SOA-C02 Reliability and Business Continuity Practice Question
A company runs a critical web application on EC2 instances behind an Application Load Balancer in a single Availability Zone. To improve reliability, what is the MOST effective design change?
⚠ Common exam trap
The trap here is that candidates often focus on scaling or database redundancy (options A and C) instead of recognizing that the fundamental reliability gap is the single Availability Zone, which requires distributing compute resources across multiple AZs to achieve true high availability.
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
✓
Launch EC2 instances across two or more Availability Zones.
The most effective design change to improve reliability is to launch EC2 instances across two or more Availability Zones. This eliminates the single point of failure at the Availability Zone level, ensuring that if one AZ experiences an outage, the Application Load Balancer can route traffic to healthy instances in another AZ. This directly addresses the core reliability principle of fault isolation and high availability.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Place the RDS database in a Multi-AZ deployment.
Why it's wrong here
Placing RDS in a Multi-AZ deployment protects only the database tier by maintaining a synchronously replicated standby in a separate Availability Zone and enabling automatic failover. The critical web application's EC2 compute layer remains a single point of failure: if the AZ hosting those instances goes down, there is no application server to process requests even though the database is still available. This option does not address the stated need to make the web tier itself resilient to an AZ failure.
- ✗
Add a second Application Load Balancer in the same Availability Zone.
Why it's wrong here
An Application Load Balancer is already a regional service that can distribute traffic across multiple AZs when subnets are enabled in them. Adding a second ALB in the same Availability Zone does not create a new failure domain; both load balancers and any instances in that AZ will fail together during an AZ outage. This configuration provides redundant components within the same fault domain rather than eliminating the AZ-level single point of failure, so it cannot make the web application highly available.
- ✗
Increase the EC2 instance size to handle more traffic.
Why it's wrong here
Increasing the EC2 instance size (vertical scaling) gives the application more CPU and memory to handle higher traffic, but it does not add any redundancy or fault tolerance. If the instance is in a single Availability Zone and that AZ experiences an outage, the larger instance is still unavailable, and the critical workload goes down. High availability requires multiple independent instances across AZs, not simply a bigger single instance, so this change does not protect against AZ failure.
- ✓
Launch EC2 instances across two or more Availability Zones.
Why this is correct
Launching EC2 instances across two or more Availability Zones eliminates the AZ as a single point of failure for the compute tier. When used with an Application Load Balancer (or other load balancing) and ideally an Auto Scaling group, traffic can be distributed to healthy instances in the remaining AZs even if one entire AZ fails. This is the core architectural pattern for building a highly available web application on AWS.
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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.