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Difficulty: EasyAuto Scaling and Elasticity

An Auto Scaling group uses a target tracking scaling policy based on average CPU utilization. During sudden load increases, the Auto Scaling group launches new EC2 instances. The application on these instances requires five minutes to complete initialization and begin serving requests. During this initialization period, the Auto Scaling group continues to launch additional, unnecessary EC2 instances because the average CPU utilization remains high. Which parameter should be configured to prevent this behavior?

  1. The default instance warmup time on the Auto Scaling groupAnswer
  2. B
    The scale-in cooldown period on the target tracking policy
  3. C
    Detailed monitoring for the EC2 instances in the launch template
  4. D
    The EventBridge rule delay timer for Auto Scaling group events

Answer

The default instance warmup time on the Auto Scaling group
Configuring the default instance warmup time tells the Auto Scaling group to exclude newly launched instances from the group's metric averages until they have warmed up for the specified duration. This prevents the scaling policy from launching additional instances while the first set of instances is still initializing.

Step-by-Step Solution

1
Identify the cause of the unnecessary scaling actions.
Newly launched instances are taking 5 minutes to boot, but their high initialization CPU utilization is being immediately included in the group average calculation, triggering further scale-out.
This helps locate the phase of the lifecycle where the problem occurs.
2
Determine the parameter that controls how long to wait before including new instances in Auto Scaling metrics.
The default instance warmup parameter (or policy-specific warmup) defines this exclusion window.
To choose the setting that directly pauses metric aggregation for booting instances.

Key Concept

Auto Scaling target tracking and instance warmup configuration
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Topics

Auto Scaling and Elasticity

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