- A
Increase the deregistration delay on the target group.
Why wrong: Increasing the deregistration delay is not necessarily required; the necessary step is to enable connection draining (i.e., set a non-zero deregistration delay). While increasing the delay could help, it is not the core requirement. Enabling the feature is what allows in-flight requests to complete.
- B
Reduce the stickiness duration to zero.
Why wrong: Reducing the stickiness duration to zero does not help drain existing connections. It only stops new sessions from being sticky, but existing sticky sessions will continue to route to the same instance until the cookie expires. The instance can still be terminated without waiting for those requests.
- C
Configure health checks to mark instances unhealthy.
Why wrong: Configuring health checks to mark instances unhealthy stops new traffic but does not wait for in-flight requests to finish. Without connection draining, the instance can be deregistered immediately and terminated while requests are still being processed.
- D
Enable connection draining on the target group.
Enabling connection draining (deregistration delay) on the target group is the necessary step. It configures the ALB to wait for in-flight requests to complete before fully deregistering the instance, allowing graceful termination even with sticky sessions.
ALB Connection Draining for Sticky Sessions
This DOP-C02 practice question tests your understanding of resilient cloud solutions. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 application on EC2 that requires sticky sessions. They use an ALB with duration-based stickiness. During a deployment, they want to drain existing connections gracefully before terminating instances. Which step is necessary?
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 connection draining on the target group.
Option D is correct because ALB target groups use a 'deregistration delay' (formerly called connection draining) to allow in-flight requests to complete before an instance is terminated. This setting is configured on the target group, not the load balancer, and it works with sticky sessions by waiting for the delay period (default 300 seconds) for existing connections to finish, even if the stickiness cookie would otherwise route new requests to the same instance. During a deployment, increasing this delay or ensuring it is set appropriately is the necessary step to gracefully drain connections.
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.
- ✗
Increase the deregistration delay on the target group.
Why it's wrong here
Increasing the deregistration delay is not necessarily required; the necessary step is to enable connection draining (i.e., set a non-zero deregistration delay). While increasing the delay could help, it is not the core requirement. Enabling the feature is what allows in-flight requests to complete.
- ✗
Reduce the stickiness duration to zero.
Why it's wrong here
Reducing the stickiness duration to zero does not help drain existing connections. It only stops new sessions from being sticky, but existing sticky sessions will continue to route to the same instance until the cookie expires. The instance can still be terminated without waiting for those requests.
- ✗
Configure health checks to mark instances unhealthy.
Why it's wrong here
Configuring health checks to mark instances unhealthy stops new traffic but does not wait for in-flight requests to finish. Without connection draining, the instance can be deregistered immediately and terminated while requests are still being processed.
- ✓
Enable connection draining on the target group.
Why this is correct
Enabling connection draining (deregistration delay) on the target group is the necessary step. It configures the ALB to wait for in-flight requests to complete before fully deregistering the instance, allowing graceful termination even with sticky sessions.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse 'connection draining' (which is the deregistration delay on ALB target groups) with 'sticky session duration' or 'health check settings,' thinking that reducing stickiness or marking instances unhealthy alone will gracefully terminate connections, when in fact the deregistration delay is the specific mechanism that waits for in-flight requests to complete.
Detailed technical explanation
How to think about this question
Under the hood, the deregistration delay is a target group attribute that controls how long the ALB waits for in-flight requests to complete after an instance is deregistered or becomes unhealthy. During this period, the ALB continues to route existing connections to the instance while new connections are sent to healthy instances. In a deployment scenario with sticky sessions, the deregistration delay ensures that users with active sessions do not lose their state mid-request, which is critical for stateful applications. A real-world scenario is a blue/green deployment where you must wait for all sessions to drain before terminating the old instances.
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
A cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
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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FAQ
Questions learners often ask
What does this DOP-C02 question test?
Resilient Cloud Solutions — This question tests Resilient Cloud Solutions — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Enable connection draining on the target group. — Option D is correct because ALB target groups use a 'deregistration delay' (formerly called connection draining) to allow in-flight requests to complete before an instance is terminated. This setting is configured on the target group, not the load balancer, and it works with sticky sessions by waiting for the delay period (default 300 seconds) for existing connections to finish, even if the stickiness cookie would otherwise route new requests to the same instance. During a deployment, increasing this delay or ensuring it is set appropriately is the necessary step to gracefully drain connections.
What should I do if I get this DOP-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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