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Difficulty: MediumConfigure Azure App Service Web Apps

An operations team is configuring autoscale rules for an Azure App Service Plan hosting a web application. They define the following rules:

* Scale-out Rule 1: Increase the instance count by 1 if the average CPU Percentage is greater than 80%.
* Scale-out Rule 2: Increase the instance count by 1 if the average Memory Percentage is greater than 85%.
* Scale-in Rule 1: Decrease the instance count by 1 if the average CPU Percentage is less than 40%.
* Scale-in Rule 2: Decrease the instance count by 1 if the average Memory Percentage is less than 50%.

Under which condition will the App Service Plan scale in?

  1. Only when the CPU Percentage is less than 40% and the Memory Percentage is less than 50%Answer
  2. B
    When either the CPU Percentage is less than 40% or the Memory Percentage is less than 50%
  3. C
    When the average of the CPU Percentage and Memory Percentage is less than 45%
  4. D
    When the CPU Percentage is less than 40%, regardless of the Memory Percentage

Answer

Only when the CPU Percentage is less than 40% and the Memory Percentage is less than 50%
In Azure Monitor autoscale engine, when multiple scale-in rules are defined, they are evaluated using a logical AND operation. This means the autoscale engine will only decrease the instance count if all scale-in conditions are met. In this scenario, both the CPU Percentage must be below 40% and the Memory Percentage must be below 50% for scale-in to occur.

Step-by-Step Solution

1
Identify the scale-out evaluation logic in Azure Autoscale.
Multiple scale-out rules are combined using a logical OR operator (scaling out if any rule is met).
This is the default engine behavior designed to prioritize application performance under load.
2
Identify the scale-in evaluation logic in Azure Autoscale.
Multiple scale-in rules are combined using a logical AND operator (scaling in only if all rules are met).
This prevents premature scale-in events that could degrade performance if one metric is still high.
3
Apply the scale-in logic to the configured rules.
Scale-in will trigger only when both CPU Percentage is less than 40% AND Memory Percentage is less than 50%.
Both conditions must evaluate to true simultaneously to satisfy the logical AND requirement.

Key Concept

Azure App Service Autoscale Rule Evaluation Logic
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Topics

Configure Azure App Service Web Apps

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