SOA-C02 Reliability and Business Continuity Practice Question
A company is running a critical web application on EC2 instances behind an Application Load Balancer. The instances are in an Auto Scaling group across two Availability Zones. The company needs to ensure that if an entire Availability Zone fails, the application remains available. Which configuration meets this requirement?
⚠ Common exam trap
Test-takers frequently confuse scaling (increasing instance size or count) with high availability (distributing across AZs), leading them to choose Option A or C, or they mistakenly think CloudFront provides regional failover for dynamic web applications, which it does not by default.
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 at least two Availability Zones.
Configuring the Auto Scaling group to launch instances in at least two Availability Zones ensures that if one AZ fails, the remaining AZ(s) continue to serve traffic. The Application Load Balancer automatically distributes incoming requests across healthy instances in all configured AZs, and the Auto Scaling group replaces failed instances in the remaining AZs, maintaining capacity. This design provides high availability without relying on a single AZ, which would be a single point of 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.
- ✗
Use larger EC2 instance types to handle the load during a failure.
Why it's wrong here
Scaling vertically by selecting larger EC2 instance types (e.g., moving from t3.large to m5.4xlarge) increases compute capacity but does not address availability zone (AZ) failures. If the entire AZ goes down, all instances of that type in that AZ become unavailable, regardless of their size. To achieve fault tolerance, you need redundant instances spread across multiple AZs, not just bigger machines.
- ✗
Use Amazon CloudFront to distribute traffic across multiple regions.
Why it's wrong here
Amazon CloudFront is a content delivery network (CDN) that caches and serves static and dynamic content from edge locations to reduce latency and offload origin traffic. It does not provide automatic failover for your EC2 instances or route traffic across AZs; if the origin is unreachable, CloudFront continues to point to the same unhealthy endpoint. While it can distribute requests globally, it is not a substitute for an Auto Scaling group configured across multiple AZs for high availability.
- ✗
Launch all instances in the same Availability Zone to reduce latency.
Why it's wrong here
Colocating all instances in a single Availability Zone minimizes inter‑instance latency but creates a single point of failure. If that AZ experiences an outage or network disruption, the entire application becomes unavailable. Multi‑AZ deployments typically add only milliseconds of latency between AZs, which is far outweighed by the criticality of maintaining availability during an AZ failure.
- ✓
Configure the Auto Scaling group to launch instances in at least two Availability Zones.
Why this is correct
Configuring the Auto Scaling group to launch instances in at least two Availability Zones is the correct approach. The Auto Scaling group automatically distributes instances across the selected AZs, and if one AZ fails, the remaining instances continue to operate and serve traffic. Additionally, Auto Scaling can replace unhealthy instances in other AZs, and when combined with an Application Load Balancer, it ensures cross‑AZ load balancing and resilient failover.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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