IaaS, PaaS, SaaS: A Beginner's Guide to the Cloud

This guide provides a basic explanation of the most common cloud models: IaaS (Infrastructure-as-a-Service), PaaS (Platform-as-a-Service) and SaaS (Software-as-a-Service) using examples from Microsoft’s cloud — Microsoft Azure.


When a business runs its IT Infrastructure on-premise, the business is responsible for everything. The company must source, purchase, maintain and manage the infrastructure itself—which takes time, expertise and money. It is the business’ responsibility to fix a failing server, maintain backups and pay for the energy costs of the infrastructure (among a host of other considerations). You might have the company servers sitting in a room a few metres from the desks where your employees work.

Infrastructure-as-a-Service (IaaS)

With the cloud (e.g. Microsoft Azure), you have the option of something called Infrastructure-as-a-Service (IaaS). This is where you let Microsoft take care of the IT infrastructure for your business—saving your IT department time, effort and possibly money (depending on a range of factors).

Microsoft have huge hyper-scale Azure data centres in various locations globally. These data centres are packed full of thousands of racks of servers and IT infrastructure. With IaaS, you can move your company data, applications and operating systems etc. to the cloud. A common method of doing this involves a simple “lift and shift” process—where you move your virtual machines from on-premise to the cloud.

The different cloud models: IaaS, PaaS and SaaS.

As you can see from above, IaaS means that Microsoft will look after your networking, storage, servers and virtualisation. When you pay for this, you’ll have access to Virtual Machines in Azure. After choosing which operating systems (O/S) to use (made available as pre-built templates), you would be responsible for managing your O/Ss such as Windows on these virtual machines and managing all your business applications and data.

IAAS Summary

  • With IaaS you pay to use Microsoft’s infrastructure and for them to manage it.
  • You can migrate your company data and applications etc. to Azure and run it on Microsoft’s infrastructure.

Platform-as-a-Service (PaaS)

PaaS is a cloud service model that might be of interest companies and / or developers where they want to develop, host and deploy applications. Rather than building applications and services on-premise, PaaS allows you to build these applications and services directly in the cloud.

Take a look at image above again: you’ll see that PaaS includes the same infrastructure services that are included with IaaS. However, Microsoft also manage the operating systems with PaaS.

What does this mean? It means that Microsoft can provide the tools that a business would need to quickly develop, test and deploy apps—while removing the complexities around the infrastructure and platforms that are needed to do so. It essentially allows the developers to focus on the development, testing and deployment of apps with quicker timescales.

PAAS Summary

  • Your company will manage the apps and data, but you’re paying Microsoft to take care of the rest of the underlying infrastructure and platform.

Software as a Service (SaaS)

SaaS is where a company pays for ready-to-use software solutions on a subscription-basis without having to worry about the IT that goes with it. That means you don’t need to manage and maintain the underlying infrastructure, platforms or software—you can just start using the software.

SaaS can take all kind of forms. Any software service that runs in the cloud is SaaS.

An example of this is Microsoft Dynamics 365—a cloud-based CRM system that you can access using any browser such as Chrome, Edge or Safari. The Dynamics 365 software is completely managed by Microsoft. That means Microsoft look after everything that is needed to run the software such as servers, storage, databases etc. While you are paying for a subscription, Microsoft will make sure you are always updated to the latest versions of the software and take care of everything else. You can just focus on using the applications for your day-to-day business.

Traditionally, if you’d have purchased CRM software to be used on-premise, you’d have bought a single licence that would not be automatically updated, and you’d need to manage all of the IT to support the software (e.g. configuring the databases and running it on the on-premise servers etc.). You’d also have needed to purchase newer versions of the software to keep up to date and get access to the latest features. By using the cloud equivalent of that software, you don’t need to worry about any of this—it’s managed for you.

Many pieces of software (developed by various companies) are now available on subscriptions, run directly from Azure.

SAAS Summary

  • SaaS is where you can pay for software on a subscription-basis.
  • You don’t need to manage any of the IT that supports the software—that will be taken care of for you.

Which model is right for different situations?

SaaS is a great model (where possible) due it’s affordability, reliability and flexibility; the cloud provider also handles everything, allowing you to focus on adding significant business value—rather than worrying about things such as patching your software and O/Ss. With SaaS, the software is typically affordable (including all costs of regular updates, maintenance and customer support), quick to deploy and doesn’t require any infrastructure. Typically, you will also benefit from very high levels of uptime, security and backup/recovery features.

In respect of PaaS, rather than building applications and services on your on-premise servers, PaaS allows you to build these applications and services directly in the cloud. The flexibility of PaaS services means that you can choose the features you want and those you don’t. All your infrastructure and platform requirements are taken care of, allowing you to focus on your applications and data.

There are instances where IaaS is your best option, although we tend to look towards SaaS where possible. For example, it would be advisable to opt for IaaS if you are running legacy software that isn’t available online (as SaaS) due to its age. In this instance, migrating the server to the cloud would likely be the optimal solution. If IaaS is something you’re considering, find out how you can make 80% savings by using Azure Reserved Instances.

Considering the cloud?

Are you considering moving elements of your IT to the cloud? If so, get in touch with us for a chat with one of our friendly cloud experts. We’ll make sure that you implement best practices and take the optimal approach to your cloud transition—while minimising risks.