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.
An e-commerce application runs in the cloud and automatically adjusts the number of virtual machines based on real-time traffic. When traffic spikes, more VMs are added; when traffic drops, VMs are removed. Which cloud computing characteristic does this behavior exemplify?
Elasticity allows resources to be automatically scaled out (added) and scaled in (removed) to match workload changes.
B
Measured service
Why wrong: Measured service refers to the monitoring and billing of resource usage, not the dynamic scaling of resources.
C
Resource pooling
Why wrong: Resource pooling is about serving multiple customers from a shared pool of physical resources, not automatic scaling.
D
On-demand self-service
Why wrong: On-demand self-service allows users to provision resources without human interaction, but the scenario specifically describes scaling based on load, which is elasticity.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Rapid elasticity
Rapid elasticity is the cloud characteristic that enables resources to scale out (add VMs) and scale in (remove VMs) automatically in response to real-time demand. In this e-commerce scenario, the application adjusts VM count based on traffic spikes and drops, which directly matches the definition of rapid elasticity as defined by NIST SP 800-145.
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.
✓
Rapid elasticity
Why this is correct
Elasticity allows resources to be automatically scaled out (added) and scaled in (removed) to match workload changes.
Related concept
Read the scenario before looking for a memorised answer.
✗
Measured service
Why it's wrong here
Measured service refers to the monitoring and billing of resource usage, not the dynamic scaling of resources.
✗
Resource pooling
Why it's wrong here
Resource pooling is about serving multiple customers from a shared pool of physical resources, not automatic scaling.
✗
On-demand self-service
Why it's wrong here
On-demand self-service allows users to provision resources without human interaction, but the scenario specifically describes scaling based on load, which is elasticity.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse 'on-demand self-service' (manual provisioning by the user) with 'rapid elasticity' (automatic scaling), because both involve responding to demand, but only elasticity handles real-time, automated adjustments without user intervention.
Trap categories for this question
Scenario analysis trap
On-demand self-service allows users to provision resources without human interaction, but the scenario specifically describes scaling based on load, which is elasticity.
Detailed technical explanation
How to think about this question
Under the hood, rapid elasticity is often implemented via auto-scaling groups (e.g., AWS Auto Scaling, Azure VM Scale Sets) that use metrics like CPU utilization or request count to trigger scale-out or scale-in actions. A subtle behavior is the cooldown period (e.g., 300 seconds in AWS) that prevents flapping—rapidly adding and removing VMs due to transient spikes. In a real-world scenario, an e-commerce site during Black Friday might scale from 10 to 500 VMs in minutes, then scale back down as traffic normalizes.
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.
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: Rapid elasticity — Rapid elasticity is the cloud characteristic that enables resources to scale out (add VMs) and scale in (remove VMs) automatically in response to real-time demand. In this e-commerce scenario, the application adjusts VM count based on traffic spikes and drops, which directly matches the definition of rapid elasticity as defined by NIST SP 800-145.
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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