Auto Scaling groups in AWS - Step-by-Step Execution

Process Flow - Auto Scaling groups

Start: Define Auto Scaling Group

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Set Desired Capacity

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Monitor Metrics (CPU, Network, etc.)

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Check Scaling Policy

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Add Instances

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Maintain Desired Capacity

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Repeat

Auto Scaling groups start with a desired number of instances, monitor performance, and add or remove instances automatically to keep the system balanced.

Execution Sample

AWS

Create ASG with desired=2
Monitor CPU > 70%
Scale up by 1
Monitor CPU < 30%
Scale down by 1

This simulates an Auto Scaling group that starts with 2 instances, adds one if CPU is high, and removes one if CPU is low.

Process Table

Step	Current Instances	CPU Usage	Condition	Action	Resulting Instances
1	2	65%	CPU > 70%? No	No scaling	2
2	2	75%	CPU > 70%? Yes	Scale up by 1	3
3	3	80%	CPU > 70%? Yes	Scale up by 1	4
4	4	50%	CPU < 30%? No	No scaling	4
5	4	25%	CPU < 30%? Yes	Scale down by 1	3
6	3	20%	CPU < 30%? Yes	Scale down by 1	2
7	2	40%	CPU < 30%? No	No scaling	2

💡 CPU usage stabilizes between thresholds, no further scaling needed.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5	After Step 6	After Step 7
Current Instances	2	2	3	4	4	3	2	2
CPU Usage	65%	65%	75%	80%	50%	25%	20%	40%

Key Moments - 3 Insights

Why does the number of instances increase when CPU is above 70%?

Because the scaling policy triggers adding instances to handle higher load, as shown in steps 2 and 3 in the execution_table.

Why does the number of instances decrease when CPU is below 30%?

To save resources, the Auto Scaling group removes instances when CPU is low, as seen in steps 5 and 6.

Why does the number of instances stay the same at step 7 even though CPU changed?

Because CPU usage is 40%, which is between the thresholds, so no scaling action is needed (step 7 in execution_table).

Visual Quiz - 3 Questions

Look at the execution_table, how many instances are running after step 3?

A 4

B 2

C 3

D 5

💡 Hint

Check the 'Resulting Instances' column at step 3.

At which step does the Auto Scaling group first remove an instance?

A Step 4

B Step 5

C Step 6

D Step 7

💡 Hint

Look for the first 'Scale down by 1' action in the 'Action' column.

If the CPU threshold for scaling up changed to 80%, what would happen at step 2?

A Scale up by 1

B Scale down by 1

C No scaling

D Scale up by 2

💡 Hint

Compare CPU usage at step 2 with the new threshold.

Concept Snapshot

Auto Scaling groups keep your app running smoothly by adding or removing servers automatically.
You set a desired number of servers and rules based on metrics like CPU.
If CPU is high, it adds servers; if low, it removes servers.
This helps handle traffic changes without manual work.
Always set sensible thresholds to avoid too many changes.

Full Transcript

Auto Scaling groups start with a set number of servers called instances. They watch how busy these servers are using metrics like CPU usage. When the CPU goes above a set limit, the group adds more servers to help handle the load. When CPU drops below a lower limit, it removes servers to save resources. This process repeats to keep the system balanced and efficient. For example, starting with 2 servers, if CPU goes above 70%, one server is added. If CPU falls below 30%, one server is removed. This automatic adjustment helps your app stay fast and cost-effective.