This chapter covers Azure Virtual Machines, one of the most fundamental IaaS compute services in Azure. AZ-900 tests this under objective 2.2, "Describe Azure compute and networking services."
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A simple way to picture Azure Virtual Machines
Building your own physical server is like constructing an office building from scratch — you handle the foundation, wiring, and structure yourself. Renting a virtual machine is like renting a fully built office space instead: the building (physical hardware) is already there, managed by someone else, and you just move in and configure the space (operating system and applications) to suit your needs. You can also choose an office of a specific size for your needs, and move to a bigger or smaller one later without constructing anything yourself.
What a Virtual Machine is
An Azure Virtual Machine (VM) is a software-based emulation of a physical computer, running on Azure's underlying physical infrastructure. It gives the customer control over the operating system and everything installed on top of it, while Azure manages the physical hardware beneath it — the classic IaaS pattern covered in the service models chapter.
How it works
When a VM is created, the customer selects a VM size (determining CPU, memory, and other resource allocations), an operating system image, storage options, and networking configuration. Azure provisions the underlying physical resources and presents the customer with what behaves like a dedicated computer, even though it's running on shared physical hardware alongside other customers' VMs, isolated from each other.
Key components and options
VM size: determines available CPU, memory, and other resources — chosen based on the workload's needs.
Operating system image: Windows or Linux, either a standard image or a custom one.
Storage: managed disks attach to the VM for its operating system and data.
Networking: VMs connect to virtual networks (covered in a separate chapter) to communicate with other resources and the internet.
How it compares to on-premises servers
A physical, on-premises server requires purchasing hardware upfront, physically installing and maintaining it, and generally sizing it for peak expected demand. An Azure VM can be resized, or additional VMs added, relatively quickly compared to procuring and installing new physical hardware.
Portal and CLI touchpoints
az vm create --resource-group myRG --name myVM --image Ubuntu2204 --size Standard_B2sThe Azure portal offers an equivalent "Create a virtual machine" wizard covering the same choices.
Choose a VM size
VM sizes determine available CPU, memory, and other resources, and are chosen based on the specific workload's requirements — a size that's too small may underperform, while an oversized one wastes cost.
Select an operating system image
A base Windows or Linux image is selected (or a custom image), which becomes the starting point for the VM's operating system.
Configure storage and networking
Managed disks are attached for the operating system and data storage, and the VM is connected to a virtual network so it can communicate with other resources.
Manage and maintain the VM
Once running, the customer is responsible for operating-system-level maintenance (patching, updates) and anything installed on top, per the Shared Responsibility Model.
A company migrating a legacy application that requires a specific operating system configuration uses an Azure VM to host it, since it needs the OS-level control that IaaS provides, without the constraints of a more managed platform service.
A separate team running a temporary, resource-intensive data-processing job provisions a larger VM size for the duration of the job, then resizes or deletes it afterward — taking advantage of the ability to adjust capacity as needed rather than owning fixed hardware sized for that occasional peak.
Objective 2.2 expects candidates to understand what an Azure Virtual Machine is, that it's an IaaS offering, and the responsibilities that come with using one under the Shared Responsibility Model.
A common wrong answer is assuming Azure manages the VM's operating system — under IaaS, the customer is responsible for OS-level maintenance, including patching. Another common trap is not recognizing that VM size, storage, and networking are all separate, configurable choices rather than a single fixed package.
Stable terms: Virtual Machine, VM size, managed disk. Recognizing Azure VMs as the canonical IaaS compute example is one of the most reliable facts to know for scenario-based questions.
Memory trick: a VM is IaaS — Azure manages the physical hardware, the customer manages everything from the operating system up.
An Azure Virtual Machine is an IaaS compute offering — Azure manages the physical infrastructure, the customer manages the operating system and above.
VM size, operating system image, storage, and networking are all separately configurable choices.
Per the Shared Responsibility Model, the customer is responsible for OS-level maintenance and patching on a VM.
VMs can generally be resized after creation, offering more flexibility than fixed physical hardware.
These come up on the exam all the time. Here's how to tell them apart.
Azure Virtual Machine (IaaS)
Customer manages OS and above; Azure manages hardware
Can be resized or scaled relatively quickly
No physical maintenance for the customer
Usage-based ongoing cost
Physical On-Premises Server
Customer manages the entire stack, including hardware
Resizing means buying and installing new hardware
Customer handles all physical maintenance
Large upfront capital cost
Mistake
Azure automatically patches the operating system on a VM.
Correct
Under IaaS, OS-level maintenance, including patching, is the customer's responsibility — Azure manages only the physical infrastructure and virtualization layer beneath the VM.
Mistake
A VM's size can't be changed after it's created.
Correct
VM size can generally be changed after creation (with some downtime depending on the resize), letting a workload adjust to more or less demand over time.
Mistake
Virtual machines are the only compute option in Azure.
Correct
Azure offers several compute options beyond VMs — including App Service, Azure Functions, and container services — each suited to different needs, covered in their own chapters.
It's a software-based emulation of a computer running on Azure's infrastructure, giving the customer control over the operating system and everything installed on top, while Azure manages the underlying physical hardware — a classic example of the IaaS service model.
The customer is, under the Shared Responsibility Model — Azure manages the physical infrastructure and virtualization layer, but operating-system-level maintenance, including patching, is the customer's responsibility for IaaS resources like VMs.
Generally yes — VM size can typically be changed after creation, though this may require some downtime depending on the specific resize. This offers more flexibility than being stuck with fixed physical hardware sizing.
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