AZ-900 Describe Azure architecture and services Practice Question
What is the purpose of Azure Availability Sets?
⚠ Common exam trap
It's easy for candidates to confuse Availability Sets (single-datacenter fault/update domain isolation) with Availability Zones (cross-datacenter resilience) or Virtual Machine Scale Sets (horizontal scaling), leading candidates to pick Option A or C incorrectly.
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
✓
To protect VMs from hardware failures and planned maintenance within a single datacenter
Azure Availability Sets protect VMs from hardware failures and planned maintenance within a single datacenter by grouping VMs into fault domains (to isolate against rack-level failures) and update domains (to sequence planned maintenance reboots). This ensures at least one VM instance remains available during Azure infrastructure updates or unexpected hardware issues.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
To deploy VMs across multiple Azure regions for global availability
Why it's wrong here
Deploying VMs across multiple Azure regions for global availability requires creating separate VM deployments in each target region and configuring a traffic-routing service like Azure Traffic Manager or Front Door to distribute traffic between regions. An Availability Set constrains all its VMs to the same datacenter/region—choosing a region defines its boundary. It is specifically designed for intra-region resilience, not cross-region failover.
- ✓
To protect VMs from hardware failures and planned maintenance within a single datacenter
Why this is correct
An Availability Set distributes VMs across multiple fault domains—physically separate racks with independent power, cooling, and network—and multiple update domains that receive planned maintenance sequentially. This design ensures that an unplanned hardware failure or a maintenance event only impacts a subset of the VMs, preserving workload availability. With at least two VMs in the set, Azure provides a 99.95% uptime SLA within a single datacenter.
- ✗
To automatically scale the number of VMs based on CPU utilization
Why it's wrong here
Automatic scaling based on CPU utilization is performed by Virtual Machine Scale Sets, which can add or remove VM instances using autoscale rules and metrics like CPU percentage. An Availability Set is a purely structural placement mechanism that distributes VMs across fault and update domains; it does not monitor load or adjust instance count. Therefore, scaling is not a function of an Availability Set.
- ✗
To provide dedicated physical servers for a single organization
Why it's wrong here
Dedicated physical servers that are isolated for a single organization are provided by Azure Dedicated Host, where the entire host server is reserved for your VMs. In contrast, VMs in an Availability Set share the same physical infrastructure with other customers' VMs, with only hardware-level fault isolation between racks. For compliance requiring single-tenant isolation, you would deploy on a Dedicated Host, not an Availability Set.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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