SOA-C02 Reliability and Business Continuity Practice Question
A company is running a web application on EC2 instances behind an Application Load Balancer. They want to ensure that if an entire Availability Zone fails, the application remains available. Which configuration should they implement?
⚠ Common exam trap
Many exam-takers confuse high availability at the database layer (RDS Multi-AZ) with compute layer fault tolerance, or they mistakenly believe that scaling vertically (larger instances) or increasing monitoring granularity can compensate for a full AZ outage.
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
✓
Configure the Auto Scaling group to launch instances in multiple Availability Zones.
To ensure application availability during an entire Availability Zone (AZ) failure, the Auto Scaling group must be configured to launch EC2 instances across multiple AZs. This distributes the workload so that if one AZ becomes unavailable, the remaining AZs continue serving traffic. The Application Load Balancer (ALB) automatically routes requests only to healthy instances in the surviving AZs, maintaining application uptime.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Configure the Auto Scaling group to launch instances in multiple Availability Zones.
Why this is correct
Configuring the Auto Scaling group to span multiple Availability Zones is the correct approach because it distributes the EC2 instances across independent failure domains. If one AZ becomes unavailable, the instances in the other AZs continue to serve traffic, and the ASG automatically replaces the unhealthy instances to maintain desired capacity. This architecture provides high availability for the application tier.
- ✗
Use an RDS Multi-AZ deployment for the application.
Why it's wrong here
RDS Multi-AZ deployment enhances database availability by maintaining a synchronous standby replica in another AZ and automatically failing over if the primary DB fails. However, the application itself runs on EC2 instances, and Multi-AZ does nothing to protect those instances from an AZ outage. If all app instances are in a single AZ and that AZ fails, the application tier becomes inaccessible even though the database remains available.
- ✗
Use a larger EC2 instance type.
Why it's wrong here
Using a larger EC2 instance type increases CPU, memory, and network capacity to handle more load or improve performance, but it does not introduce any redundancy. A single instance, regardless of size, is still a single point of failure and will become unavailable if its host hardware or its Availability Zone experiences an outage. The goal is to ensure availability, not just scale up capacity.
- ✗
Enable detailed monitoring on the EC2 instances.
Why it's wrong here
Enabling detailed monitoring changes the CloudWatch metric collection interval to 1 minute and supports finer-grained Auto Scaling and alarms. However, it only provides telemetry data; it does not alter the deployment topology or protect instances against an AZ failure. Detailed monitoring might help detect an issue sooner, but it cannot prevent the application from going down when an entire AZ is lost.
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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.