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Difficulty: MediumConfigure Virtual Machine Scale Sets (VMSS)

An administrator is configuring autoscaling for an Azure Virtual Machine Scale Set (VMSS) named `vmss-commerce`. The web application hosted on the scale set experiences rapid traffic fluctuations. To prevent rapid, continuous scaling actions (thrashing), which of the following settings should you configure? (Select TWO)

  1. Set a cool-down period of 10 minutes or more to allow the system to stabilize before subsequent scale actions.Answer
  2. Maintain a wide margin between the scale-out (80%) and scale-in (30%) CPU thresholds.Answer
  3. C
    Configure the scale-out rule to use the Maximum metric aggregation and a 1-minute duration.
  4. D
    Set the scale-in rule to run immediately without a cool-down period to minimize costs.

Answer

To prevent thrashing in a Virtual Machine Scale Set, you should configure an adequate cool-down period and maintain a wide margin between the scale-out and scale-in thresholds.
Configuring a cool-down period ensures the system waits for the metrics to stabilize after a scale event before taking another action. Additionally, keeping a wide margin between scale-out (80%) and scale-in (30%) thresholds prevents the addition of a new instance from immediately lowering the average CPU level enough to trigger a scale-in operation.

Step-by-Step Solution

1
Analyze the scaling thresholds to ensure the scale-out and scale-in values are not too close, avoiding situations where adding an instance reduces the load per instance enough to immediately trigger a scale-in.
You identify that a wide margin (such as 80% for scale-out and 30% for scale-in) prevents immediate reverse actions.
This establishes a stable operating range for the scale set.
2
Configure the cool-down period setting on both the scale-out and scale-in rules.
The scale set waits for the specified duration (e.g., 10 minutes) after any scaling event before evaluating the metrics again.
This allows new instances time to start up and begin processing load, ensuring the metrics reflect the new state of the scale set before further scaling occurs.

Key Concept

Instance thrashing in Virtual Machine Scale Sets occurs when scale-out and scale-in actions trigger continuously in a loop. To mitigate this, administrators must configure appropriate cool-down durations and maintain a sufficient gap between scale-out and scale-in metric thresholds.
Estimated Time:1m 30s
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Topics

Configure Virtual Machine Scale Sets (VMSS)

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