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

Process Flow - Auto Scaling groups

Start: Define Auto Scaling Group

↓

Set Desired Capacity

↓

Monitor Metrics (CPU, Network, etc.)

↓

Check Scaling Policy

↓

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.

Practice

1. What is the main purpose of an Auto Scaling group in AWS?

easy

A. To store data in a scalable database

B. To manage user access and permissions

C. To automatically adjust the number of servers based on demand

D. To monitor network traffic for security threats

Solution

1. Step 1: Understand Auto Scaling group function

   An Auto Scaling group automatically changes the number of servers to match demand.

2. Step 2: Compare options to this function

   Only To automatically adjust the number of servers based on demand describes automatic adjustment of servers based on demand.

3. Final Answer:

   To automatically adjust the number of servers based on demand -> Option C

4. Quick Check:

   Auto Scaling = Adjust servers automatically [OK]

Hint: Auto Scaling groups adjust servers automatically [OK]

Common Mistakes:

• Confusing Auto Scaling with database services
• Thinking Auto Scaling manages user permissions
• Assuming Auto Scaling monitors security

2. Which of the following is the correct way to set the minimum size of an Auto Scaling group using AWS CLI?

easy

A. aws autoscaling set-minimum --group my-asg --size 2

B. aws autoscaling update-auto-scaling-group --auto-scaling-group-name my-asg --min-size 2

C. aws autoscaling create-auto-scaling-group --min 2 --name my-asg

D. aws autoscaling configure-group --asg my-asg --minimum 2

Solution

1. Step 1: Recall AWS CLI command for updating Auto Scaling group

   The correct command to update settings is 'update-auto-scaling-group' with parameters for group name and min size.

2. Step 2: Check each option's syntax

   aws autoscaling update-auto-scaling-group --auto-scaling-group-name my-asg --min-size 2 uses correct command and parameters. Others use invalid commands or parameters.

3. Final Answer:

   aws autoscaling update-auto-scaling-group --auto-scaling-group-name my-asg --min-size 2 -> Option B

4. Quick Check:

   Update Auto Scaling group with correct CLI syntax [OK]

Hint: Use 'update-auto-scaling-group' to change min size [OK]

Common Mistakes:

• Using create command instead of update
• Wrong parameter names like --min or --minimum
• Incorrect command verbs like set-minimum or configure-group

3. Given this Auto Scaling group configuration:
MinSize=1, MaxSize=3, DesiredCapacity=2
What happens if the load increases and the group scales out to 3 instances, then the load drops suddenly?

medium

A. The group will scale in to 1 instance, respecting MinSize

B. The group will keep 3 instances running regardless of load

C. The group will scale in to 0 instances

D. The group will scale in to 2 instances, the DesiredCapacity

Solution

1. Step 1: Understand scaling limits

   MinSize=1 means the group will never go below 1 instance, MaxSize=3 means it can scale up to 3.

2. Step 2: Analyze behavior on load drop

   When load drops, Auto Scaling reduces instances but not below MinSize, so it scales down to 1.

3. Final Answer:

   The group will scale in to 1 instance, respecting MinSize -> Option A

4. Quick Check:

   MinSize limits minimum instances [OK]

Hint: MinSize sets the lowest number of instances [OK]

Common Mistakes:

• Thinking DesiredCapacity is fixed after scaling
• Assuming scaling can go below MinSize
• Believing MaxSize limits minimum instances

4. You wrote this snippet to create an Auto Scaling group but it fails:

aws autoscaling create-auto-scaling-group --auto-scaling-group-name my-asg --min-size 2 --max-size 1 --desired-capacity 1 --launch-configuration-name my-launch-config --vpc-zone-identifier subnet-12345

What is the error?

medium

A. VPC subnet ID is invalid

B. DesiredCapacity cannot be less than MinSize

C. Launch configuration name is missing

D. MinSize cannot be greater than MaxSize

Solution

1. Step 1: Check size parameters

   MinSize is set to 2, MaxSize is set to 1, which is invalid because MinSize must be less than or equal to MaxSize.

2. Step 2: Validate other parameters

   DesiredCapacity is 1, which is allowed if between MinSize and MaxSize, but here MinSize > MaxSize causes failure.

3. Final Answer:

   MinSize cannot be greater than MaxSize -> Option D

4. Quick Check:

   MinSize ≤ MaxSize rule violated [OK]

Hint: MinSize must be ≤ MaxSize to create group [OK]

Common Mistakes:

• Setting MinSize higher than MaxSize
• Ignoring error messages about sizes
• Assuming DesiredCapacity fixes size conflicts

5. You want an Auto Scaling group that maintains at least 2 instances, scales up to 5 during high load, and automatically replaces unhealthy instances. Which configuration achieves this?

hard

A. Set MinSize=2, MaxSize=5, DesiredCapacity=2, enable health checks and instance replacement

B. Set MinSize=5, MaxSize=2, DesiredCapacity=3, disable health checks

C. Set MinSize=0, MaxSize=5, DesiredCapacity=5, no health checks

D. Set MinSize=2, MaxSize=5, DesiredCapacity=5, disable instance replacement

Solution

1. Step 1: Define scaling limits

   MinSize=2 ensures at least 2 instances, MaxSize=5 allows scaling up to 5.

2. Step 2: Set desired capacity and health checks

   DesiredCapacity=2 starts with 2 instances. Enabling health checks and instance replacement ensures unhealthy instances are replaced automatically.

3. Step 3: Evaluate other options

   The other options either have invalid MinSize/MaxSize, disable health checks, or disable instance replacement.

4. Final Answer:

   Set MinSize=2, MaxSize=5, DesiredCapacity=2, enable health checks and instance replacement -> Option A

5. Quick Check:

   Correct scaling limits and health checks enabled [OK]

Hint: MinSize ≤ DesiredCapacity ≤ MaxSize with health checks enabled [OK]

Common Mistakes:

• Setting MinSize greater than MaxSize
• Disabling health checks or instance replacement
• Setting DesiredCapacity outside Min/Max range