PAS-C01 Technology Practice Question
A company runs a stateful web application on EC2 instances in an Auto Scaling group with a dynamic scaling policy based on CPU utilization. The application maintains session state in memory on each instance. Users report that they are frequently logged out and lose their session data during scaling events. What should the company do to resolve this issue?
⚠ Common exam trap
Test-takers frequently confuse sticky sessions (session affinity) with true session persistence, not realizing that sticky sessions only route traffic to the same instance but do not protect against instance termination during scaling events.
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
✓
Modify the application to store session state in an Amazon ElastiCache cluster
Storing session state externally in ElastiCache decouples session data from individual EC2 instances. This ensures that when instances are terminated or added during scaling events, users retain their session state regardless of which instance serves their request. ElastiCache provides a low-latency, in-memory cache that is ideal for session persistence in stateful web applications.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Change the scaling policy to a simple scaling policy instead of dynamic scaling
Why it's wrong here
Simple scaling does not prevent session loss; the core issue is that session state is stored in memory on the instance.
- ✗
Enable sticky sessions (session affinity) on the Application Load Balancer
Why it's wrong here
Stickiness routes users to the same instance, but if that instance is terminated due to scaling in, the session is still lost.
- ✓
Modify the application to store session state in an Amazon ElastiCache cluster
Why this is correct
ElastiCache provides a centralized session store that persists across instance terminations, ensuring session continuity during scaling events.
- ✗
Increase the cooldown period for the Auto Scaling group
Why it's wrong here
Cooldown period only affects when new scaling activities can start; it does not preserve session data.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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