PAS-C01 Operations and Maintenance Practice Question
A company runs a web application on Amazon ECS with Fargate launch type. The application's memory utilization spikes periodically, causing tasks to be killed. The operations team wants to automatically scale the service based on memory usage. Which TWO steps are necessary to implement this?
⚠ Common exam trap
A common mix-up: candidates think a CloudWatch alarm is required to trigger scaling, but target tracking scaling policies use the metric directly without an alarm. Also, they may confuse Fargate with EC2 launch type and try to use an Auto Scaling group.
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
✓
Create an Application Auto Scaling target tracking scaling policy based on memory utilization.
Options B and E are necessary. B: Application Auto Scaling with a target tracking scaling policy automatically adjusts the desired task count to maintain a target memory utilization, preventing OOM kills. E: The ECS service must publish custom CloudWatch metrics for memory utilization because Fargate does not publish memory metrics by default; enabling this makes the metric available for the scaling policy. Option D is not necessary because target tracking scaling policies use the metric directly without requiring a separate CloudWatch alarm.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Attach an EC2 Auto Scaling group to the ECS service to handle capacity.
Why it's wrong here
Attaching an EC2 Auto Scaling group is not needed for Fargate launch type; it is used for EC2 launch type.
- ✓
Create an Application Auto Scaling target tracking scaling policy based on memory utilization.
Why this is correct
Correct. Target tracking scaling policy automatically adjusts capacity to maintain the target metric value.
- ✗
Configure step scaling policies to add multiple tasks at once.
Why it's wrong here
Step scaling policies are not the primary mechanism for automatically maintaining a target memory utilisation. While they allow adding multiple tasks, they respond to alarm breaches with predefined steps, rather than continuously adjusting to keep a metric at a desired level. This option is tempting as it scales services, and is appropriate for aggressive, step-wise scaling actions when an alarm crosses a threshold, for instance, adding more tasks the higher the alarm value.
- ✗
Create a CloudWatch alarm that triggers the scaling policy when memory exceeds a threshold.
Why it's wrong here
Incorrect. Creating a CloudWatch alarm is not necessary because the target tracking scaling policy uses the metric directly.
- ✓
Enable the ECS service to publish custom CloudWatch metrics for memory utilization.
Why this is correct
Correct. Custom CloudWatch metrics for memory must be enabled because Fargate does not publish memory metrics by default.
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