SOA-C02 Reliability and Business Continuity Practice Question
A company runs a web application on Amazon EC2 instances in an Auto Scaling group. The application stores session state locally on each instance, so users lose their sessions when an instance is replaced. The SysOps administrator needs to make the application stateless so that instances can be replaced without disrupting users. Which action should the administrator take?
⚠ Common exam trap
The trap here is thinking that sticky sessions solve session loss, when they only delay the problem until the bound instance is replaced or fails.
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
✓
Store session state in an Amazon ElastiCache for Redis cluster.
Moving session state to a centralized, highly available store such as ElastiCache for Redis decouples the application from individual instances. Any instance can then serve any user, so instance replacement or scaling does not cause session loss. This is the standard approach to making a stateful web application stateless in a dynamic Auto Scaling environment.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Configure the Auto Scaling group to use a termination policy that terminates the oldest instance.
Why it's wrong here
Changing the termination policy affects which instance is chosen for termination, but it does not preserve session state. Any terminated instance still loses its local sessions, and users bound to that instance will be disrupted. This does not make the application stateless or solve the session loss problem.
- ✗
Increase the instance size to reduce the likelihood of replacement.
Why it's wrong here
Larger instances do not address the fundamental issue of local session storage. Instances can still be replaced during scaling events, deployments, or failures, and any replacement will lose the session data. This does not make the application stateless and does not prevent user disruption.
- ✓
Store session state in an Amazon ElastiCache for Redis cluster.
Why this is correct
Externalizing session state to ElastiCache for Redis removes the dependency on local instance storage, allowing any instance in the Auto Scaling group to handle any user's request. When an instance is replaced, the session data remains available in the Redis cluster. This makes the application stateless and supports seamless scaling and recovery.
- ✗
Enable sticky sessions on the Application Load Balancer.
Why it's wrong here
Sticky sessions bind a user to a specific instance, which preserves session state only as long as that instance is healthy. If the instance is replaced or fails, the session is lost. This approach does not make the application stateless and can lead to uneven load distribution, so it does not meet the requirement.
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Amazon Web Services exam blueprint
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.