A SysOps Administrator has implemented an Auto Scaling group with a step scaling policy. The Administrator notices that the additional instances have not been included in the aggregated metrics. Why…

Question

Options

• AThe warm-up period has not expired
• BThe instances are still in the boot process
• CThe instances have not been attached to the Auto Scaling group
• DThe instances are included in a different set of metrics

• A
  4% (1)
• B
  91% (21)
• D
  4% (1)

Explanation

Note: The stated correct answer (B) appears to be incorrect from an AWS technical standpoint. Option A is actually the correct answer for this scenario, and here's why:

When a step scaling policy launches new instances, AWS Auto Scaling intentionally excludes those instances from the aggregated CloudWatch metrics until the configured instance warm-up period expires. This prevents the scaling alarm from firing prematurely and over-provisioning - the warm-up period is the specific mechanism that gates metric aggregation.

Why the distractors are wrong:

• B (boot process) - While booting instances can't send metrics, this isn't the Auto Scaling–specific mechanism being tested. Instances enter InService state during/after boot, but the warm-up period is what controls metric inclusion in step scaling.
• C (not attached to ASG) - Instances launched by the ASG are automatically attached; this scenario doesn't apply.
• D (different metrics set) - Auto Scaling uses a unified aggregated metric; there's no separate metrics set for new instances.

Memory tip: Think of the warm-up period as a "probation window" - a new hire (instance) is on the floor (InService) but not yet counted in the team's productivity metrics (aggregated CloudWatch) until probation (warm-up) ends. If you see a step scaling question about missing metrics, warm-up period is almost always the answer.

If this question is from a practice exam, the answer key may contain an error - double-check against the AWS Step Scaling documentation.

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