AWS Certified Solutions Architect Associate · Free Practice Question Medium
Question 17
A company runs an internal browser-based application. The application runs on Amazon EC2 instances behind an Application Load Balancer. The instances run in an Amazon EC2 Auto Scaling group across multiple Availability Zones. The Auto Scaling group scales up to 20 instances during work hours, but scales down to 2 instances overnight. Staff are complaining that the application is very slow when the day begins, although it runs well by midmorning
How should the scaling be changed to address the staff complaints and keep costs to a minimum?
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A
Implement a scheduled action that sets the desired capacity to 20 shortly before the office opens
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B
Implement a step scaling action triggered at a lower CPU threshold, and decrease the cooldown period
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C
Implement a scheduled action that sets the minimum and maximum capacity to 20 shortly before the office opens
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D
Implement a target tracking action triggered at a lower CPU threshold, and decrease the cooldown period
Reveal correct answer
Correct answer: D
Explanation
Though this sounds like a good use case for scheduled actions, both answers using scheduled actions will have 20 instances running regardless of actual demand. A better option to be more cost effective is to use a target tracking action that triggers at a lower CPU threshold.
With this solution the scaling will occur before the CPU utilization gets to a point where performance is affected. This will result in resolving the performance issues whilst minimizing costs. Using a reduced cooldown period will also more quickly terminate unneeded instances, further reducing costs.
CORRECT: "Implement a target tracking action triggered at a lower CPU threshold, and decrease the cooldown period" is the correct answer.
INCORRECT: "Implement a scheduled action that sets the desired capacity to 20 shortly before the office opens" is incorrect as this is not the most cost-effective option. Note you can choose min, max, or desired for a scheduled action.
INCORRECT: "Implement a scheduled action that sets the minimum and maximum capacity to 20 shortly before the office opens" is incorrect as this is not the most cost-effective option. Note you can choose min, max, or desired for a scheduled action.
INCORRECT: "Implement a step scaling action triggered at a lower CPU threshold, and decrease the cooldown period" is incorrect as AWS recommend you use target tracking in place of step scaling for most use cases.
References:
https://docs.aws.amazon.com/autoscaling/ec2/userguide/as-scaling-target-tracking.html
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Discussion
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