SOA-C03 practice question: EC2 Auto Scaling (3 of 3)

Reliability and Business Continuity A free question from our original SOA-C03 practice exam. Try it, then open the answer to see why each option is right or wrong.

A regional bank's branch application runs in an EC2 Auto Scaling group. Every weekday at 8:00, when branches open, CPU jumps from 15 percent to 80 percent within minutes, and the group takes 10 minutes to catch up. During the rest of the day, load rises and falls without a pattern. The team wants capacity ready before the morning surge and steady CPU near 50 percent the rest of the day. Which TWO scaling policies should a CloudOps engineer configure? (Choose two.)

Choose two answers.

A. A target tracking policy that keeps the group's average CPU utilization at 50 percent.
B. A step scaling policy on memory utilization from the AWS/EC2 namespace that adds instances in larger steps.
C. A predictive scaling policy that learns the weekday pattern and launches capacity ahead of the 8:00 surge.
D. An instance refresh scheduled for 7:45 every weekday so that new instances are running when the branches open.
E. A simple scaling policy with a 30-minute cooldown that adds one instance each time CPU passes 70 percent.

Show the answer and explanation

Answers: A, C

A. Right: Correct. Target tracking adds and removes instances to hold a metric near its target value. It handles the unpatterned load during the rest of the day. Learn more: Target tracking scaling policies for Amazon EC2 Auto Scaling (opens in a new tab)
B. Wrong: EC2 does not publish memory utilization in the AWS/EC2 namespace, so this metric does not exist without the CloudWatch agent. The problem is also CPU, not memory. Learn more: Step and simple scaling policies for Amazon EC2 Auto Scaling (opens in a new tab)
C. Right: Correct. Predictive scaling forecasts load from daily and weekly history and schedules capacity before the expected rise. The repeating weekday opening is exactly the pattern it learns. Learn more: Predictive scaling for Amazon EC2 Auto Scaling (opens in a new tab)
D. Wrong: Instance refresh replaces existing instances to roll out a new configuration. It does not add capacity and would briefly reduce healthy capacity before the surge. Learn more: Use an instance refresh to update instances in an Auto Scaling group (opens in a new tab)
E. Wrong: A simple policy adds one instance and then waits for the cooldown before acting again. A 30-minute cooldown makes the response to the surge even slower. Learn more: Step and simple scaling policies for Amazon EC2 Auto Scaling (opens in a new tab)

Explanation

Auto Scaling policies can work together. Predictive scaling handles the known weekday spike by launching capacity before it arrives, and target tracking handles everything else by holding CPU near the target. When policies overlap, the group uses the one that gives the larger capacity.

SOA-C03 practice question: EC2 Auto Scaling (3 of 3)

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