AZ-305 Design infrastructure solutions Practice Question
You are designing a disaster recovery solution for a multi-tier application. The application consists of a web tier, an application tier, and a database tier running SQL Server on Azure VMs. The RPO must be 5 seconds, and the RTO must be 15 minutes. You need to recommend a SQL Server availability solution that meets these requirements. What should you use?
⚠ Common exam trap
Watch out — candidates often confuse Azure Site Recovery's VM-level replication with database-level replication, overlooking that ASR's RPO/RTO are typically higher and not suitable for sub-minute RPO requirements, while log shipping is dismissed due to its manual failover and higher RPO.
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
✓
SQL Server Always On Availability Groups with synchronous commit and automatic failover
SQL Server Always On Availability Groups with synchronous commit and automatic failover provides near-zero data loss (RPO of 5 seconds) and rapid automatic failover (RTO of 15 minutes) by replicating data synchronously across replicas. This solution meets the stringent RPO/RTO requirements for a multi-tier application running SQL Server on Azure VMs, as it ensures transactions are committed on both primary and secondary replicas before acknowledging success, and automatic failover occurs within seconds if the primary fails.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Azure SQL Database Managed Instance automatic backups
Why it's wrong here
Managed Instance automatic backups are service-controlled backups taken periodically; the point-in-time restore feature offers an RPO of up to 5 minutes, not 5 seconds. Restoring a database also requires re-provisioning and replaying transaction logs, resulting in an RTO that typically exceeds 15 minutes. Therefore, this option fails the required 5-second RPO and the strict RTO requirement.
- ✗
Azure Site Recovery with replication of SQL Server VMs
Why it's wrong here
Azure Site Recovery replicates whole VMs at the disk level using snapshots and change replication, but it does not understand SQL Server transaction log semantics. The replication frequency and snapshot cadence yield a best-case RPO of several minutes, not 5 seconds, and failover involves booting the VM and running SQL recovery, which pushes RTO beyond 15 minutes. Thus it is not suitable for a database-aware DR solution with near-zero data loss.
- ✗
SQL Server log shipping
Why it's wrong here
SQL Server log shipping relies on a recurring cycle of backing up the transaction log, copying that backup to the secondary server, and restoring it. To achieve an RPO of 5 seconds you would need to run that entire cycle every 5 seconds, which is operationally impractical and does not meet the typical design. Even with frequent log backups, the RTO includes the final restore and recovery of the database, often exceeding the 15-minute limit for large databases.
- ✓
SQL Server Always On Availability Groups with synchronous commit and automatic failover
Why this is correct
SQL Server Always On Availability Groups with synchronous commit mode writes the transaction to the primary and at least one secondary replica before acknowledging the commit, guaranteeing zero data loss and an RPO of 0 seconds. Automatic failover, when configured with two synchronous replicas and a quorum of validators, can complete in seconds to a few minutes, comfortably meeting the RTO of under 15 minutes. This is the only option that satisfies both the 5-second RPO and 15-minute RTO requirements.
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Related to this question
Learn chapter
Designing Compute Solutions
Key term
BIA and RPO RTO Design
Business Impact Analysis and the design of Recovery Point Objective and Recovery Time Objective define how much data loss and downtime a business can tolerate after an IT failure, guiding the architecture of backup and disaster recovery systems.
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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