Auto scaling App Service in Azure - Step-by-Step Execution

Process Flow - Auto scaling App Service

Start: App Service Running

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Monitor Metrics: CPU, Requests

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Check Thresholds

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Scale Out

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Add Instances

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Update App Service Instances

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Continue Monitoring

The App Service monitors its performance metrics. If usage is high, it adds instances (scale out). If usage is low, it removes instances (scale in). This cycle repeats to keep the app responsive.

Execution Sample

Azure

Monitor CPU > 70%?
  Yes -> Increase instances by 1
Monitor CPU < 30%?
  Yes -> Decrease instances by 1
Else -> No change

This logic checks CPU usage and adjusts the number of App Service instances accordingly.

Process Table

Step	CPU Usage (%)	Condition Checked	Action Taken	Instances Count
1	65	CPU > 70%? No	No change	2
2	75	CPU > 70%? Yes	Scale Out +1	3
3	80	CPU > 70%? Yes	Scale Out +1	4
4	50	CPU < 30%? No	No change	4
5	25	CPU < 30%? Yes	Scale In -1	3
6	20	CPU < 30%? Yes	Scale In -1	2
7	35	CPU < 30%? No	No change	2
8	72	CPU > 70%? Yes	Scale Out +1	3
9	68	CPU > 70%? No	No change	3
10	28	CPU < 30%? Yes	Scale In -1	2

💡 Execution stops after 10 steps of monitoring and scaling decisions.

Status Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5	After 6	After 7	After 8	After 9	After 10
CPU Usage (%)	65	75	80	50	25	20	35	72	68	28	N/A
Instances Count	2	2	3	4	4	3	2	2	3	3	2

Key Moments - 3 Insights

Why does the number of instances not change when CPU usage is 65%?

Because the condition to scale out requires CPU usage to be greater than 70%, which is false at 65% (see step 1 in execution_table). So no scaling action is taken.

Why do we scale in when CPU usage is 25% but not when it is 35%?

Scaling in happens only if CPU usage is less than 30%. At 25% (step 5), this is true, so instances decrease. At 35% (step 7), the condition is false, so no change occurs.

Can the instances count go below 1 during scaling in?

No, best practice is to keep at least one instance running to avoid downtime. The example keeps instances at minimum 2, never scaling below that.

Visual Quiz - 3 Questions

Look at the execution_table at step 3. What is the instances count after scaling?

A 2

B 3

C 4

D 5

💡 Hint

Check the 'Instances Count' column at step 3 in execution_table.

At which step does the CPU usage first trigger a scale in action?

A Step 5

B Step 4

C Step 6

D Step 7

💡 Hint

Look for the first 'Scale In' action in the 'Action Taken' column in execution_table.

If the CPU threshold for scaling out changed from 70% to 60%, what would happen at step 1?

A No change, instances remain 2

B Scale Out, instances increase to 3

C Scale In, instances decrease to 1

D Error in scaling

💡 Hint

Compare CPU usage at step 1 with new threshold and check scaling condition in execution_table.

Concept Snapshot

Auto scaling App Service:
- Monitors app metrics like CPU usage.
- Scales out (adds instances) if usage > threshold.
- Scales in (removes instances) if usage < threshold.
- Keeps minimum instances to avoid downtime.
- Continuously adjusts to keep app responsive.

Full Transcript

Auto scaling in Azure App Service means the system watches how busy your app is, like checking CPU usage. If the app gets busy (CPU over 70%), it adds more instances to handle the load. If the app is not busy (CPU under 30%), it removes instances to save resources. This process repeats continuously to keep your app running smoothly without manual intervention. The example shows CPU usage changing over time and how the number of instances adjusts accordingly, never going below a safe minimum.