AZ-900 Describe cloud concepts Practice Question
What is a key difference between vertical scaling and the benefit of cloud elasticity?
⚠ Common exam trap
Watch out — candidates often confuse vertical scaling with elasticity, assuming both provide automatic capacity adjustments without downtime, but elasticity specifically refers to the automated horizontal scaling that maintains availability, whereas vertical scaling typically requires manual intervention and downtime.
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 resizes one resource while elasticity adds/removes instances automatically without downtime
Vertical scaling (scaling up) increases the capacity of a single resource, such as adding more RAM or CPU to a virtual machine, but it typically requires downtime to apply the changes. Cloud elasticity, on the other hand, automatically adds or removes instances (horizontal scaling) based on demand, often without downtime, enabling the system to handle variable workloads seamlessly. Option B correctly captures this distinction by contrasting the resizing of one resource with the automated, no-downtime addition or removal of instances.
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 works faster than horizontal scaling
Why it's wrong here
Vertical scaling is generally slower in practice because it usually requires a VM restart to apply the new size, causing a period of unavailability. Horizontal scaling can add new instances that start and become available in minutes, and because existing instances keep running, there is no interruption; automated autoscale can react quickly to load changes. Thus, horizontal scaling often responds faster and with less operational impact than vertical scaling, especially in live production environments.
- ✓
Vertical scaling resizes one resource while elasticity adds/removes instances automatically without downtime
Why this is correct
Vertical scaling changes the size or tier of a single resource, such as moving a VM to a larger SKU, which often requires stopping and restarting the instance to apply the change. Elasticity, by contrast, automatically adds or removes identical instances based on real-time demand, spreading load across them without interrupting existing operations. This distinction is fundamental: vertical scaling resizes one resource, while elasticity manages a fleet of instances dynamically and without downtime.
- ✗
Vertical scaling is more cost-effective than elasticity for all workloads
Why it's wrong here
Vertical scaling's cost-effectiveness is workload-dependent, not universal. For steady, predictable workloads, scaling up a single VM might be simpler, but for variable or spiky demand, elasticity (horizontal scaling) lets you pay only for the instances you need at any moment, avoiding over-provisioning. Moreover, vertical scaling often requires downtime to resize, which can incur productivity costs, and it hits hardware limits, making it less flexible and often more expensive for dynamic workloads.
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Both vertical and horizontal scaling require manual intervention in cloud environments
Why it's wrong here
Horizontal scaling can be fully automated in cloud environments through autoscale rules that trigger instance additions or removals based on metrics like CPU utilization or request count, requiring no manual intervention. Vertical scaling, however, typically requires a manual step to change the VM's size or tier, and often a restart. So the claim that both require manual intervention is false because elasticity's whole purpose is to operate automatically.
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