SAP-C02 Design for New Solutions Practice Question
A company is migrating a legacy monolithic application to AWS. The application stores session state locally on each server. The company wants to refactor the application to be stateless and deploy it across multiple Availability Zones for high availability. The application must handle sudden traffic spikes and maintain session persistence. Which solution should a solutions architect recommend?
⚠ Common exam trap
The trap here is thinking that sticky sessions solve the session state problem, but they actually prevent the application from becoming stateless and reduce availability.
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 with Multi-AZ enabled, and configure the application to use it.
ElastiCache for Redis with Multi-AZ is the best choice because it provides a highly available, low-latency, in-memory session store that externalizes session state, making the application stateless. It scales to handle traffic spikes and ensures session persistence across AZs with automatic failover. Other options either keep the application stateful, introduce latency, or are not 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.
- ✗
Use Application Load Balancer with sticky sessions (session affinity) and store session state on each EC2 instance's local disk.
Why it's wrong here
Sticky sessions with local storage keep the application stateful. If an instance fails, the session data is lost, and users are disrupted. Sticky sessions can also lead to uneven load distribution, especially during traffic spikes. This approach does not achieve true statelessness or high availability across AZs, as required.
- ✗
Store session state in an Amazon S3 bucket and have the application read and write session data for each request.
Why it's wrong here
S3 is object storage with higher latency than in-memory caches. Using S3 for session state on every request would introduce significant latency and is not suitable for high-traffic, low-latency session management. S3 is not designed for frequent small reads/writes, and it lacks the atomic operations needed for session updates. This would degrade performance and user experience.
- ✓
Store session state in an Amazon ElastiCache for Redis cluster with Multi-AZ enabled, and configure the application to use it.
Why this is correct
ElastiCache for Redis with Multi-AZ provides a highly available, in-memory session store that is external to the application servers. This makes the application stateless and allows it to scale horizontally across AZs. Redis supports persistence and automatic failover, ensuring session data survives node failures. It is ideal for handling sudden traffic spikes due to its low latency and high throughput.
- ✗
Use Amazon DynamoDB with a global secondary index to store session state, and configure the application to use it.
Why it's wrong here
DynamoDB can store session state and scale, but it has higher latency than an in-memory cache like Redis. For session data that must be accessed on every request, the millisecond latency of DynamoDB may be acceptable but not optimal for sudden spikes. It also requires more complex code to handle session expiration and consistency. ElastiCache for Redis is purpose-built for this use case.
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Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Amazon Web Services exam blueprint
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