Horizontal Scaling: Adding More VMs to Handle Increased Load
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?
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.”
⚠ Common exam trap
It's easy for candidates to 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).
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.
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 increases the size or power of an existing VM; the team added five separate VMs, leaving each instance unchanged. It is tempting because scale up also handles increased load, and would be correct if they had resized the three existing VMs to larger SKUs instead.
When this WOULD be correct
Vertical scaling would be correct if the question described increasing the resources (CPU, RAM) of existing virtual machines, such as resizing each VM to a larger SKU, without adding new instances.
- ✓
Horizontal scaling (scale out)
Why this is correct
Adding five more virtual machines to the existing pool increases the instance count from three to eight. Horizontal scaling, or scaling out, adds more instances of the same resource to distribute load, rather than resizing an existing VM's CPU or memory.
- ✗
Elasticity
Why it's wrong here
Elasticity is the ability to automatically match provisioned resources to demand; the stem describes a manual addition of five VMs, with no automation or scale-in mentioned. It is tempting because elasticity also concerns handling load changes, but it requires automatic, dynamic provisioning rather than a one-off manual action.
When this WOULD be correct
A question asking: 'A company's web application automatically adds or removes VMs based on CPU utilization. What cloud characteristic does this demonstrate?' would make Elasticity the correct answer.
- ✗
High availability
Why it's wrong here
High availability concerns redundant components surviving failure, not adding capacity for load; the stem describes demand-driven growth from three to eight VMs. It is tempting because both involve multiple VMs, and HA designs do run several instances, but availability addresses outages, not traffic volume.
When this WOULD be correct
A question that asks: 'Which feature ensures that a web application remains accessible even if one of its Azure VMs fails?' would have high availability as the correct answer, as it focuses on uptime and fault tolerance rather than scaling.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The AZ-900 exam frequently reuses these exact scenarios with slightly different constraints.
✓Horizontal scaling (scale out)Correct answer▾
Why this is correct
Adding five more virtual machines to the existing pool increases the instance count from three to eight. Horizontal scaling, or scaling out, adds more instances of the same resource to distribute load, rather than resizing an existing VM's CPU or memory.
✗Vertical scaling (scale up)Wrong answer — click to see why▾
Why this is wrong here
The team added more virtual machines (from 3 to 8), which increases the number of instances, not the size of each instance. This is horizontal scaling, not vertical scaling.
★ When this WOULD be the correct answer
Vertical scaling would be correct if the question described increasing the resources (CPU, RAM) of existing virtual machines, such as resizing each VM to a larger SKU, without adding new instances.
Why candidates choose this
Candidates may confuse 'scaling up' with any increase in capacity, not realizing that vertical scaling specifically means increasing the power of existing resources rather than adding more of them.
✗ElasticityWrong answer — click to see why▾
Why this is wrong here
Elasticity refers to the ability to automatically scale resources up or down based on demand, not the act of manually adding VMs. The question describes a manual addition of VMs, not an automated response to load changes.
★ When this WOULD be the correct answer
A question asking: 'A company's web application automatically adds or removes VMs based on CPU utilization. What cloud characteristic does this demonstrate?' would make Elasticity the correct answer.
Why candidates choose this
Candidates confuse the concept of elasticity (automatic scaling) with the scaling action itself, or they think any scaling scenario involves elasticity.
✗High availabilityWrong answer — click to see why▾
Why this is wrong here
High availability refers to ensuring that applications remain operational despite failures, typically through redundancy and failover mechanisms, not by adding more VMs to handle increased load.
★ When this WOULD be the correct answer
A question that asks: 'Which feature ensures that a web application remains accessible even if one of its Azure VMs fails?' would have high availability as the correct answer, as it focuses on uptime and fault tolerance rather than scaling.
Why candidates choose this
Candidates may confuse the concept of adding more VMs (scaling out) with the goal of maintaining availability, mistakenly thinking that increasing capacity directly equates to high availability.
Analysis generated from the official AZ-900blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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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.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This AZ-900 practice question is part of Courseiva's free Microsoft certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the AZ-900 exam.