AZ-900 Describe cloud concepts Practice Question
A company runs a web application on Azure App Service. During a marketing campaign, the application's traffic surges to five times its normal level. The application is configured to automatically add more instances to handle the increased load and then remove them when demand returns to normal. This ability to dynamically provision and de-provision resources based on real-time demand is a direct example of which cloud computing characteristic?
⚠ Common exam trap
A common mix-up: candidates confuse scalability (the ability to grow) with elasticity (the ability to both grow and shrink automatically), so they pick 'Scalability' without recognizing that the scenario explicitly mentions removing resources when demand returns to normal.
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
The scenario describes automatically adding and removing App Service instances in response to real-time traffic spikes, which is the definition of elasticity. Elasticity is the ability to dynamically scale resources up or down to match demand, ensuring you only pay for what you use. In Azure, this is implemented via autoscale rules that adjust the instance count based on metrics like CPU or request queue length.
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
Correct. Elasticity is the cloud characteristic that enables resources to be automatically added or removed in response to real-time demand, allowing the application to handle traffic spikes and then scale back down to optimize costs.
- ✗
Scalability
Why it's wrong here
Scalability is the ability to increase capacity to handle growing demand, but it does not inherently imply automatic scaling down. Elasticity includes both scaling up and down dynamically, which is the key difference in this scenario.
When this WOULD be correct
A question that asks: 'Which cloud characteristic allows a system to handle growing amounts of work by adding resources in a planned manner, such as adding more servers during a scheduled marketing campaign?' would make scalability correct, as it focuses on the ability to scale up or out without emphasizing automatic reduction.
- ✗
High availability
Why it's wrong here
High availability refers to maximizing uptime and ensuring the application remains reachable despite infrastructure disruptions, often using multiple instances across availability zones and health probes to route around failed nodes. The described scenario involves anticipated or real-time increases in web traffic requiring dynamic capacity changes. High availability does not itself add or remove compute resources based on load; it addresses service continuity, making it distinct from the elasticity being exercised.
When this WOULD be correct
A question asking: 'A company deploys a web app across multiple Azure regions with load balancing and automatic failover. Which cloud characteristic ensures the app remains accessible even if one region fails?' Here, high availability is correct.
- ✗
Fault tolerance
Why it's wrong here
Fault tolerance describes a system's ability to continue operating correctly when one or more components fail, typically achieved through redundant components, failover, and data replication. The scenario describes a web application receiving variable traffic and automatically adjusting resources in response to demand. That load-driven behavior is elasticity, not fault tolerance, because nothing in the scenario mentions component failures or the need to mask such failures.
When this WOULD be correct
A question asking: 'An application runs on multiple VMs across availability zones. If one zone fails, the application continues running without downtime. Which characteristic does this describe?' would make fault tolerance 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
Correct. Elasticity is the cloud characteristic that enables resources to be automatically added or removed in response to real-time demand, allowing the application to handle traffic spikes and then scale back down to optimize costs.
✗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 include the automatic removal of resources when demand decreases. The question specifically describes dynamic provisioning and de-provisioning based on real-time demand, which is the defining characteristic of elasticity.
★ When this WOULD be the correct answer
A question that asks: 'Which cloud characteristic allows a system to handle growing amounts of work by adding resources in a planned manner, such as adding more servers during a scheduled marketing campaign?' would make scalability correct, as it focuses on the ability to scale up or out without emphasizing automatic reduction.
Why candidates choose this
Candidates often confuse scalability with elasticity because both involve resource adjustment. Scalability is a broader term that includes elasticity, but elasticity specifically adds the dimension of automatic, bidirectional scaling based on real-time demand, which is the key nuance in this question.
✗High availabilityWrong answer — click to see why▾
Why this is wrong here
High availability focuses on ensuring the application remains accessible despite failures, not on dynamically adjusting resources to match fluctuating demand. The question describes automatic scaling based on traffic, which is elasticity, not high availability.
★ When this WOULD be the correct answer
A question asking: 'A company deploys a web app across multiple Azure regions with load balancing and automatic failover. Which cloud characteristic ensures the app remains accessible even if one region fails?' Here, high availability is correct.
Why candidates choose this
Candidates may confuse high availability with elasticity because both involve redundancy and scaling, but high availability is about uptime and fault tolerance, not dynamic resource provisioning based on demand.
✗Fault toleranceWrong answer — click to see why▾
Why this is wrong here
Fault tolerance refers to a system's ability to continue operating without interruption in the event of component failures, not to dynamic resource scaling based on demand. The question describes adding/removing instances to match load, which is elasticity.
★ When this WOULD be the correct answer
A question asking: 'An application runs on multiple VMs across availability zones. If one zone fails, the application continues running without downtime. Which characteristic does this describe?' would make fault tolerance correct.
Why candidates choose this
Candidates may confuse fault tolerance with elasticity because both involve handling unexpected conditions, but fault tolerance focuses on failure resilience, not demand-driven 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
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.
Key term
Azure App Service
Azure App Service is a fully managed platform for building, deploying, and scaling web applications and APIs without managing the underlying infrastructure.
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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.