AZ-305 Design business continuity solutions Practice Question
A company uses Azure Cosmos DB with a single write region. They need to ensure business continuity with an RPO of 5 seconds and RTO of 1 minute in case of a regional outage. What configuration should they use?
⚠ Common exam trap
It's easy for candidates to assume automatic failover from a single write region is sufficient, but they overlook that the default replication lag guarantee is 5 minutes, which fails the strict RPO requirement, and that multi-region writes are the only way to achieve sub-minute RTO and near-zero RPO for regional outages.
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
✓
Enable multi-region writes with automatic failover
Multi-region writes with automatic failover allows any Azure Cosmos DB region to accept writes, and if the primary region fails, the SDK automatically routes write requests to the next nearest region. This configuration can achieve an RPO of 0 (no data loss) and an RTO of less than a minute, which exceeds the required RPO of 5 seconds and RTO of 1 minute. The key is that with multi-region writes, there is no need to promote a read region to a write region, eliminating the failover delay and potential data loss.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Enable multi-region writes with automatic failover
Why this is correct
Enabling multi-region writes with automatic failover makes every participating region a writable replica, so writes can be served by any region and replicated asynchronously with conflict resolution based on LSNs. Because no region is a passive secondary that must be promoted, automatic failover simply redirects traffic without waiting for data catch-up, achieving an RPO of 0 and an RTO of seconds. This is the only option that fully satisfies the requirement for near-zero data loss and automatic cross-region failover.
- ✗
Enable automatic failover from a single write region to a read region
Why it's wrong here
With a single write region, enabling automatic failover designates one read-only region to become the new write region if the primary fails, but replication between regions is asynchronous. Therefore the promoted region can be up to 15 minutes behind, meaning committed writes may be lost, so the effective RPO is not zero. The failover process also involves detection, health probes, and DNS update, which adds RTO delay; this option addresses availability but not the requirement of zero data loss.
- ✗
Deploy Cosmos DB in an availability zone-enabled region
Why it's wrong here
Availability-zone-enabled Cosmos DB replicates data synchronously across multiple zones within a single Azure region, protecting against rack or datacenter failures but providing no cross-region redundancy. Because all zones are part of the same regional footprint, a regional outage takes down the entire deployment, making failover impossible. This option is about high availability within a region, not the cross-region disaster recovery and failover behavior the scenario requires.
- ✗
Use manual failover to a secondary read region
Why it's wrong here
A manual failover to a secondary read region requires an operator to trigger the promotion after a failure is detected, and the process includes waiting for the read region to catch up and updating the connection endpoint via DNS. Because the original write region may be unavailable and the secondary has asynchronous replication, some committed writes could be missing, giving an RPO of up to 15 minutes. The human-in-the-loop action also drives RTO to minutes or hours, which fails the requirement for automatic, near-zero data loss failover.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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