- A
Replace the Application Load Balancer with a Network Load Balancer. Enable proxy protocol v2 to pass client IP addresses.
Why wrong: A Network Load Balancer does not natively support sticky sessions based on cookies. This would break session persistence.
- B
Enable sticky sessions (session affinity) on the ALB. Configure a lifecycle hook on the Auto Scaling group with a wait time equal to the ALB's connection draining timeout.
Sticky sessions route requests to the same instance; lifecycle hooks delay termination until draining completes, preserving sessions.
- C
Increase the Auto Scaling group's cooldown period to 600 seconds. Configure the ALB to have a deregistration delay of 600 seconds.
Why wrong: This delays the termination but still does not ensure that subsequent requests are sent to the same instance. Sticky sessions are needed.
- D
Configure the Auto Scaling group to scale based on memory utilization instead of CPU. Set the cooldown period to 300 seconds.
Why wrong: Changing the scaling metric does not solve session stickiness. Cooldown delays scaling but does not prevent session loss during scale-in.
Session Persistence with Sticky Sessions and Lifecycle Hook
This SOA-C02 practice question tests your understanding of reliability and business continuity. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company runs a stateful web application on EC2 instances in an Auto Scaling group across two Availability Zones. The application uses an Application Load Balancer for traffic distribution. Users report that their sessions are frequently lost during scale-in events. The SysOps administrator needs to minimize session loss without introducing significant latency. What should the administrator do?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"minimum / minimize"Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
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 (session affinity) on the ALB. Configure a lifecycle hook on the Auto Scaling group with a wait time equal to the ALB's connection draining timeout.
Option B is correct because enabling sticky sessions (session affinity) on the ALB ensures that a client's requests are consistently routed to the same EC2 instance, preventing session loss during scale-in. Configuring a lifecycle hook on the Auto Scaling group with a wait time equal to the ALB's connection draining timeout (deregistration delay) allows in-flight requests to complete before the instance is terminated, minimizing session disruption without adding significant latency.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Replace the Application Load Balancer with a Network Load Balancer. Enable proxy protocol v2 to pass client IP addresses.
Why it's wrong here
A Network Load Balancer does not natively support sticky sessions based on cookies. This would break session persistence.
- ✓
Enable sticky sessions (session affinity) on the ALB. Configure a lifecycle hook on the Auto Scaling group with a wait time equal to the ALB's connection draining timeout.
Why this is correct
Sticky sessions route requests to the same instance; lifecycle hooks delay termination until draining completes, preserving sessions.
Clue confirmation
The clue word "minimum / minimize" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Increase the Auto Scaling group's cooldown period to 600 seconds. Configure the ALB to have a deregistration delay of 600 seconds.
Why it's wrong here
This delays the termination but still does not ensure that subsequent requests are sent to the same instance. Sticky sessions are needed.
- ✗
Configure the Auto Scaling group to scale based on memory utilization instead of CPU. Set the cooldown period to 300 seconds.
Why it's wrong here
Changing the scaling metric does not solve session stickiness. Cooldown delays scaling but does not prevent session loss during scale-in.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume increasing timeouts (cooldown or deregistration delay) alone is sufficient, but without a lifecycle hook to coordinate the Auto Scaling group with the ALB's draining process, instances can be terminated prematurely, causing session loss.
Detailed technical explanation
How to think about this question
Sticky sessions on an ALB use a cookie (AWSALB or custom) to bind a client to a specific target instance; the lifecycle hook pauses the Auto Scaling group's instance termination process, allowing the ALB's connection draining (deregistration delay) to complete active requests. Under the hood, the lifecycle hook sends a heartbeat to keep the instance in a 'waiting' state until the ALB finishes draining, then the hook completes to allow termination. In real-world scenarios, this combination is critical for stateful applications like e-commerce carts or gaming sessions where losing a session mid-transaction causes user frustration.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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Reliability and Business Continuity — study guide chapter
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FAQ
Questions learners often ask
What does this SOA-C02 question test?
Reliability and Business Continuity — This question tests Reliability and Business Continuity — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Enable sticky sessions (session affinity) on the ALB. Configure a lifecycle hook on the Auto Scaling group with a wait time equal to the ALB's connection draining timeout. — Option B is correct because enabling sticky sessions (session affinity) on the ALB ensures that a client's requests are consistently routed to the same EC2 instance, preventing session loss during scale-in. Configuring a lifecycle hook on the Auto Scaling group with a wait time equal to the ALB's connection draining timeout (deregistration delay) allows in-flight requests to complete before the instance is terminated, minimizing session disruption without adding significant latency.
What should I do if I get this SOA-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "minimum / minimize". Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
2 more ways this is tested on SOA-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 company runs a stateful web application on EC2 instances in an Auto Scaling group behind an Application Load Balancer. Users report that their sessions are frequently lost during scaling events. What is the MOST effective solution to maintain session persistence?
hard- A.Increase the cooldown period for the Auto Scaling group.
- ✓ B.Modify the application to store session data in an external data store such as ElastiCache or DynamoDB.
- C.Enable sticky sessions (session affinity) on the Application Load Balancer.
- D.Use larger EC2 instance types to reduce the frequency of scaling.
Why B: Externalizing session state to a durable, shared data store like ElastiCache or DynamoDB decouples session data from individual EC2 instances. This ensures that sessions survive scaling events, including instance termination during scale-in, because any instance can retrieve the session from the external store. Sticky sessions (option C) only route traffic to the same instance, but they do not preserve session data if that instance is terminated. Options A and D do not address session persistence at all.
Variation 2. A company runs a stateful web application on EC2 instances in an Auto Scaling group. The application uses a sticky session (session affinity) feature of the Application Load Balancer. During a scale-in event, some users lose their session data. What should the SysOps administrator do to prevent session data loss?
hard- A.Disable sticky sessions and use a round-robin routing algorithm.
- ✓ B.Store session state in an external data store such as Amazon ElastiCache.
- C.Use a lifecycle hook to back up session data before termination.
- D.Increase the Auto Scaling group's cooldown period to delay termination.
Why B: Sticky sessions (session affinity) tie a user's session to a specific EC2 instance. When a scale-in event terminates that instance, the session data stored locally on the instance is lost. Storing session state in an external data store like Amazon ElastiCache decouples session data from individual instances, allowing any healthy instance to serve the user's request without data loss, even after a scale-in event.
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Last reviewed: Jul 4, 2026
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