AZ-900 Describe cloud concepts Practice Question
A company runs a web application that experiences unpredictable traffic spikes. They want the cloud to automatically increase the number of virtual machine instances during high demand and decrease them when demand drops, without manual intervention. Which cloud computing characteristic does this describe?
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
✓
Elasticity
Elasticity is the ability of a cloud system to dynamically scale resources up and down based on real-time demand. Scalability refers to the ability to handle growth but may not be automatic. High availability focuses on uptime, and fault tolerance ensures operation during failures. This scenario specifically describes automatic scaling, which is elasticity.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Elasticity
Why this is correct
Elasticity is correct because the application's unpredictable workload demands automatic resource adjustments. Azure Elasticity, implemented through Autoscale and VM Scale Sets, adds or removes instances on the fly based on metrics like CPU or request count, without manual intervention. This ensures the application can absorb sudden spikes in load and consume fewer resources during lulls, optimizing cost and performance. It is the only option that directly addresses the need for dynamic, demand-driven scaling.
- ✗
Scalability
Why it's wrong here
Scalability is incorrect because it refers to the capability to handle increased load by expanding resources, but it may be a manual or scheduled operation. While Azure supports both vertical scalability (increasing VM size) and horizontal scalability (adding instances), the unpredictable nature of the workload requires automatic scaling adjustments. Predefined scaling settings, such as scheduled scale-out for predictable traffic, do not suffice for random spikes. Elasticity is the automatic subset of scalability that specifically matches the scenario.
When this WOULD be correct
A question asking: 'A company expects steady growth in user traffic over the next year and wants to add more virtual machines manually each quarter. Which cloud characteristic is this?' would make scalability the correct answer, as it involves planned, manual capacity increases.
- ✗
High availability
Why it's wrong here
High availability is incorrect because it emphasizes uptime and accessibility of the application, typically achieved through redundancy and load balancing across availability zones or regions. It ensures that the service remains reachable even if one component or data center goes down, but the number of processing instances stays primarily static. High availability does not involve dynamically adding or removing resources based on real-time demand. An available system can still become unresponsive under extreme load if it lacks elasticity, so this option fails to address the unpredictable workload.
When this WOULD be correct
A question that asks for the characteristic describing a system designed to remain operational and accessible for a very high percentage of time, such as 99.99% uptime, often through redundancy across multiple availability zones.
- ✗
Fault tolerance
Why it's wrong here
Fault tolerance is incorrect because it focuses on maintaining system operation in the face of component failures, not on responding to demand changes. Techniques such as redundant components, failover clusters, and data replication ensure that the system continues to function if a server, disk, or network fails. The app could be fully fault-tolerant yet still be overwhelmed by an unexpected surge in traffic, as fault tolerance does not inherently adjust resource capacity. The question's core requirement is automatic scaling, not resilience to failures.
When this WOULD be correct
A question asks: 'A company needs its application to continue running without interruption even if a virtual machine fails. Which cloud characteristic is this?' Fault tolerance would be correct.
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.
✓ElasticityCorrect answer▾
Why this is correct
Elasticity is correct because the application's unpredictable workload demands automatic resource adjustments. Azure Elasticity, implemented through Autoscale and VM Scale Sets, adds or removes instances on the fly based on metrics like CPU or request count, without manual intervention. This ensures the application can absorb sudden spikes in load and consume fewer resources during lulls, optimizing cost and performance. It is the only option that directly addresses the need for dynamic, demand-driven scaling.
✗ScalabilityWrong answer — click to see why▾
Why this is wrong here
Scalability refers to the ability to handle increased load by adding resources, but it does not inherently imply automatic adjustment based on demand. This question specifically describes automatic scaling in response to unpredictable spikes, which is the defining characteristic of elasticity.
★ When this WOULD be the correct answer
A question asking: 'A company expects steady growth in user traffic over the next year and wants to add more virtual machines manually each quarter. Which cloud characteristic is this?' would make scalability the correct answer, as it involves planned, manual capacity increases.
Why candidates choose this
Candidates often confuse scalability with elasticity because both involve adding resources. The key difference is automation: scalability can be manual or planned, while elasticity is automatic and dynamic.
✗High availabilityWrong answer — click to see why▾
Why this is wrong here
High availability focuses on ensuring the application remains accessible and operational despite failures, not on automatically adjusting capacity in response to traffic spikes.
★ When this WOULD be the correct answer
A question that asks for the characteristic describing a system designed to remain operational and accessible for a very high percentage of time, such as 99.99% uptime, often through redundancy across multiple availability zones.
Why candidates choose this
Candidates may confuse high availability with elasticity because both involve handling variable demand, but high availability is about uptime and redundancy, not dynamic scaling.
✗Fault toleranceWrong answer — click to see why▾
Why this is wrong here
Fault tolerance ensures system operation during component failures, not automatic scaling based on demand. The question describes adjusting resources to match traffic spikes, which is elasticity.
★ When this WOULD be the correct answer
A question asks: 'A company needs its application to continue running without interruption even if a virtual machine fails. Which cloud characteristic is this?' Fault tolerance would be correct.
Why candidates choose this
Candidates may confuse fault tolerance with elasticity because both involve handling unexpected events, but fault tolerance focuses on failure recovery, not demand-based scaling.
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
Fault tolerance
Fault tolerance is the ability of a system to continue operating properly even when one or more of its components fail.
Key term
Elasticity
Elasticity is the ability of a cloud system to automatically add or remove computing resources (like servers, storage, or bandwidth) in response to real-time changes in demand.
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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.