AZ-900 Describe cloud concepts Practice Question
A company runs a legacy database on a single Azure virtual machine. The database is experiencing performance issues as the dataset grows. The IT team decides to increase the virtual machine size from Standard_D2s_v3 (2 vCPUs, 8 GB RAM) to Standard_D8s_v3 (8 vCPUs, 32 GB RAM) to improve performance. This process is an example of which cloud computing concept?
⚠ Common exam trap
Test-takers frequently confuse vertical scaling with elasticity, mistakenly thinking that any change in resource capacity is elasticity, but elasticity specifically requires automated, dynamic scaling based on demand, not a manual VM resize.
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
✓
Vertical scaling
Vertical scaling (also known as scaling up) involves increasing the capacity of a single resource, such as adding more vCPUs and RAM to an existing virtual machine. In this scenario, the IT team is resizing the Azure VM from Standard_D2s_v3 to Standard_D8s_v3, which increases the compute and memory resources of the same instance. This directly matches the definition of vertical scaling, where performance is improved by upgrading the existing machine rather than adding more machines.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Horizontal scaling
Why it's wrong here
Horizontal scaling, or scaling out, involves adding more virtual machines or instances to distribute the workload across multiple resources, often behind a load balancer. The scenario explicitly states that the company runs the database on a single Azure VM and increases its size, which is a textbook example of vertical scaling, not horizontal scaling. Since no additional VM instances are being deployed, this option does not match the described action.
When this WOULD be correct
A scenario where a company adds more virtual machines to a load-balanced set to handle increased traffic, such as adding extra web servers during a sales event, would be horizontal scaling.
- ✓
Vertical scaling
Why this is correct
Vertical scaling, also known as scaling up, increases the compute capacity of a single VM by selecting a larger VM size with more vCPUs, memory, and I/O performance. In this scenario, the IT team is resizing the existing virtual machine, which directly boosts the resources available to the legacy database without adding any new instances. This is a manual, one-time change, not an automated response to demand.
- ✗
Elasticity
Why it's wrong here
Elasticity is a cloud characteristic that refers to automatically scaling resources up or down in real time based on changing workload demand, typically using autoscaling rules. The scenario describes a deliberate manual resizing of a single VM rather than an automated, dynamic adjustment to fluctuating load patterns. Because the change is not triggered by demand conditions and does not happen automatically, characterizing it as elasticity would be incorrect.
When this WOULD be correct
A scenario where a web application automatically adds or removes virtual machines based on CPU utilization thresholds, such as using Azure VM Scale Sets with autoscale rules to handle traffic spikes, would make elasticity the correct answer.
- ✗
High availability
Why it's wrong here
High availability is the ability of a system to remain operational and fault-tolerant by architecting redundancy, such as running multiple VMs in an availability set or across availability zones, so that hardware failures or maintenance events do not cause downtime. Resizing a VM to a larger size improves its performance and capacity, but it does not introduce redundancy or protect the database against the failure of that single physical host. Therefore, this change is about scaling performance, not about ensuring continuous availability in the face of component failures.
When this WOULD be correct
A company runs a critical web application on two Azure VMs in an availability set. To ensure the application remains accessible during planned maintenance or a single VM failure, they configure both VMs in a load-balanced set. This is an example of high availability.
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.
✓Vertical scalingCorrect answer▾
Why this is correct
Vertical scaling, also known as scaling up, increases the compute capacity of a single VM by selecting a larger VM size with more vCPUs, memory, and I/O performance. In this scenario, the IT team is resizing the existing virtual machine, which directly boosts the resources available to the legacy database without adding any new instances. This is a manual, one-time change, not an automated response to demand.
✗Horizontal scalingWrong answer — click to see why▾
Why this is wrong here
The question describes increasing the size of a single VM (more vCPUs and RAM), which is vertical scaling. Horizontal scaling would involve adding more VMs, not resizing an existing one.
★ When this WOULD be the correct answer
A scenario where a company adds more virtual machines to a load-balanced set to handle increased traffic, such as adding extra web servers during a sales event, would be horizontal scaling.
Why candidates choose this
Candidates may confuse scaling up (vertical) with scaling out (horizontal) because both involve increasing resources; they might think any performance improvement via scaling is horizontal.
✗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 manually increasing the VM size. In this scenario, the scaling is a manual, one-time change to a larger VM size, not an automatic response to workload fluctuations.
★ When this WOULD be the correct answer
A scenario where a web application automatically adds or removes virtual machines based on CPU utilization thresholds, such as using Azure VM Scale Sets with autoscale rules to handle traffic spikes, would make elasticity the correct answer.
Why candidates choose this
Candidates may confuse scaling up (vertical scaling) with the concept of elasticity because both involve adjusting resources, but elasticity specifically implies automated, dynamic scaling in response to changing demand.
✗High availabilityWrong answer — click to see why▾
Why this is wrong here
High availability refers to ensuring system uptime through redundancy and failover, not to increasing resource capacity of a single VM. The question describes scaling up resources, not adding redundancy.
★ When this WOULD be the correct answer
A company runs a critical web application on two Azure VMs in an availability set. To ensure the application remains accessible during planned maintenance or a single VM failure, they configure both VMs in a load-balanced set. This is an example of high availability.
Why candidates choose this
Candidates may confuse scaling (vertical/horizontal) with availability concepts, thinking that improving performance also implies higher availability, or they may misinterpret 'high availability' as a general term for better performance.
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?”
Go deeper
Related to this question
Learn chapter
What is Cloud Computing?
Key term
Azure virtual machine
An Azure virtual machine is a software-based emulation of a physical computer that runs in Microsoft's cloud, allowing you to deploy and manage applications without owning the hardware.
Key term
Cloud computing
Cloud computing is the on-demand delivery of IT resources over the internet, allowing users to access computing power, storage, and applications without owning physical hardware.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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