AZ-305 Design infrastructure solutions Practice Question
A company runs a critical application on Azure VMs in a single region. They need to improve availability to meet an SLA of 99.99% while minimizing costs. The application is stateless and can run on multiple VMs. Which solution should you recommend?
⚠ Common exam trap
The trap here is that candidates often over-engineer by choosing multi-region solutions (Option D) or under-engineer with availability sets (Option B), failing to recognize that a single-region, multi-zone scale set is the optimal balance of cost and availability for a stateless app targeting 99.99%.
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
✓
Deploy a virtual machine scale set across multiple availability zones in a single region.
A virtual machine scale set deployed across multiple availability zones in a single region provides zone-level redundancy, protecting against datacenter failures while keeping traffic within a single region for low latency. This configuration can achieve up to 99.99% availability (when using two or more zones) without the cost and complexity of multi-region replication, making it the most cost-effective solution for a stateless application.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Deploy a virtual machine scale set across multiple availability zones in a single region.
Why this is correct
A virtual machine scale set deployed across multiple availability zones distributes VM instances among distinct fault domains and update domains in separate Azure datacenters within the same region. This architecture meets the 99.99% availability SLA for virtual machines while also enabling elastic scaling and automatic rebalancing of instances, making it a cost-effective and resilient single-region solution. Because all instances reside in the same region, latency remains low and the setup avoids the expense of replicating data across geo-disparate regions.
- ✗
Deploy two VMs in the same availability set in a single region.
Why it's wrong here
An availability set places VMs in separate fault domains and update domains, but it does not guarantee an SLA higher than 99.95% for individual VMs (or 99.95% for a two-VM availability set). Each fault domain in an availability set corresponds to a rack within a single Azure datacenter, not an independent datacenter or power/cooling zone. Therefore, this configuration fails to meet the 99.99% availability target and also provides no protection against an entire datacenter failure.
- ✗
Deploy a single VM with Azure Site Recovery to another region.
Why it's wrong here
Azure Site Recovery replicates a single VM to a secondary region for disaster recovery, but it does not provide continuous high availability within the primary region. The SLAs offered by ASR are tied to recovery time objectives (RPO/RTO) for failover, not to the uptime of the application during normal operations, and a single VM in the primary region still has no availability SLA if the underlying host or datacenter fails. Additionally, ASR failover involves manual or automated steps and incurs replication and DR costs without scaling benefits.
- ✗
Deploy two VMs in two different Azure regions with Azure Traffic Manager.
Why it's wrong here
Deploying two VMs in two different Azure regions with Azure Traffic Manager provides geo-redundancy and can route users to a healthy region, but it does not directly address the need for a 99.99% SLA within a single region. Traffic Manager uses DNS-level routing and has a failover time that depends on DNS TTL and health probe intervals, so it is not a zero-downtime high-availability solution inside a region. This design also introduces significant extra cost, data-residency considerations, and management complexity that a single-region zonal architecture avoids.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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