AZ-900 Describe cloud concepts Practice Question
A company deploys a mission-critical application across three Azure availability zones. The application is designed to continue operating without any interruption if an entire availability zone becomes unavailable. Which cloud computing characteristic does this scenario best illustrate?
⚠ Common exam trap
Many candidates confuse high availability with fault tolerance, but high availability allows for brief downtime during failover (e.g., 99.99% uptime), while fault tolerance guarantees zero interruption even during a complete zone failure.
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
✓
Fault tolerance
B is correct because fault tolerance is the ability of a system to continue operating without any interruption when a component fails. Deploying a mission-critical application across three Azure availability zones ensures that if an entire zone goes down, the application remains operational with zero downtime, which is the defining characteristic of fault tolerance.
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 it's wrong here
Elasticity is the automatic, real-time adjustment of resource capacity in response to changing demand, often implemented with Azure Autoscale or virtual machine scale sets. While elasticity helps maintain performance during load spikes, it does not provide inherent resilience to zone-level failures unless instances are deliberately distributed across zones. The application's requirement to run 'without any interruption' when an availability zone fails demonstrates fault tolerance, not the demand-driven scaling that elasticity describes.
When this WOULD be correct
A company deploys an application that automatically adds virtual machines during peak traffic and removes them when demand decreases. Which cloud characteristic does this best illustrate?
- ✓
Fault tolerance
Why this is correct
Fault tolerance means a system can continue operating correctly even when a component fails, here exemplified by an entire availability zone disappearing without causing any interruption to the application. This is typically achieved through redundancy—running duplicate workloads across separate zones with active-active traffic routing and data replication. In Azure, an availability zone failure triggers automatic failover between replicas with zero downtime, which is the hallmark of fault tolerance.
- ✗
High availability
Why it's wrong here
High availability focuses on minimizing downtime but typically allows for a short period of unavailability during failover (e.g., seconds to minutes). The scenario specifies 'without any interruption,' which is a stricter requirement more aligned with fault tolerance.
When this WOULD be correct
This option would be correct in a scenario describing an application that uses multiple VMs in an availability set or across zones to ensure it remains accessible with minimal downtime (e.g., 99.99% uptime) but may experience brief interruptions during failover.
- ✗
Scalability
Why it's wrong here
Scalability is about a system's ability to handle growing or shrinking workloads by adding or removing resources, such as scaling out virtual machines or scaling up a database tier. It does not address what happens when a component fails; a highly scalable application can still be completely unavailable if its sole deployment region experiences an outage. The given scenario specifies continuous operation during an availability zone failure, which requires architectural redundancy rather than simply the capacity to expand.
When this WOULD be correct
A web application experiences sudden traffic spikes during a product launch. The company automatically adds virtual machines to handle the load and removes them when traffic subsides. This scenario best illustrates scalability.
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.
✓Fault toleranceCorrect answer▾
Why this is correct
Fault tolerance means a system can continue operating correctly even when a component fails, here exemplified by an entire availability zone disappearing without causing any interruption to the application. This is typically achieved through redundancy—running duplicate workloads across separate zones with active-active traffic routing and data replication. In Azure, an availability zone failure triggers automatic failover between replicas with zero downtime, which is the hallmark of fault tolerance.
✗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 to maintain operation during a zone failure. The scenario describes fault tolerance, which ensures continuous operation despite component failures.
★ When this WOULD be the correct answer
A company deploys an application that automatically adds virtual machines during peak traffic and removes them when demand decreases. Which cloud characteristic does this best illustrate?
Why candidates choose this
Candidates may confuse fault tolerance with elasticity because both involve handling changes, but elasticity focuses on scaling resources, not surviving failures.
✗High availabilityWrong answer — click to see why▾
Why this is wrong here
High availability focuses on minimizing downtime through redundancy and failover, but the scenario explicitly states the application continues operating without any interruption during a zone failure, which is fault tolerance—the ability to maintain functionality despite component failures.
★ When this WOULD be the correct answer
This option would be correct in a scenario describing an application that uses multiple VMs in an availability set or across zones to ensure it remains accessible with minimal downtime (e.g., 99.99% uptime) but may experience brief interruptions during failover.
Why candidates choose this
Candidates often confuse high availability with fault tolerance because both involve redundancy; however, high availability aims to reduce downtime, while fault tolerance ensures zero interruption, a subtle but critical distinction.
✗ScalabilityWrong answer — click to see why▾
Why this is wrong here
Scalability refers to the ability to increase or decrease resources to meet demand, not to maintain operation during failures. The scenario describes fault tolerance, which ensures continuous operation despite component failures.
★ When this WOULD be the correct answer
A web application experiences sudden traffic spikes during a product launch. The company automatically adds virtual machines to handle the load and removes them when traffic subsides. This scenario best illustrates scalability.
Why candidates choose this
Candidates may confuse scalability with fault tolerance because both involve handling increased load or failures, but scalability focuses on resource adjustment for demand, not on maintaining uptime during failures.
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
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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