SOA-C02 Reliability and Business Continuity Practice Question
A company has a production AWS account with a single VPC and multiple subnets across two Availability Zones. The company hosts a web application on EC2 instances in an Auto Scaling group. The application uses an Amazon Aurora MySQL database cluster with one writer and two reader instances in the same VPC. The SysOps administrator configured AWS CloudTrail to log API calls and Amazon CloudWatch alarms for operational monitoring. After a recent network partition event in one Availability Zone, the application became unavailable for several minutes. The administrator wants to improve the application's resilience to such events without changing the database cluster configuration. The administrator has budget for additional resources but wants to minimize costs. What should the administrator do?
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
✓
Ensure the Auto Scaling group launches instances in both Availability Zones. Configure the Application Load Balancer to be cross-zone load balancing enabled.
Distributing EC2 instances across both Availability Zones and enabling cross-zone load balancing on the ALB ensures that traffic is routed to healthy instances in any AZ, providing high availability for the application tier during an AZ failure without changing the database cluster. Option A is incorrect because Multi-AZ for Aurora is already inherent; increasing instance size does not improve resilience. Option B is incorrect because a cross-region read replica does not help with within-region AZ failures and adds cost and complexity. Option C is incorrect because creating a second VPC in another region with a separate cluster is expensive and unnecessary for an AZ-level failure.
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-AZ for the Aurora cluster, which is already enabled by default. Additionally, increase the instance size of the writer instance.
Why it's wrong here
Multi-AZ is not a configurable option for Aurora because Aurora is inherently highly available, storing six copies of data across three AZs and automatically failing over the primary instance. Increasing the instance size only scales compute resources and does not add redundant capacity or availability. The scenario's vulnerability likely lies in the EC2 application tier being in a single AZ, which this option completely ignores.
- ✗
Configure a cross-region read replica for the Aurora cluster and promote it to primary if the primary AZ fails.
Why it's wrong here
A cross-region read replica is intended for disaster recovery across AWS Regions and uses asynchronous replication, which can result in replication lag and potential data loss if promoted. For an Availability Zone failure within the same region, promoting a cross-region replica is unnecessary and may redirect traffic to a distant region, increasing latency and cost. It also fails to address the application instances, which remain in the original region and may be unreachable.
- ✗
Create a second VPC in a different AWS Region and set up a second Aurora cluster. Use Route 53 with failover routing to direct traffic to the secondary region if the primary fails.
Why it's wrong here
Although this approach provides full disaster recovery, it is grossly overengineered for a single Availability Zone failure. It requires creating a second VPC, provisioning a second Aurora cluster, maintaining cross-region replication, and implementing Route 53 failover routing, all of which add significant cost and operational complexity. Since AWS Regions contain multiple AZs, you can achieve high availability for an AZ outage simply by launching resources in multiple AZs within the same VPC and region.
- ✓
Ensure the Auto Scaling group launches instances in both Availability Zones. Configure the Application Load Balancer to be cross-zone load balancing enabled.
Why this is correct
An Auto Scaling group configured to launch instances across two Availability Zones automatically replaces any failed instances, including when an entire AZ becomes unhealthy. With cross-zone load balancing enabled on the Application Load Balancer, traffic is distributed evenly across all healthy targets in both AZs, and the ALB will immediately route all traffic to the remaining AZ if the other is impaired. Because the ALB is a regional service, it continues to operate independently of any single AZ failure.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SOA-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SOA-C02 exam.