SAP-C02 Design for New Solutions Practice Question
A company is designing a new application that will run on Amazon EC2 instances in an Auto Scaling group behind an Application Load Balancer. The application must maintain session state. The company expects steady traffic with occasional spikes. Which solution is MOST scalable and cost-effective?
⚠ Common exam trap
Many exam-takers choose sticky sessions (Option A) because it seems simple and directly supported by ALB, but they overlook the fundamental scalability and resilience issues it introduces in an Auto Scaling environment.
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.
Amazon ElastiCache for Redis provides a highly scalable, low-latency, and durable external session store that decouples session state from EC2 instances. This allows the Auto Scaling group to add or remove instances freely without losing session data, and Redis supports replication and persistence for reliability. Compared to DynamoDB, Redis offers lower latency for session access, and compared to Memcached, it provides data structures and persistence that are beneficial 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 sticky sessions (session affinity) on the ALB with a session cookie.
Why it's wrong here
Sticky sessions reduce scalability as instances cannot be terminated easily.
- ✗
Use Amazon ElastiCache for Memcached to store session data.
Why it's wrong here
ElastiCache for Memcached lacks built-in replication and failover, so a node failure would erase all session data, breaking state continuity during traffic spikes when Auto Scaling launches new instances. It is tempting because Memcached offers low-latency, distributed caching for transient data, and would be correct for a stateless application where session loss is acceptable and only read-heavy caching is needed.
- ✗
Store session data in Amazon DynamoDB tables.
Why it's wrong here
DynamoDB is more expensive and higher latency for session storage.
- ✓
Use Amazon ElastiCache for Redis to store session data externally.
Why this is correct
Redis provides a scalable, highly available session store.
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Same concept, more angles
3 more ways this is tested on SAP-C02
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 solutions architect is designing a web application that will run on Amazon EC2 instances behind an Application Load Balancer (ALB). The application requires that users' session data be stored and made available across all instances. Which solution is MOST cost-effective and scalable?
easy- ✓ A.Use Amazon ElastiCache for Redis to store session data
- B.Store session data on an Amazon EBS volume attached to each instance
- C.Store session data in an Amazon RDS database
- D.Enable sticky sessions (session affinity) on the ALB
Why A: Amazon ElastiCache for Redis provides a fully managed, in-memory data store that is ideal for storing session state externally from the EC2 instances. This decouples session data from the compute layer, allowing any instance to retrieve the same session data regardless of which instance originally handled the request. Redis offers sub-millisecond latency, built-in replication, and automatic failover, making it both highly scalable and cost-effective for session management at scale.
Variation 2. A company is designing a new application that will run on Amazon EC2 instances in an Auto Scaling group behind an Application Load Balancer. The application requires that users' session data be stored durably and with low latency. The session data is accessed frequently but is rarely updated. Which solution is MOST cost-effective?
medium- ✓ A.Use ElastiCache for Redis with replication.
- B.Store session data in Amazon S3 with reduced redundancy.
- C.Use DynamoDB with on-demand capacity.
- D.Use ElastiCache for Memcached with multiple nodes.
Why A: ElastiCache for Redis with replication is the most cost-effective solution because it provides durable, low-latency session storage with built-in replication for high availability. Redis supports persistence (e.g., snapshots or AOF logs) to ensure session data survives node failures, and its in-memory nature delivers sub-millisecond latency for frequent reads with rare updates, avoiding the higher costs of DynamoDB on-demand or the lack of durability in Memcached.
Variation 3. A company is designing a new application that will run on Amazon EC2 instances behind an Application Load Balancer. The application needs to store session state. Which AWS service provides a fully managed, highly scalable solution for session state management?
easy- A.Amazon DynamoDB
- ✓ B.Amazon ElastiCache for Redis
- C.Amazon S3
- D.Amazon RDS for MySQL
Why B: Amazon ElastiCache for Redis is the correct choice because it provides a fully managed, in-memory data store that is ideal for session state management. Redis offers sub-millisecond latency, built-in replication, and automatic failover, making it highly scalable and durable for session data. The Application Load Balancer can be configured with stickiness (session affinity) to route requests to the same EC2 instance, but using ElastiCache for Redis decouples session state from the compute layer, enabling stateless application tiers and seamless scaling.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SAP-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 SAP-C02 exam.