SOA-C02 Reliability and Business Continuity Practice Question
A company hosts a critical web application on Amazon EC2 instances in a single AWS Region (us-east-1). The SysOps administrator needs to implement a Disaster Recovery (DR) solution using a different AWS Region (us-west-2). The DR plan requires a Recovery Time Objective (RTO) of 1 hour and a Recovery Point Objective (RPO) of 15 minutes. The application uses an Amazon Aurora MySQL DB cluster and static assets stored in an Amazon S3 bucket. Which combination of actions should the administrator take to meet these requirements?
⚠ Common exam trap
Test-takers frequently confuse Multi-AZ (which provides high availability within a single region) with cross-region disaster recovery, or they assume manual snapshots and DMS are simpler alternatives without considering the RPO/RTO constraints and operational overhead.
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
✓
Create an Aurora cross-Region read replica in us-west-2. Configure S3 Cross-Region Replication from the source bucket to a destination bucket in us-west-2. During DR, promote the read replica to a primary cluster and update DNS.
Aurora cross-Region read replicas provide asynchronous replication with an RPO typically under 1 second, easily meeting the 15-minute RPO requirement. Promoting the read replica to a primary cluster in us-west-2 can be completed within minutes, satisfying the 1-hour RTO. S3 Cross-Region Replication (CRR) automatically replicates static assets to the destination bucket in us-west-2 with near-real-time latency, ensuring the S3 data is also current within the RPO window.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Create an Aurora cross-Region read replica in us-west-2. Configure S3 Cross-Region Replication from the source bucket to a destination bucket in us-west-2. During DR, promote the read replica to a primary cluster and update DNS.
Why this is correct
A cross-Region read replica provides continuous replication for the database, achieving RPO seconds. Promoting it can be done in minutes, meeting RTO of 1 hour. S3 CRR replicates objects asynchronously, typically within minutes, satisfying the RPO.
- ✗
Take a manual snapshot of the Aurora DB cluster every 15 minutes and copy it to us-west-2. Use S3 batch operations to copy assets to us-west-2 daily.
Why it's wrong here
Manual snapshots of an Aurora cluster are not designed for 15-minute intervals; each snapshot adds storage cost, consumes cluster I/O, and can take several minutes just to create, so a true 15-minute RPO is not guaranteed. The snapshot must then be copied to us-west-2 before it can be restored, and that copy process is asynchronous and non-deterministic in duration, extending the effective RPO beyond 15 minutes and the RTO beyond one hour due to manual restore/promotion steps. For S3, using Batch Operations to copy assets daily introduces up to 24 hours of data loss, completely missing the RPO; S3 Cross-Region Replication would replicate new objects within minutes and is the correct service.
- ✗
Enable Aurora Multi-AZ in us-east-1 and configure S3 transfer acceleration to us-west-2.
Why it's wrong here
Enabling Multi-AZ on the Aurora cluster creates a synchronous standby in a different Availability Zone within us-east-1, but that standby remains in the same region and cannot serve traffic if the entire region fails; Multi-AZ is a high-availability feature, not a disaster recovery mechanism. S3 Transfer Acceleration only speeds up uploads to a single bucket through AWS edge locations; it does not copy existing objects from the source bucket to a bucket in us-west-2, so it provides zero cross-region data replication. Thus, this combination gives no automatic failover capability and fails both the RPO and RTO requirements for a region-wide disaster.
- ✗
Use AWS Database Migration Service (DMS) for continuous replication to a DB instance in us-west-2. Use S3 versioning to keep previous object versions.
Why it's wrong here
AWS Database Migration Service (DMS) is not the most suitable solution for replicating an Amazon Aurora MySQL cluster to another Aurora cluster cross-region, as Aurora offers native, highly efficient cross-region replication with lower RPO/RTO capabilities. DMS is primarily designed for heterogeneous database migrations or specific change data capture needs. Furthermore, S3 versioning only preserves object versions within the same region; it does not facilitate cross-region replication required for disaster recovery. For S3, Cross-Region Replication is the appropriate mechanism.
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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