s worth reviewing a few details about physical computers first, as a point of comparison.

A typical physical computer

A computer is made up of different hardware such as a processor, memory, a hard disk for storage, and so on. There is just one operating system (OS) which talks directly to the hardware and applications running on top of this OS.

How does virtualisation differ?

Virtualisation allows you to run two or more OSs from one physical computer. It’s a way of using the hardware to create one or more software-based virtual computers – called virtual machines (VMs). A VM is similar to a physical computer in that it has components such as a processor and memory, but these are virtual. It also needs an OS to be installed and managed for applications to run.

Figure 1: A physical machine and a virtual machine.

Virtualisation is possible through the use of a piece of software called a hypervisor, also called a virtual machine monitor (VMM), that sits between the physical hardware and a VM. The hypervisor makes sure that each VM has access to the physical resources it needs to run. A computer on which a hypervisor runs one or more VMs is called a host machine, and each VM is called a guest machine.

There are two types of hypervisor:

Type 1 or ‘bare metal’ hypervisors

This type of hypervisor interacts directly with the underlying hardware, there’s no need for any OS to be installed on the hardware.

Type 2

This type of hypervisor runs as an application on an OS that has been installed onto the hardware. This means there’s usually a hit to performance as the hardware is running both the OS that the hypervisor runs off and the virtualised OS.

Figure 2: Type 1 and Type 2 hypervisors.

Simply put, virtualisation is a way for two or more virtual machines to run on a single set of hardware. This is done through the use of a hypervisor which interacts directly with the hardware (Type 1) or is installed on the hardware’s pre-existing OS (Type 2).

And when it comes to cloud computing it’s not just one computer at work, it is huge datacentres around the globe with banks of powerful servers providing virtualised resources for cloud users.

What’s next?

With the underlying principle of cloud computing clarified, it’s time to explore how this has been exploited in practice. You’ll start with a recap of the different models for cloud computing and the types of services offered by cloud providers.