The main service models 

So, the Cloud offers us computing services which anyone can access just like an on-demand utility. But how does it actually do this?  

Well, cloud computing services are categorised in to three primary models depending on the type of service that’s being provided.  

Let’s have a look at each one. 

Infrastructure as a service is the most basic category of cloud computing services and relates to the IT infrastructure, so things like servers and virtual machines, storage, networks and operating systems. 

Through IaaS, an organisation can re-create their IT infrastructure by defining networks in the cloud, having application servers that run inside those networks, and installing and configuring application software on those servers – as long as their software licenses allow it! 

Effectively this is what an organisation would do in their own data centers but instead, they do it in the cloud provider’s data centers. That means the provider takes care of hardware provision but the organisation still has a large degree of control over exactly what software’s running in the cloud. 

Imagine your organisation needs a database server to capture data from your customer service system. You could use IaaS to create a server and install database management software on it. But you could also leave this to the cloud provider who can provide and configure the resources behind the scenes and give you secure access to those resources.  

So, Platform as a service is the model that provides an on-demand environment for developing, testing, delivering and managing software applications using provider-managed building blocks. However, whilst this approach means having slightly less control over the configuration of the services, it also means the organisation has less responsibility for the infrastructure that’s running them, freeing them up to focus on adding new features and services rather than maintaining the technical infrastructure.  

Software as a service is the model for delivering software applications on-demand over the Internet, typically on a subscription basis. With SaaS, cloud providers host and manage the software application and underlying infrastructure, and handle any maintenance, like software upgrades and security patching. Users connect to the application over the Internet, usually with a web browser on their phone, tablet or PC. 

Examples of SaaS applications you might use include things like salesforce.com, Microsoft Office 365 and Google Apps.  

The organisation’s only responsibility is for configuring end-user access, and company-specific data and settings. Users access SaaS applications through a user interface and an application programme interface – or API – which enables developers to customise and integrate the software with existing data and applications.  

The SaaS model means the organisation has the least control over the infrastructure but the fewest responsibilities. 

Fancy a pizza? 

Let’s take a step outside of IT for a moment and look at the three cloud service models in a different way.   

You eat a lot of pizzas and fancy one again tonight. There’s a few different options you could go with – you could make it and cook it yourself, you could buy a pizza and cook it at home, you could get one delivered or you could go to the lovely Italian restaurant up the road where they could do everything for you.  

Some of these options will cost you more than the others, balanced against the effort you take to prepare the pizza. They probably also provide different degrees of quality and choice.   

Let’s take a closer look at these options based on the cloud service models. To make it simple, we’ll assume that the different elements are getting the ingredients for the dough base and the toppings, having an oven to cook the pizza in and having a table and chairs to eat it on. Oh, and you’ll probably need a drink to go with it. Think of these as the different resources that you’ll need and you might have to pay for. 

The first option is that you could make it from scratch at home. You’ll probably get exactly what you want, cooked how you like it, but you’ll need to go to all the effort to buy the ingredients, make the pizza and cook it. Apart from the time and effort this takes – you’ll have the risk of missing an ingredient or burning the pizza, and what if your oven breaks down. Making it from scratch is the IT equivalent of being self-sufficient in-house – buying managing and upgrading the full IT infrastructure hardware, software and storage. 

The second option is to buy the pizza at the supermarket and cook it at home. You provide the oven, table, chairs and drinks but you pay somebody else to prepare the pizza. Less effort than making it yourself but you’re restricted by the types of pizzas you can get and you have to pay to get the pizza prepared. Think of this as the infrastructure as a service equivalent – you’ve acquired the ‘resource’ of the pre-prepared pizza or, in IT terms, the server in the cloud. 

Then you could get a pizza delivered. Again, less choice than making it yourself but you don’t even need to cook it. Just find somewhere to eat it, get a drink and put in the effort to order it. This is perhaps the platform as a service equivalent where there are several components working together to provide a single seamless service – the people who make and cook the pizza and the people who deliver it.  

And then, the final option where you don’t actually have to do anything – the restaurant takes care of it all. Yes, it’s more expensive but you’re happy to pay that for the convenience, quality, choice and the fact that you don’t need to worry about forgetting anything. You could even buy it on your credit card so you can pay for it later! So, this is the software as a service equivalent – it’s the entire application which you use and get billed for. 

So, think of cloud services as providing resources in the cloud – things that a provider can provide at a cost. In infrastructure as a service, a resource could refer to a single server. In platform as a service a resource could refer to several components working together to provide a single service, and in software as a service a resource could be the entire application, or an individual component in that application.