Discuss Amazon SOA-C03 Exam Topic 4 Question 12

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A company uses an Amazon Simple Queue Service (Amazon SQS) queue and Amazon EC2 instances in an Auto Scaling group with target tracking for a web application. The company collects the ASGAverageNetworkIn metric but notices that instances do not scale fast enough during peak traffic. There are a large number of SQS messages accumulating in the queue.

A CloudOps engineer must reduce the number of SQS messages during peak periods.

Which solution will meet this requirement?

ADefine and use a new custom Amazon CloudWatch metric based on the SQS ApproximateNumberOfMessagesDelayed metric in the target tracking policy.

BDefine and use Amazon CloudWatch metric math to calculate the SQS queue backlog for each instance in the target tracking policy.

CDefine and use step scaling by specifying a ChangeInCapacity value for the EC2 instances.

DDefine and use simple scaling by specifying a ChangeInCapacity value for the EC2 instances.

Suggested Answer: B

According to the AWS Cloud Operations and Auto Scaling documentation, scaling applications that consume Amazon SQS messages should be driven by queue backlog per instance, not by general system metrics such as network traffic or CPU.

The correct approach is to calculate a custom metric using CloudWatch metric math that divides the SQS metric ApproximateNumberOfMessagesVisible by the number of active EC2 instances in the Auto Scaling group. This ''backlog per instance'' value represents the average number of messages waiting to be processed by each instance.

Then, the CloudOps engineer can create a target tracking policy that automatically scales out or in based on maintaining a desired backlog threshold. This approach ensures dynamic, workload-driven scaling behavior that reacts in near real time to message volume.

Step and simple scaling (Options C and D) require manual thresholds and do not automatically balance the load per instance.

Thus, Option B---using CloudWatch metric math to define queue backlog per instance for target tracking---is the most effective and AWS-recommended CloudOps practice.

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23 comments · newest first

Laura Evans 15 days ago

My answer is A since tricky part is backlog per instance, which needs metric math dividing visible messages by active instances, not the delayed metric.

Monica Nelson 1 day ago

↳ replying to Laura Evans

Doesn't the backlog per instance requirement point to B instead of A since A relies on the delayed metric?

Amira Sheikh 7 days ago

↳ replying to Laura Evans

Makes sense, I landed on B as well.

Tawanna 2 months ago

I agree with B. Calculating backlog gives better insights.

Halina 2 months ago

Option D seems too basic. We need something more dynamic.

Nell 2 months ago

I'm leaning towards A as well. Delayed messages are a big issue.

Miesha 2 months ago

Option C could work too. Step scaling might react faster.

Antione 3 months ago

I prefer option B. Metric math sounds more precise for backlog.

Curtis 3 months ago

I think option A is the best. Custom metrics can really help track delays.

Tammara 3 months ago

D) is too basic for this situation, we need something smarter!

Jacki 3 months ago

Wait, how does A) even help with scaling?

Lura 3 months ago

C) could work, but it might not be fast enough.

Hubert 3 months ago

I disagree, B) might give better insights into the backlog.

Izetta 4 months ago

A) seems like the best option for tracking delays.

Kanisha 4 months ago

D) seems outdated, we need to be more dynamic!

Mabel 4 months ago

Wait, why not just increase the instance size instead?

Xuan 4 months ago

C) is too basic for peak traffic, needs more finesse.

Joanne 6 months ago

I think B) could give more insight into the backlog.

Audra 6 months ago

A) sounds like a solid choice for tracking delays.

Valentin 6 months ago

I’m leaning towards option A, but I’m not entirely confident about how the delayed messages metric works in this context.

Julio 7 months ago

I feel like step scaling could be a good choice, but I can't recall the exact differences between step and simple scaling.

Portia 7 months ago

I think option B sounds familiar; we practiced calculating backlog metrics in a similar question. That might help with scaling.

Ona 7 months ago

I remember we discussed using custom CloudWatch metrics, but I'm not sure if that would be the best approach here.

Amazon SOA-C03 Exam - Topic 4 Question 12 Discussion