- A
Vertical scaling (scale up)
Why wrong: Vertical scaling (scale up) would involve increasing the size (e.g., CPU, RAM) of the existing virtual machines, not adding more instances.
- B
Horizontal scaling (scale out)
Horizontal scaling (scale out) adds more instances of the same size to distribute the load across multiple VMs, which matches the described action of adding five more VMs.
- C
Elasticity
Why wrong: Elasticity is the ability of a system to automatically scale resources up or down based on real-time demand. Although the scenario involves scaling, the action was performed manually by the IT team, not automatically.
- D
High availability
Why wrong: High availability refers to keeping the application running and accessible despite failures, often through redundancy and failover mechanisms. This scenario is about scaling to handle increased load, not about ensuring uptime during failures.
Quick Answer
The answer is horizontal scaling (scale out). This is correct because horizontal scaling increases capacity by adding more virtual machines to a pool, distributing the workload across additional instances rather than upgrading a single machine. In the scenario, moving from three to eight VMs directly demonstrates this concept, as the team added five new VMs to handle the promotional surge. On the Microsoft Azure Fundamentals AZ-900 exam, this question tests your ability to distinguish horizontal scaling from vertical scaling, where vertical scaling would instead increase the size (CPU, RAM) of existing VMs. A common trap is confusing the two when the question mentions “adding resources,” but remember: horizontal means more machines, vertical means bigger machines. For a quick memory tip, think of “horizontal” as “hiring more workers” versus “vertical” as “giving one worker a bigger desk.”
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 runs a web application on Azure virtual machines. During a promotional event, the number of users increases significantly. To handle the increased load, the IT team adds five additional virtual machines to the existing pool, so that the total number of VMs increases from three to eight. Which type of scaling is the team using?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Horizontal scaling (scale out)
Horizontal scaling (scale out) involves increasing the number of virtual machines (VMs) in a pool to distribute load, as seen when the team adds five VMs to go from three to eight. This approach improves capacity by adding more instances, rather than increasing the size of existing ones. In Azure, this is commonly achieved using Virtual Machine Scale Sets or Azure Load Balancer to distribute traffic across the expanded pool.
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.
- ✗
Vertical scaling (scale up)
Why it's wrong here
Vertical scaling (scale up) would involve increasing the size (e.g., CPU, RAM) of the existing virtual machines, not adding more instances.
- ✓
Horizontal scaling (scale out)
Why this is correct
Horizontal scaling (scale out) adds more instances of the same size to distribute the load across multiple VMs, which matches the described action of adding five more VMs.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Elasticity
Why it's wrong here
Elasticity is the ability of a system to automatically scale resources up or down based on real-time demand. Although the scenario involves scaling, the action was performed manually by the IT team, not automatically.
- ✗
High availability
Why it's wrong here
High availability refers to keeping the application running and accessible despite failures, often through redundancy and failover mechanisms. This scenario is about scaling to handle increased load, not about ensuring uptime during failures.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse the term 'elasticity' (a cloud attribute) with the specific scaling action of adding or removing instances, leading them to pick Option C instead of recognizing that the question explicitly asks for the type of scaling (horizontal vs. vertical).
Trap categories for this question
Scenario analysis trap
Elasticity is the ability of a system to automatically scale resources up or down based on real-time demand. Although the scenario involves scaling, the action was performed manually by the IT team, not automatically.
Detailed technical explanation
How to think about this question
Under the hood, horizontal scaling in Azure often relies on Azure Load Balancer with a backend pool of VMs, distributing incoming traffic using a hash-based distribution algorithm (e.g., 5-tuple hash for TCP/UDP). Virtual Machine Scale Sets automate this by allowing you to define autoscale rules based on metrics like CPU percentage or queue depth, enabling dynamic scale-out and scale-in. A real-world scenario involves a retail website during Black Friday, where scale-out handles sudden traffic spikes without requiring downtime for resizing individual VMs.
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.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this AZ-900 question test?
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: Horizontal scaling (scale out) — Horizontal scaling (scale out) involves increasing the number of virtual machines (VMs) in a pool to distribute load, as seen when the team adds five VMs to go from three to eight. This approach improves capacity by adding more instances, rather than increasing the size of existing ones. In Azure, this is commonly achieved using Virtual Machine Scale Sets or Azure Load Balancer to distribute traffic across the expanded pool.
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.
About these practice questions
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Same concept, more angles
2 more ways this is tested on AZ-900
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company runs a web application in Azure that experiences variable traffic throughout the day. During peak hours, the application becomes slow because the existing virtual machine (VM) cannot handle the increased load. The solution architect proposes adding more VMs of the same size and distributing incoming requests across all of them to balance the load. Which scaling concept does this approach represent?
medium- A.Vertical scaling
- ✓ B.Horizontal scaling
- C.Elastic scaling
- D.Disaster recovery
Why B: Horizontal scaling (also known as scaling out) involves adding more virtual machines of the same size to distribute incoming traffic across them. In this scenario, adding more VMs of the same size and using a load balancer to distribute requests directly matches the definition of horizontal scaling, which increases system capacity by adding more instances rather than increasing the power of a single instance.
Variation 2. A company hosts a web application on a single Azure virtual machine. Over the past month, the application's CPU utilization has consistently remained above 90%, causing slow response times. The administrator plans to modify the virtual machine's size from Standard_D2s_v3 (2 vCPUs) to Standard_D8s_v3 (8 vCPUs) to improve performance. Which scaling method does this change represent?
medium- A.Horizontal scaling (scaling out)
- ✓ B.Vertical scaling (scaling up)
- C.Elastic scaling
- D.Auto-scaling
Why B: Vertical scaling (scaling up) increases the power of an existing resource by upgrading its size or capacity. In this scenario, changing the virtual machine from Standard_D2s_v3 (2 vCPUs) to Standard_D8s_v3 (8 vCPUs) adds more CPU cores to the same VM, which is a classic example of scaling up. This approach improves performance without adding additional VM instances.
Last reviewed: Jun 11, 2026
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