Question 232 of 247
SOA-C02 Deployment, Provisioning, and Automation Practice Question
A company has a legacy application that runs on a single Amazon EC2 instance. The SysOps administrator is tasked with migrating the application to an Auto Scaling group behind an Application Load Balancer to improve availability. The application stores session state locally on the instance. What should the administrator do to ensure a seamless migration with minimal changes to the application code?
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 Amazon ElastiCache for Redis to store session data externally.
Using Amazon ElastiCache for Redis to store session data externally allows the application to be stateless, enabling seamless scaling across multiple EC2 instances in an Auto Scaling group. This approach requires minimal code changes (typically just configuring the application to use a Redis endpoint instead of local storage) and ensures session data is not lost if an instance fails. Option A (sticky sessions) is a workaround but does not eliminate the dependency on local storage; sessions are still lost if an instance fails. Option B (disabling local session storage) does not solve the problem because the application still needs persistent session storage. Option D (using RDS) is possible but is not the best choice for session data because relational databases are typically slower for session caching and require more significant code and schema changes compared to Redis, which is an in-memory data store optimized for session management.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
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Configure the Application Load Balancer with sticky sessions (session affinity).
Why it's wrong here
Sticky sessions (session affinity) keep a user's requests routed to the same instance, but if that instance fails, the session data is lost because it is still stored locally. This does not eliminate the dependency on local storage.
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Disable the feature that stores session state locally.
Why it's wrong here
Simply disabling the application's local session-state feature does not provide an alternative persistence mechanism. User sessions still need to be stored somewhere that is shared and durable across instances; without such a store, session data will be lost on every request or instance failure. The correct approach is to replace local storage with an external, centralized store such as ElastiCache for Redis, which maintains session continuity while keeping the application stateless.
- ✓
Use Amazon ElastiCache for Redis to store session data externally.
Why this is correct
Amazon ElastiCache for Redis provides a fast, in-memory data store that can hold session data externally. This makes the application stateless, allowing any instance in the Auto Scaling group to handle requests without losing session data. Requires minimal code changes.
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Modify the application to store session data in an Amazon RDS database.
Why it's wrong here
Storing session data in Amazon RDS introduces a relational database dependency that requires modifying the application’s session-handling code to use SQL queries, contradicting the requirement for minimal code changes. This option is tempting because RDS is a common choice for persistent, shared state in distributed architectures and would be correct if the application already used a database for session storage or if the team accepted code rewrites.
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Last reviewed: Jun 20, 2026
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