The correct approach is to create a new target group with the green instances and modify the ALB listener rule to forward traffic to that new target group. This works because the Application Load Balancer’s listener rules can instantly shift traffic between target groups at the rule priority level, enabling zero-downtime deployment without altering DNS records or provisioning a second ALB. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this scenario tests your understanding of how to decouple deployment from infrastructure changes—a common trap is assuming you need a new ALB or Route53 weight changes, which add latency and complexity. Instead, remember that ALB listener rules are the fastest, most atomic way to switch traffic, and the old target group remains intact for immediate rollback. Memory tip: think “Rule, not Route”—the listener rule is the switch, not the DNS.
SAP-C02 Design for New Solutions Practice Question
This SAP-C02 practice question tests your understanding of design for new 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 web application on Amazon EC2 instances behind an Application Load Balancer (ALB). They want to implement a blue/green deployment strategy with minimal impact on users. Which approach should they use?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a new target group with the green instances. Modify the ALB listener rule to forward traffic to the new target group.
Option A is correct because blue/green deployment with an ALB is achieved by creating a new target group for the green instances and modifying the ALB listener rule to forward traffic to the new target group. This allows instant traffic shifting with zero downtime, as the ALB can route traffic between target groups without changing the DNS or creating a new ALB. The blue (old) target group remains available for instant rollback if needed.
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.
✓
Create a new target group with the green instances. Modify the ALB listener rule to forward traffic to the new target group.
Why this is correct
This is the standard blue/green deployment with ALB.
Related concept
Read the scenario before looking for a memorised answer.
✗
Stop all instances, launch new instances with the new version, and update the target group.
Why it's wrong here
This causes downtime.
✗
Update the existing target group's instances to the new version, one at a time.
Why it's wrong here
This is a rolling update, not blue/green.
✗
Create a new ALB and update DNS to point to the new ALB.
Why it's wrong here
This is a manual cutover, not seamless.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is confusing blue/green deployment with rolling updates or assuming that a new ALB and DNS change are required, when in fact ALB listener rule modifications provide immediate traffic switching without DNS propagation delays.
Detailed technical explanation
How to think about this question
The ALB listener rule supports weighted target groups, allowing gradual traffic shifting (e.g., 10% to green, 90% to blue) for canary testing before full cutover. The blue target group remains registered with the ALB but receives zero traffic after the rule update, enabling instant rollback by reverting the listener rule. This approach avoids DNS TTL (Time to Live) propagation issues, which can take minutes to hours depending on client caching.
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.
Design for New Solutions — This question tests Design for New Solutions — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Create a new target group with the green instances. Modify the ALB listener rule to forward traffic to the new target group. — Option A is correct because blue/green deployment with an ALB is achieved by creating a new target group for the green instances and modifying the ALB listener rule to forward traffic to the new target group. This allows instant traffic shifting with zero downtime, as the ALB can route traffic between target groups without changing the DNS or creating a new ALB. The blue (old) target group remains available for instant rollback if needed.
What should I do if I get this SAP-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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Question Discussion
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