This MS-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 uses Infrastructure-as-a-Service (IaaS) from a cloud provider. They have deployed virtual machines running a custom application. The cloud provider supplies the physical hardware, networking, and storage. Who is responsible for patching the operating system of the virtual machines?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The customer
In an IaaS model, the cloud provider is responsible for the physical infrastructure (hardware, networking, storage), but the customer retains responsibility for the guest OS and application stack. Patching the operating system of virtual machines is a customer task because the customer controls the OS image and has full administrative access to the VM. This follows the shared responsibility model where the provider secures the hypervisor and physical layer, while the customer secures the OS and applications.
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.
✗
The cloud provider
Why it's wrong here
The provider manages physical security and infrastructure, not the guest OS in IaaS.
✓
The customer
Why this is correct
In IaaS, the customer is responsible for securing and patching the operating system and applications on the virtual machines.
Related concept
Read the scenario before looking for a memorised answer.
✗
Both the provider and the customer share equally
Why it's wrong here
Responsibilities are divided; the provider handles the host, the customer handles the guest OS.
✗
A third-party managed security service provider
Why it's wrong here
While the customer could hire a third-party, the default responsibility lies with the customer under the IaaS model.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse IaaS with PaaS or SaaS, assuming the cloud provider patches everything, but in IaaS the customer is explicitly responsible for the guest OS and applications.
Detailed technical explanation
How to think about this question
Under the shared responsibility model, the provider maintains the hypervisor (e.g., Hyper-V, VMware ESXi) and physical host OS, while the customer is responsible for the guest OS, including applying security patches (e.g., Windows Update, yum/apt on Linux). In real-world scenarios, if a customer fails to patch the OS and a vulnerability like CVE-2021-34527 (PrintNightmare) is exploited, the cloud provider is not liable—the customer must remediate. This distinction is critical for compliance frameworks like SOC 2 or PCI DSS, where the customer must demonstrate OS patch management.
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
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this MS-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: The customer — In an IaaS model, the cloud provider is responsible for the physical infrastructure (hardware, networking, storage), but the customer retains responsibility for the guest OS and application stack. Patching the operating system of virtual machines is a customer task because the customer controls the OS image and has full administrative access to the VM. This follows the shared responsibility model where the provider secures the hypervisor and physical layer, while the customer secures the OS and applications.
What should I do if I get this MS-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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