SOA-C02 Reliability and Business Continuity Practice Question
A company is designing a highly available architecture for a web application using AWS services. Which TWO actions should the SysOps administrator take to improve reliability? (Choose TWO.)
⚠ Common exam trap
Candidates often think a single large instance is simpler and more reliable, but AWS explicitly recommends horizontal scaling with multiple instances across Availability Zones to eliminate single points of failure.
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 Auto Scaling group with an Elastic Load Balancer.
An Auto Scaling group combined with an Elastic Load Balancer automatically distributes incoming traffic across healthy EC2 instances and replaces any failed instances, ensuring the application remains available even during instance failures or traffic spikes. This architecture is a core AWS best practice for building highly available and resilient web applications.
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 a single large EC2 instance to eliminate complexity.
Why it's wrong here
A single large EC2 instance, regardless of size, creates a single point of failure; if the underlying host fails or the instance is stopped for maintenance, the application becomes unavailable. It also lacks elasticity because you cannot scale out during load spikes, and scaling up requires a stop/start action that causes downtime. This approach abandons the automated recovery and health-check features that an Auto Scaling group provides.
- ✓
Use an Auto Scaling group with an Elastic Load Balancer.
Why this is correct
An Auto Scaling group combined with an Elastic Load Balancer delivers high availability by maintaining a desired instance count across healthy capacity and automatically replacing failed instances based on health checks. The ELB distributes incoming traffic across all healthy instances, preventing any single node from being overwhelmed and allowing the fleet to scale in and out with demand. When integrated across multiple Availability Zones, this pattern provides both elasticity and fault tolerance, making it a core AWS high-availability design.
- ✗
Use a single NAT gateway for outbound traffic.
Why it's wrong here
A single NAT gateway is an Availability Zone-scoped resource; if that Availability Zone fails, all instances in every AZ lose outbound internet connectivity, breaking updates, API calls, and user-facing features that require egress traffic. Even while operational, the NAT gateway has its own bandwidth and connection limits, and it provides no automatic failover to another gateway. The correct HA pattern is to place one NAT gateway in each AZ and route instances to the gateway within their own AZ, ensuring no single gateway is a point of failure.
- ✓
Deploy EC2 instances in multiple Availability Zones.
Why this is correct
Deploying EC2 instances in multiple Availability Zones protects against an entire data center failure, but this action alone is not a complete high-availability architecture. Without an Auto Scaling group, a failed instance in one AZ will not be automatically replaced, and without a load balancer, traffic cannot be automatically shifted away from unhealthy instances to healthy ones. This is a necessary building block because it provides AZ-level redundancy, but it must be combined with ASG/ELB to achieve real fault tolerance.
- ✗
Store application data on a single EBS volume.
Why it's wrong here
Storing application data on a single EBS volume ties that data to one Availability Zone and one EC2 instance. If the instance fails, the volume can be detached and re-attached to a replacement instance, but the delay causes significant downtime, and the volume remains a single point of failure for the data. A single EBS volume also cannot be attached to multiple instances for concurrent access, and its IOPS/throughput limits cap application scalability. For HA, use a shared or replicated storage layer such as EFS, S3, or a multi-AZ database.
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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.