AZ-305 Design infrastructure solutions Practice Question
Your company has a critical application running on Azure Virtual Machines that processes financial transactions. You need to ensure that the application remains available during an Azure region failure. The application is stateless and can scale horizontally. What is the most cost-effective design to meet the availability requirement?
⚠ Common exam trap
Many candidates assume active-active across regions is always the best for high availability, but the question specifically asks for the most cost-effective design, and Azure Site Recovery with a single-region primary and DR replication is cheaper than maintaining dual-region active-active compute.
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 VMs in an availability zone in the primary region and use Azure Site Recovery to replicate to a secondary region.
Deploying VMs across availability zones within a region protects against datacenter-level failures, but for region-level failures, Azure Site Recovery (ASR) provides cost-effective disaster recovery by replicating VMs to a secondary region. Since the application is stateless and horizontally scalable, you can run a minimal footprint in the primary region and use ASR for orchestrated failover, avoiding the cost of always-on active-active infrastructure.
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 VMs in an active-active configuration across two Azure regions using Traffic Manager and Azure Front Door.
Why it's wrong here
Running active-active with Traffic Manager and Azure Front Door distributes traffic across two fully redundant regional deployments, which is overengineered and expensive for a stateless application because you pay for duplicate compute and storage capacity in both regions at all times. Traffic Manager and Front Door provide global DNS and anycast load balancing with health probing, but they do not by themselves manage VM-level replication or data synchronization, so you must add complex database replication and session affinity handling. For a critical stateless app that only needs to survive a regional outage, an active-passive pattern with Azure Site Recovery is far more cost-effective and simpler to operate.
- ✓
Deploy VMs in an availability zone in the primary region and use Azure Site Recovery to replicate to a secondary region.
Why this is correct
This design places VMs in an availability zone in the primary region to guard against datacenter-level failures, while Azure Site Recovery (ASR) continuously replicates the VMs to a secondary region using asynchronous disk replication. ASR enables an orchestrated, controlled failover to the secondary region when the entire primary region becomes unavailable, and because the secondary resources are only started during failover (or remain deallocated), you avoid paying for idle compute capacity in the passive region. This active-passive approach provides both zone-level and region-level resilience, making it the optimal cost-availability balance for a critical stateless application.
- ✗
Deploy VMs in an availability set in the primary region and use Azure Site Recovery to failover to a secondary region.
Why it's wrong here
Deploying VMs in an availability set protects against within-datacenter failures, such as a rack or network switch failure, by distributing instances across fault and update domains, but all VMs in an availability set remain within a single availability zone. Azure Site Recovery would still replicate to a secondary region, but the primary region's internal availability is weaker: if that entire zone fails, you are forced into a full regional failover even for an issue that could have been contained with zone redundancy. Availability zones offer stronger high-availability within a region, so this combination is inferior to using an availability zone for the primary deployment alongside ASR.
- ✗
Deploy VMs in a single region using Virtual Machine Scale Sets with automatic scaling.
Why it's wrong here
Deploying VMs in a single region with Virtual Machine Scale Sets and automatic scaling provides horizontal elasticity within that one region, but offers no protection against a complete Azure region failure because all instances remain in the same fault domain boundary. This option is tempting because automatic scaling and scale sets are the correct mechanism for handling variable load in a stateless application, and would be the right choice if the requirement were only to survive a single VM or availability-zone failure rather than an entire regional outage.
Go deeper
Related to this question
Learn chapter
Multi-Region Active-Active Architecture
Key term
Disaster Recovery Design
Disaster Recovery Design is the process of planning and implementing strategies to restore IT systems and data after a catastrophic failure, ensuring business continuity with minimal downtime and data loss.
Key term
Azure Site Recovery
Azure Site Recovery is a Microsoft Azure service that keeps your business applications and data running by automatically replicating them to a secondary location and failing over if the primary site goes down.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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