VM Scale Sets for auto scaling in Azure - Step-by-Step Execution

Process Flow - VM Scale Sets for auto scaling

Start VM Scale Set

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Monitor Metrics

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Check Scale Rules

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Scale Out

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Add VM Instances

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Update Load Balancer

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Continue Monitoring

The VM Scale Set starts and monitors performance metrics. If rules say to scale out, it adds VM instances and updates the load balancer, then continues monitoring.

Execution Sample

Azure

1. Create VM Scale Set with 2 VMs
2. Monitor CPU usage
3. If CPU > 70%, add 1 VM
4. If CPU < 30%, remove 1 VM
5. Repeat monitoring

This setup automatically adds or removes VM instances based on CPU usage thresholds.

Process Table

Step	CPU Usage (%)	Current VM Count	Condition	Action Taken	Resulting VM Count
1	50	2	50 > 70? No	No scaling	2
2	75	2	75 > 70? Yes	Scale out: add 1 VM	3
3	65	3	65 > 70? No	No scaling	3
4	25	3	25 < 30? Yes	Scale in: remove 1 VM	2
5	40	2	40 < 30? No	No scaling	2
6	80	2	80 > 70? Yes	Scale out: add 1 VM	3
7	85	3	85 > 70? Yes	Scale out: add 1 VM	4
8	60	4	60 > 70? No	No scaling	4
9	20	4	20 < 30? Yes	Scale in: remove 1 VM	3
10	30	3	30 < 30? No	No scaling	3

💡 Monitoring stops after step 10; scaling decisions made based on CPU thresholds.

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 (%)	N/A	50	75	65	25	40	80	85	60	20	30
VM Count	2	2	3	3	2	2	3	4	4	3	3

Key Moments - 3 Insights

Why does the VM count not change when CPU usage is 50% at step 1?

Because 50% is not greater than the scale-out threshold of 70%, so no scaling action is taken as shown in execution_table row 1.

Why does the VM count decrease at step 4 when CPU usage is 25%?

Because 25% is below the scale-in threshold of 30%, triggering removal of one VM instance as shown in execution_table row 4.

Why are multiple scale-outs possible in consecutive steps like 6 and 7?

Because CPU usage remains above 70%, each check triggers adding one VM, increasing VM count step by step as shown in execution_table rows 6 and 7.

Visual Quiz - 3 Questions

Look at the execution table, what is the VM count after step 3?

A 2

B 3

C 4

D 1

💡 Hint

Check the 'Resulting VM Count' column at step 3 in the execution_table.

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

A Step 2

B Step 6

C Step 4

D Step 9

💡 Hint

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

If the scale-out threshold changed from 70% to 80%, what would happen at step 2?

A No scaling would happen

B Scale in would happen

C Scale out would still happen

D VM count would decrease

💡 Hint

Compare CPU usage at step 2 with the new threshold and check the 'Condition' column.

Concept Snapshot

VM Scale Sets automatically add or remove VM instances based on performance metrics.
Set thresholds (e.g., CPU > 70% to scale out, CPU < 30% to scale in).
Monitor metrics continuously.
Scale out adds VMs; scale in removes VMs.
Load balancer updates to distribute traffic.
This ensures apps handle demand efficiently.

Full Transcript

VM Scale Sets start with a set number of VMs. They monitor CPU usage regularly. If CPU usage goes above 70%, the system adds one VM to handle more load. If CPU usage falls below 30%, it removes one VM to save resources. This process repeats, adjusting the number of VMs to match demand. The load balancer updates to include new VMs or exclude removed ones. This automatic scaling helps keep applications responsive and cost-effective.