What Is Cloud Computing? IaaS, PaaS and SaaS

TL;DR

• Cloud computing means using computers, storage and software that someone else runs, over the internet, and using only what you need when you need it [1].
• There are three main service models: IaaS (rented machines), PaaS (a ready-made platform for your app) and SaaS (a finished app you simply use).
• A public cloud is open to the general public, while a private cloud is used by a single organization [5][6].
• "The cloud" is not a mysterious place. It is other people's computers, in data centers, shared out on demand.

What the cloud is #

Years ago a company that wanted a website or an internal system had to buy servers, house them, and look after them. Cloud computing changes that. NIST, the US standards body, describes it as a model for convenient, on-demand network access to a shared pool of computing resources such as servers, storage, applications and services, which can be quickly set up and released with little effort from the provider [1].

Think of electricity. You do not build a power station to run your kettle. You plug in and pay for what you use. Cloud services work in a similar way: you ask for more computing power when you are busy and hand it back when you are not.

Gmail, Netflix, online banking and photo backups all run this way. The program is not on your device. It runs in a provider's data center, and your phone or laptop just talks to it.

IaaS, PaaS and SaaS #

The three service models differ in how much of the work you do yourself and how much the provider does.

A handy way to remember it is a pizza analogy. IaaS is buying the ingredients and a kitchen, PaaS is a ready-made base where you add the toppings, and SaaS is having the pizza delivered.

The more you move from IaaS toward SaaS, the less you control, but the less you have to maintain. Most people use SaaS every day without noticing. Developers and IT teams are more likely to work with IaaS and PaaS.

Public vs private clouds #

The service models describe what you rent. The deployment model describes who shares the infrastructure with you.

• Public cloud. Infrastructure open for use by the general public. It may be owned and run by a business, a university or a government body, and it sits on the provider's premises [5].
• Private cloud. Infrastructure used exclusively by one organization with several users or business units. It can be run by the organization or an outside party, and located on site or off site [6].
• Hybrid cloud. NIST describes four deployment models in total [1]. A hybrid setup is commonly described as a mix of the two, such as keeping sensitive records in a private cloud while using a public cloud for everything else.

Public does not mean your data is visible to everyone. Customers are kept separate by the provider's security controls. What matters in practice is who runs it, who else shares it, and what rules or contracts apply to your data.

Why people use the cloud #

• Pay for what you use. You avoid buying hardware that sits idle.
• Scale up or down. Capacity can grow for a busy period and shrink afterwards.
• Less maintenance. The provider looks after the hardware, and in PaaS and SaaS often much more besides.
• Access from anywhere. You need only a device and an internet connection.

There are trade-offs: you depend on your provider and your connection, costs can grow if usage is not watched, and you still have to protect your own accounts and settings.

FAQ #

Is the cloud just someone else's computer? #

Largely, yes. The computers are in data centers run by a provider, and you reach them over the internet. What makes it "cloud" is that the resources are shared out on demand rather than bought one machine at a time [1].

What is the difference between SaaS and PaaS? #

With SaaS you use a finished application, like web email. With PaaS you get an environment in which you deploy an app you built or acquired, and you manage that app rather than the underlying servers [3][4].

Is a private cloud more secure than a public cloud? #

Not automatically. A private cloud is used by one organization, but security depends on how any system is configured and maintained. A well-run public cloud can be safer than a poorly run private one, so judge each on its controls.

Do I use cloud computing already? #

Very likely. Web email, streaming video, online documents and phone photo backups are all examples of SaaS.

Sources #