The answer is a blue/green deployment strategy with weighted target groups. This approach is correct because it enables you to gradually shift traffic from the monolithic EC2 application behind the Application Load Balancer to the new microservices running on ECS Fargate, allowing you to monitor for errors and instantly roll back by adjusting the weight distribution. For the AWS Certified Developer Associate DVA-C02 exam, this question tests your understanding of how to achieve minimal downtime migration by leveraging ALB features like target group weighting and health checks, which are essential for a seamless transition without disrupting active connections. A common trap is assuming a simple cutover or rolling update is sufficient, but those risk downtime or partial failures during the shift. Memory tip: think "blue/green with weighted ALB" as the safe, reversible bridge from monolith to microservices.
DVA-C02 Troubleshooting and Optimization Practice Question
This DVA-C02 practice question tests your understanding of troubleshooting and optimization. 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 monolithic application on EC2 Behind an Application Load Balancer. They want to migrate to a microservices architecture using ECS Fargate. What is the most important optimization to ensure minimal downtime during the migration?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use a blue/green deployment strategy with weighted target groups.
Option A is correct because a blue/green deployment strategy with weighted target groups allows you to gradually shift traffic from the existing monolithic EC2 application (blue) to the new microservices on ECS Fargate (green) while monitoring for errors. This minimizes downtime by enabling instant rollback if issues arise, and it leverages Application Load Balancer (ALB) features like stickiness and health checks to ensure a seamless transition without disrupting active 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.
✓
Use a blue/green deployment strategy with weighted target groups.
Why this is correct
Blue/green allows controlled traffic shift.
Related concept
Read the scenario before looking for a memorised answer.
✗
Increase the EC2 instance size to handle the microservices load.
Why it's wrong here
Instance size is irrelevant when moving to Fargate.
✗
Deploy all microservices in a single ECS service for simplicity.
Why it's wrong here
Single service contradicts microservices and increases risk.
✗
Scale horizontally by adding more EC2 instances.
Why it's wrong here
Horizontal scaling does not address migration downtime.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse scaling strategies (horizontal/vertical) with deployment strategies, assuming that adding more capacity or consolidating services will inherently reduce downtime, when in fact only a controlled traffic-shifting method like blue/green with weighted routing ensures minimal disruption during a live migration.
Detailed technical explanation
How to think about this question
Under the hood, ALB weighted target groups use the `weight` parameter in the `forward` action of a listener rule to distribute traffic as a percentage (e.g., 90% blue, 10% green). During migration, you can incrementally adjust weights (e.g., 50/50, then 10/90) while monitoring error rates and latency; if the green deployment fails, you can instantly set its weight to 0 for a zero-downtime rollback. This approach also works with ECS Fargate because the green target group points to an ECS service with a network load balancer (NLB) or ALB integration, and the blue group remains the original EC2 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
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.
Troubleshooting and Optimization — This question tests Troubleshooting and Optimization — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use a blue/green deployment strategy with weighted target groups. — Option A is correct because a blue/green deployment strategy with weighted target groups allows you to gradually shift traffic from the existing monolithic EC2 application (blue) to the new microservices on ECS Fargate (green) while monitoring for errors. This minimizes downtime by enabling instant rollback if issues arise, and it leverages Application Load Balancer (ALB) features like stickiness and health checks to ensure a seamless transition without disrupting active connections.
What should I do if I get this DVA-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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