The answer is to enable connection draining on the ALB target group. This feature, also known as deregistration delay, allows the load balancer to finish serving existing WebSocket connections and in-flight requests before terminating the EC2 instance during a scale-in event, preventing abrupt user disconnections. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this scenario tests your understanding of how to maintain WebSocket connections during scale-in with connection draining, often appearing as a trap where candidates confuse sticky sessions or lifecycle hooks with connection management. A common mistake is assuming sticky sessions alone preserve connections, but they only route traffic, not wait for completion. Remember the mnemonic: “Drain before you gain”—connection draining lets connections finish before the instance is removed, keeping your WebSocket users seamlessly connected.
SAP-C02 Continuous Improvement for Existing Solutions Practice Question
This SAP-C02 practice question tests your understanding of continuous improvement for existing solutions. 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 behind an Application Load Balancer (ALB). The application uses WebSockets for real-time communication. During scale-in events, users experience disconnections. How can the company maintain WebSocket connections during scaling?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Enable connection draining on the ALB target group.
Option D is correct because enabling connection draining on the ALB target group allows in-flight requests and WebSocket connections to complete before the instance is deregistered. Option A is wrong because sticky sessions do not prevent disconnections during scale-in. Option B is wrong because ASG lifecycle hooks do not affect ALB connections. Option C is wrong because a Network Load Balancer is for TCP/UDP, not HTTP/WebSocket at the application layer.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 ALB with a Network Load Balancer (NLB).
Why it's wrong here
NLB supports WebSockets but still requires connection draining.
✗
Use sticky sessions (session affinity) on the ALB.
Why it's wrong here
Sticky sessions route users to the same instance but do not prevent disconnections when the instance is terminated.
✓
Enable connection draining on the ALB target group.
Why this is correct
Connection draining allows existing connections to complete before the instance is deregistered.
Related concept
Static NAT maps one inside address to one outside address.
✗
Use an Auto Scaling lifecycle hook to delay instance termination.
Why it's wrong here
Lifecycle hooks delay termination but do not drain connections from ALB.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related SAP-C02 NAT questions on configuration and troubleshooting.
Continuous Improvement for Existing Solutions — This question tests Continuous Improvement for Existing Solutions — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Enable connection draining on the ALB target group. — Option D is correct because enabling connection draining on the ALB target group allows in-flight requests and WebSocket connections to complete before the instance is deregistered. Option A is wrong because sticky sessions do not prevent disconnections during scale-in. Option B is wrong because ASG lifecycle hooks do not affect ALB connections. Option C is wrong because a Network Load Balancer is for TCP/UDP, not HTTP/WebSocket at the application layer.
What should I do if I get this SAP-C02 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related SAP-C02 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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