SAP-C02 Design for New Solutions Practice Question
A company is designing a new web application that will run on Amazon EC2 instances behind an Application Load Balancer (ALB). The application must support sticky sessions. What should they do?
⚠ Common exam trap
Many exam-takers confuse stateless session management (e.g., ElastiCache) with ALB sticky sessions, or incorrectly assume that CloudFront or NLB can provide HTTP-level session affinity, when only ALB duration-based cookies directly satisfy the requirement for sticky sessions on the load balancer.
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
✓
Enable sticky sessions on the ALB using duration-based cookies.
Application Load Balancers natively support sticky sessions (session affinity) using duration-based cookies. The ALB generates a cookie (AWSALB) that binds a user's session to a specific target instance for the duration of the cookie's lifetime, ensuring consistent user experience without external dependencies.
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 an Amazon CloudFront distribution with session affinity.
Why it's wrong here
CloudFront terminates client connections at edge locations and forwards requests to the ALB; it cannot pin a user to a specific EC2 target, so ALB session stickiness is bypassed. It is tempting because CloudFront offers origin affinity, which is useful for caching or regional routing, not per-instance session state.
- ✗
Store session data in Amazon ElastiCache and use a cookie to reference it.
Why it's wrong here
Externalising sessions to ElastiCache with a cookie reference makes the application stateless, so no instance affinity is needed; the ALB still requires stickiness configuration to satisfy the stated requirement. It is tempting because centralised session stores are the standard pattern for horizontally scaled, fault-tolerant web tiers.
- ✓
Enable sticky sessions on the ALB using duration-based cookies.
Why this is correct
ALB duration-based cookies issue an AWSELB cookie that binds each client to the same target for the configured duration, satisfying the sticky-session requirement. This operates at the load balancer layer, requiring no application changes on the EC2 instances.
- ✗
Use a Network Load Balancer (NLB) with cross-zone load balancing.
Why it's wrong here
NLB operates at layer 4 and balances TCP/UDP flows; it lacks HTTP cookie processing, so it cannot generate the AWSALB stickiness cookie the ALB requires. Cross-zone load balancing only redistributes traffic across AZs. NLB is correct for ultra-low-latency TCP or static IP requirements, not HTTP session affinity.
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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.