The customer is responsible for securing the operating system on an Azure virtual machine. This is because, under the shared responsibility model for Infrastructure as a Service (IaaS), Microsoft secures the physical host, hypervisor, and network infrastructure, while the customer retains full control over the guest OS, including applying patches, configuring firewalls, and managing applications. On the AZ-900 exam, this distinction tests your understanding of how responsibility shifts based on service type—a common trap is assuming Microsoft handles OS security for VMs, when in fact the customer owns everything above the hypervisor. A helpful memory tip is to visualize a line at the hypervisor: Microsoft owns the hardware and host, you own the guest OS and everything inside the VM.
AZ-900 Describe cloud concepts Practice Question
This AZ-900 practice question tests your understanding of describe cloud concepts. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company wants to understand who is responsible for securing the operating system on an Azure virtual machine. According to the shared responsibility model, who is responsible?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Microsoft is responsible for the physical host and network, while the customer is responsible for the guest OS and applications.
Under the shared responsibility model for IaaS like Azure VMs, Microsoft secures the physical datacenter, host OS, and network infrastructure, while the customer is responsible for securing the guest OS (e.g., applying patches, configuring firewalls) and any applications running on the VM. This division is explicit in Azure's documentation, where the customer retains control over the OS and software stack.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Microsoft is responsible for all security.
Why it's wrong here
Incorrect. Microsoft secures the cloud infrastructure, but customers secure what they put in the cloud, especially with IaaS.
✗
The customer is responsible for all security.
Why it's wrong here
Customers are responsible for their own data and configurations, but Microsoft provides physical security and network controls.
✓
Microsoft is responsible for the physical host and network, while the customer is responsible for the guest OS and applications.
Why this is correct
Correct. This describes the shared responsibility model for IaaS.
Related concept
Read the scenario before looking for a memorised answer.
✗
Responsibility is split 50/50.
Why it's wrong here
The split is not an even percentage; it depends on the service type. For IaaS, customers handle more than 50% of the security controls.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume Microsoft handles all OS security for Azure VMs because of the 'as a service' branding, but in IaaS, the customer retains full responsibility for the guest OS and applications, unlike PaaS or SaaS where Microsoft manages more layers.
Detailed technical explanation
How to think about this question
In Azure, the hypervisor (e.g., Hyper-V) isolates VMs, and Microsoft manages the host OS and physical hardware via the Azure Fabric Controller. The customer must configure the guest OS firewall (e.g., Windows Firewall or iptables), apply security updates via WSUS or Azure Update Management, and manage application-level security (e.g., TLS certificates). A real-world scenario: if a customer fails to patch the guest OS against CVE-2023-23397, Microsoft is not liable for the resulting compromise, as they only guarantee the hypervisor isolation.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this AZ-900 question in full detail.
Describe cloud concepts — This question tests Describe cloud concepts — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Microsoft is responsible for the physical host and network, while the customer is responsible for the guest OS and applications. — Under the shared responsibility model for IaaS like Azure VMs, Microsoft secures the physical datacenter, host OS, and network infrastructure, while the customer is responsible for securing the guest OS (e.g., applying patches, configuring firewalls) and any applications running on the VM. This division is explicit in Azure's documentation, where the customer retains control over the OS and software stack.
What should I do if I get this AZ-900 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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