AZ-900 Describe cloud concepts Practice Question
What is the difference between 'high availability' and 'fault tolerance' in cloud computing?
⚠ Common exam trap
Watch out — candidates often confuse high availability with fault tolerance because both involve redundancy, but the key difference is that HA allows brief downtime during failover, while fault tolerance guarantees zero interruption.
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
✓
High availability minimizes downtime during failures; fault tolerance aims for zero interruption despite failures
High availability (HA) focuses on minimizing downtime by using redundant components and failover mechanisms, typically achieving uptime of 99.99% or higher, but it may allow brief interruptions during failover. Fault tolerance, in contrast, is designed to operate without any interruption at all, often through active-active configurations or redundant hardware that masks failures completely. Option B correctly captures this distinction: HA reduces downtime, while fault tolerance aims for zero interruption.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
High availability and fault tolerance are identical concepts
Why it's wrong here
High availability and fault tolerance are related but not identical. High availability minimizes downtime to near zero using redundancy and automated failover, yet a brief service interruption is still possible during the transition. Fault tolerance goes further and aims for zero user-visible interruption by having redundant components operate in parallel so a single failure has no effect. They differ fundamentally in the acceptable recovery time and the level of impact on users.
- ✓
High availability minimizes downtime during failures; fault tolerance aims for zero interruption despite failures
Why this is correct
High availability is designed to keep downtime minimal, typically through automated failover to a standby component, but that failover incurs a short period of unavailability. Fault tolerance is designed to achieve zero interruption: systems are architected with redundant components that process requests in parallel, so the failure of one component does not degrade service at all. In practical terms, high availability might experience a few seconds of outage, while fault tolerance ensures continuous operation with absolutely no user impact during component failures.
- ✗
High availability requires multiple regions; fault tolerance requires only one region
Why it's wrong here
Neither high availability nor fault tolerance requires a specific number of regions. High availability is most often achieved within a single region by using Availability Zones, which are physically separate datacenters with independent power, cooling, and networking. Fault tolerance can also be implemented within one region by deploying active-active redundant components that automatically take over without delay. Adding multiple regions addresses disaster recovery, not the fundamental HA versus FT distinction.
- ✗
Fault tolerance is only for databases; high availability is for compute
Why it's wrong here
Fault tolerance is not limited to databases, nor is high availability limited to compute. Both are architectural principles that apply equally to virtual machines, containers, storage accounts, networking, and serverless services. For example, Azure Virtual Machines use Availability Sets for high availability, while Azure SQL Database offers built-in high availability and even fault-tolerant designs via zone-redundant configurations. The implementation scope depends on the workload, not on the resource type.
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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