SOA-C02 Reliability and Business Continuity Practice Question
Which TWO actions improve the availability of an application running on EC2 instances in a single Auto Scaling group? (Choose 2)
⚠ Common exam trap
Candidates often confuse scaling actions (like increasing instance size) or monitoring (like CloudWatch alarms) with direct availability improvements, failing to recognize that only redundancy (multiple AZs) and health-based traffic routing (ELB health checks) actively mitigate failures.
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
✓
Use an Elastic Load Balancer with health checks to route traffic only to healthy instances.
An Elastic Load Balancer (ELB) performs health checks against EC2 instances and automatically routes traffic only to instances that pass those checks. If an instance becomes unhealthy, the ELB stops sending traffic to it, preventing user requests from reaching a failing instance and thereby improving application 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.
- ✓
Use an Elastic Load Balancer with health checks to route traffic only to healthy instances.
Why this is correct
An Elastic Load Balancer continuously performs health checks against targets in its target group, using protocols like HTTP or TCP. If an instance fails a configured number of consecutive checks, the ELB automatically marks it unhealthy and stops routing traffic to it, while continuing to send requests only to healthy instances. This provides built-in fault tolerance for instance failures and is essential for maintaining application availability.
- ✗
Increase the instance size to handle higher load.
Why it's wrong here
Resizing to a larger instance type (scale up) increases CPU, memory, and network capacity for a single EC2 instance, but it does nothing to provide redundancy or failover. The instance remains a single point of failure—if the underlying host, network, or Availability Zone has an outage, the application goes down. Availability depends on having multiple replaceable components, not simply on a more powerful server.
- ✗
Create a CloudWatch alarm to notify when the CPU utilization exceeds 80%.
Why it's wrong here
A CloudWatch alarm that fires when CPU utilization exceeds 80% can send an SNS notification to operators, but that only creates awareness. Without being coupled to a scaling policy or a remediation action in an Auto Scaling group, the alarm does not add or remove instances, so it has no direct effect on the application's ability to serve traffic. Notification is useful for reaction, but it does not automatically improve availability.
- ✗
Enable EBS optimization on the instances.
Why it's wrong here
EBS optimization is an instance feature that provides dedicated throughput between the instance and its attached EBS volumes, reducing contention and improving I/O performance. It is purely a performance enhancement for storage operations; it does not introduce redundancy, failover, or health detection. Therefore, enabling EBS optimization cannot prevent downtime caused by instance termination, AZ outage, or application failure.
- ✓
Configure the Auto Scaling group to launch instances in multiple Availability Zones.
Why this is correct
Launching instances in multiple Availability Zones within an Auto Scaling group means the ASG can maintain capacity even when an entire AZ becomes unavailable, because the remaining AZs still contain healthy instances. The ASG also uses health checks to replace failed instances, but distributing across AZs is what gives resilience to a zone-level failure. Combined with an ELB, traffic can be balanced across the AZs, making the application highly available.
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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.