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Difficulty: MediumAuto Scaling and Elasticity

A company runs a web application on Amazon EC2 instances managed by an Auto Scaling group. The group is configured with a target tracking scaling policy based on the `ASGAverageCPUUtilization` metric with a target value of 60%60\%. During sudden traffic spikes, the Auto Scaling group launches new instances to handle the load. However, the newly launched instances require approximately 55 minutes to download application packages, run bootstrapping scripts, and begin processing requests. During this startup period, the Auto Scaling group continues to launch additional instances, resulting in significant overprovisioning and high costs. Which action should the SysOps administrator take to prevent this overprovisioning?

  1. A
    Increase the default cooldown period of the Auto Scaling group to 300300 seconds.
  2. B
    Enable detailed monitoring on the Amazon EC2 launch template to increase the CloudWatch metric granularity to 11-minute intervals.
  3. Increase the estimated instance warmup time in the target tracking scaling policy to 300300 seconds.Answer
  4. D
    Configure an Amazon EC2 Auto Scaling lifecycle hook to keep the new instances in the `Pending:Wait` state for 55 minutes.

Answer

Increase the estimated instance warmup time in the target tracking scaling policy to 300300 seconds.
Increasing the estimated instance warmup time to 300300 seconds is correct because target tracking scaling policies ignore the default cooldown period of the Auto Scaling group and rely entirely on the estimated instance warmup. Setting this warmup period to match the 55-minute bootstrapping time ensures that the group waits for new instances to start processing traffic and contributing to metrics before evaluating whether to scale out again.

Step-by-Step Solution

1
Identify the type of scaling policy in use and how it handles new instance metrics.
The Auto Scaling group uses a target tracking scaling policy, which relies on the estimated instance warmup parameter.
Target tracking policies ignore the default cooldown period of the Auto Scaling group and rely on instance warmup to determine when new instances should contribute to metric calculations.
2
Analyze the impact of the bootstrapping delay on the scaling metrics.
The newly launched instances take 55 minutes (300300 seconds) to become ready. During this time, average CPU utilization remains high because the new instances are not yet handling load.
If the estimated instance warmup is shorter than 55 minutes, the policy assumes the new instances are fully warmed up and incorrectly concludes that more capacity is needed, leading to overscaling.
3
Adjust the scaling configuration to match the bootstrapping time.
Setting the estimated instance warmup to 300300 seconds (55 minutes) prevents the policy from triggering additional launches until the newly launched instances have finished bootstrapping.
This aligns the scaling policy's metric evaluation delay with the actual initialization time of the instances.

Key Concept

Instance warmup configuration in EC2 Auto Scaling target tracking policies
Estimated Time:1m 30s
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Topics

Auto Scaling and Elasticity

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