The correct answer is to deploy an Application Load Balancer across multiple Availability Zones, move session storage to ElastiCache, and use an Auto Scaling group. This design achieves high availability for a stateful web application without code changes by externalizing the session state from the EC2 instance to a dedicated, highly available caching layer. By storing user sessions in ElastiCache, the application becomes effectively stateless at the instance level, allowing any healthy instance in the Auto Scaling group to handle any request, while the Application Load Balancer distributes traffic across zones. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this scenario tests your understanding that true high availability requires decoupling state from compute; a common trap is assuming sticky sessions or Route 53 health checks alone solve the problem, but they still tie sessions to a single instance. Remember the memory tip: "State out, scale in" — externalize the state to ElastiCache, then scale instances freely with Auto Scaling.
SOA-C02 Reliability and Business Continuity Practice Question
This SOA-C02 practice question tests your understanding of reliability and business continuity. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company is running a stateful web application on a single EC2 instance in a public subnet. The instance stores user sessions locally. The company wants to improve availability without rewriting the application. Which design should they use?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Deploy an Application Load Balancer across multiple AZs, move session storage to ElastiCache, and use an Auto Scaling group.
Option B is correct because using Network Load Balancer with target groups across AZs and storing sessions in ElastiCache allows statelessness and high availability without code changes. Option A is wrong because Route 53 health checks alone do not handle session state. Option C is wrong because an Application Load Balancer with sticky sessions still ties sessions to instances. Option D is wrong because an Auto Scaling group without session externalization will lose sessions.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Create a second EC2 instance in a different AZ and use Route 53 with health checks.
Why it's wrong here
Route 53 does not provide load balancing for session state.
✗
Use an Auto Scaling group across multiple AZs but keep sessions on instance.
Why it's wrong here
Sessions lost if instance is terminated.
✓
Deploy an Application Load Balancer across multiple AZs, move session storage to ElastiCache, and use an Auto Scaling group.
Why this is correct
ElastiCache externalizes session state; ALB and Auto Scaling provide high availability.
Use an Application Load Balancer with sticky sessions and an Auto Scaling group in a single AZ.
Why it's wrong here
Sticky sessions still tie to instances; single AZ is a failure point.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related SOA-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Reliability and Business Continuity — This question tests Reliability and Business Continuity — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Deploy an Application Load Balancer across multiple AZs, move session storage to ElastiCache, and use an Auto Scaling group. — Option B is correct because using Network Load Balancer with target groups across AZs and storing sessions in ElastiCache allows statelessness and high availability without code changes. Option A is wrong because Route 53 health checks alone do not handle session state. Option C is wrong because an Application Load Balancer with sticky sessions still ties sessions to instances. Option D is wrong because an Auto Scaling group without session externalization will lose sessions.
What should I do if I get this SOA-C02 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related SOA-C02 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company runs a stateful web application on a single EC2 instance. To improve reliability, the company wants to implement a highly available architecture. What should the SysOps administrator do?
medium
✓ A.Refactor the application to store session state externally (e.g., ElastiCache), then deploy it across multiple AZs with an Application Load Balancer.
B.Migrate the application to a larger instance type.
C.Create a standby EC2 instance and use an Elastic IP to fail over manually.
D.Use Route 53 health checks to route traffic to a secondary instance if the primary fails.
Why A: Option C is correct because making the application stateless and distributing instances across multiple AZs with a load balancer provides high availability. Option A is wrong because a larger instance is still a single point of failure. Option B is wrong because a standby instance is not automatically used; failover is manual. Option D is wrong because Route 53 health checks alone do not handle failover automatically if the instance is stateful.
Last reviewed: Jun 20, 2026
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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.
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