Azure Web App Autoscaling: Identifying Scale-In Utilizations

Identifying Scale-In Utilizations

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Question

You have an Azure web app named App1 that is configured to run between two and five instances. There are currently three instances of App1 running.

App1 has the following autoscale rules:

-> Increase the instance count by one when the CPU percentage is greater or equal to 80.

-> Decrease the instance count by one when the CPU percentage is less than or equal to 60.

You are evaluating the following CPU percentage of utilization for App1:

-> 60%

-> 55%

-> 50%

-> 45%

You need to identify which utilizations will cause App1 to scale in.

Answers

A. 45% only

B. 45% and 50% only

C. 50% and 55% only

D. 45%, 50%, and 55% only

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Explanations

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A. B. C. D.

Azure Monitor autoscaling allows you to scale the number of running instances up or down, based on telemetry data (metrics). Scale-in occurs when the instances are decrease. For this rule the instances are decreased when the CPU usage is 60% or lower.

https://docs.microsoft.com/en-us/azure/azure-monitor/platform/autoscale-custom-metric https://docs.microsoft.com/en-us/azure/azure-monitor/platform/autoscale-common-metrics

To identify the utilizations that will cause App1 to scale in, we need to understand how autoscaling works based on the defined rules. The autoscale rules for App1 are:

Increase the instance count by one when the CPU percentage is greater or equal to 80.
Decrease the instance count by one when the CPU percentage is less than or equal to 60.

There are currently three instances of App1 running, and the configuration allows for a minimum of two and a maximum of five instances.

Now, let's evaluate the CPU percentage of utilization for App1:

60%: This is the upper threshold for scaling in, as the current instance count of three is within the desired range. Therefore, this utilization will not cause App1 to scale in.
55%: This is below the scaling threshold, so it will not cause App1 to scale in.
50%: This is below the scaling threshold, so it will not cause App1 to scale in.
45%: This is below the scaling threshold, and it is also below the lower threshold for scaling out. Therefore, this utilization will cause App1 to scale in by decreasing the instance count by one.

Based on the above evaluation, the utilizations that will cause App1 to scale in are 45%, and the answer is A. 45% only. Utilizations of 50% and 55% do not meet the scaling criteria, and 60% is the upper threshold for scaling in.

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