Describe Cloud Concepts · Topic 3 of 3
Cloud Service Types
Compare IaaS, PaaS and SaaS for AZ-900: what each one means, who manages what, Azure examples and the use cases the exam asks about.
- 4 min
- IaaS gives virtual machines, storage and networks. You manage the operating system.
- PaaS gives a managed platform. You manage only your application and data.
- SaaS is complete software. You manage only your data, users and settings.
What it is
Cloud services come in three main types. They differ in how much of the technology stack you manage and how much the provider manages.
The names are Infrastructure as a Service (IaaS), Platform as a Service (PaaS) and Software as a Service (SaaS). More provider management means less control for you and less work.
How it works
Infrastructure as a Service
IaaS gives you the basic building blocks: virtual machines, storage and networks. You choose the operating system, install software and keep it patched.
Microsoft manages the physical hardware. An Azure virtual machine is the standard example.
Use IaaS to move an existing application without changing it (often called lift and shift), for testing and development environments, and when you need full control of the operating system.
Platform as a Service
PaaS gives you a managed platform on which to build and run applications. The provider looks after the servers, the operating system and the runtime, so you work only on your code and data.
Examples are Azure App Service for web apps and Azure SQL Database for relational data.
Use PaaS to build and host applications quickly without administering servers, and when developers should focus on features instead of maintenance.
Software as a Service
SaaS is finished software delivered over the internet, usually by subscription. The provider runs everything, and you manage only your data, users and settings.
Microsoft 365 and Dynamics 365 are examples.
Use SaaS when a ready made application meets the need, such as email or customer management.
Who manages what
| Item | IaaS | PaaS | SaaS |
|---|---|---|---|
| Physical hardware and datacenter | Provider | Provider | Provider |
| Operating system | You | Provider | Provider |
| Application | You | You | Provider |
| Your data and users | You | You | You |
Serverless sits beside PaaS
Serverless services such as Azure Functions go one step further than PaaS. You provide only the code, and the platform runs it on demand and bills for execution.
Choosing a type from the need
Exam questions describe a need and ask for the type. Look for who manages the operating system and the application.
| The need | Type |
|---|---|
| Move an existing application to the cloud without changing it | IaaS |
| Install and patch your own operating system | IaaS |
| Build and host a web API without managing servers | PaaS |
| Store relational data without managing a database server | PaaS |
| Give staff email and office tools | SaaS |
| Run a small function when a file is uploaded | Serverless, a form of PaaS |
Who patches what
Patching shows the difference most clearly.
| Item | IaaS | PaaS | SaaS |
|---|---|---|---|
| Operating system updates | You | Microsoft | Microsoft |
| Runtime and platform updates | You | Microsoft | Microsoft |
| Application code and its fixes | You | You | Microsoft |
| User accounts and data | You | You | You |
Azure examples by type
- IaaS: Azure Virtual Machines, Azure Virtual Network and Azure managed disks.
- PaaS: Azure App Service, Azure SQL Database and Azure Functions.
- SaaS: Microsoft 365 and Dynamics 365.
Many solutions mix types. A company might run a legacy application on a virtual machine, its new website on App Service, and use Microsoft 365 for email, all at once.
How the exam asks about this
- "Which service type requires the customer to manage the operating system?" IaaS.
- "Which type lets developers focus only on code?" PaaS.
- "Which type is Microsoft 365?" SaaS.
- A virtual machine is IaaS even though the provider runs the hardware. If you must patch the guest operating system, it is IaaS.
- If a question says the customer manages nothing but their data and users, think SaaS.
What to remember for the exam
- IaaS gives virtual machines, storage and networks. You manage the operating system.
- PaaS gives a managed platform. You manage only your application and data.
- SaaS is complete software. You manage only your data, users and settings.
- Typical examples: Azure virtual machines for IaaS, Azure App Service for PaaS, Microsoft 365 for SaaS.
- The more managed the service, the less control you have and the less you maintain.
- IaaS fits lift and shift and full control. PaaS fits fast application development. SaaS fits ready made needs.
If the question mentions installing or patching an operating system, the answer is IaaS. If it says "no servers to manage but I write the code", think PaaS or serverless.
Common mistakes
Calling a virtual machine PaaS. A virtual machine is IaaS, because you manage the operating system.
Thinking SaaS means no responsibility. You still manage your data, users and access.
Forgetting that the choice is a trade off. More control means more work, and less work means less control.
Treating serverless as a fourth type. It is an evolution of PaaS where billing follows execution.
Check yourself
Which service type lets you install and patch your own operating system?
Infrastructure as a Service.
Which type is Microsoft 365?
Software as a Service.
In PaaS, who manages the operating system?
The cloud provider.
Topic 3 of 3 in Describe Cloud Concepts
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