Auto Scaling groups in AWS - Mini Project: Build & Apply

Auto Scaling Groups Setup in AWS

📖 Scenario: You are managing a web application hosted on AWS. To handle varying traffic, you want to automatically add or remove servers based on demand. This helps keep the app fast and saves money when traffic is low.

🎯 Goal: Create an AWS Auto Scaling group configuration that launches EC2 instances using a launch template. Set the minimum, maximum, and desired number of instances to control scaling.

📋 What You'll Learn

Create a launch template named MyLaunchTemplate with a specified AMI ID and instance type.

Create an Auto Scaling group named MyAutoScalingGroup using the launch template.

Set the Auto Scaling group minimum size to 1, maximum size to 3, and desired capacity to 2.

Attach the Auto Scaling group to a specified VPC subnet.

💡 Why This Matters

🌍 Real World

Auto Scaling groups help websites and applications handle changing traffic by automatically adjusting the number of servers running.

💼 Career

Cloud engineers and DevOps professionals use Auto Scaling groups to ensure applications are reliable, cost-effective, and responsive to user demand.

1

Create the Launch Template

Create a launch template named MyLaunchTemplate with the AMI ID ami-0abcdef1234567890 and instance type t3.micro.

AWS

# Create a launch template named MyLaunchTemplate
# Your code here

Hint

The launch template defines the AMI and instance type for your servers.

2

Define Auto Scaling Group Basic Settings

Create an Auto Scaling group named MyAutoScalingGroup using the launch template MyLaunchTemplate. Set the minimum size to 1, maximum size to 3, and desired capacity to 2.

AWS

resource "aws_launch_template" "MyLaunchTemplate" {
  name_prefix   = "MyLaunchTemplate"
  image_id      = "ami-0abcdef1234567890"
  instance_type = "t3.micro"
}

# Create Auto Scaling group MyAutoScalingGroup with min=1, max=3, desired=2
# Your code here

Hint

Use the launch template ID and set the size parameters for the Auto Scaling group.

3

Attach Auto Scaling Group to VPC Subnet

Add the subnet ID subnet-12345678 to the Auto Scaling group MyAutoScalingGroup so instances launch in this subnet.

AWS

resource "aws_launch_template" "MyLaunchTemplate" {
  name_prefix   = "MyLaunchTemplate"
  image_id      = "ami-0abcdef1234567890"
  instance_type = "t3.micro"
}

resource "aws_autoscaling_group" "MyAutoScalingGroup" {
  name                      = "MyAutoScalingGroup"
  max_size                  = 3
  min_size                  = 1
  desired_capacity          = 2
  launch_template {
    id      = aws_launch_template.MyLaunchTemplate.id
    version = "$Latest"
  }
  # Add subnet_ids here
  # Your code here
}

Hint

Use the vpc_zone_identifier attribute with a list containing the subnet ID.

4

Enable Health Check Grace Period

Add a health check grace period of 300 seconds to the Auto Scaling group MyAutoScalingGroup to allow instances time to start before health checks.

AWS

resource "aws_launch_template" "MyLaunchTemplate" {
  name_prefix   = "MyLaunchTemplate"
  image_id      = "ami-0abcdef1234567890"
  instance_type = "t3.micro"
}

resource "aws_autoscaling_group" "MyAutoScalingGroup" {
  name                      = "MyAutoScalingGroup"
  max_size                  = 3
  min_size                  = 1
  desired_capacity          = 2
  launch_template {
    id      = aws_launch_template.MyLaunchTemplate.id
    version = "$Latest"
  }
  vpc_zone_identifier = ["subnet-12345678"]
  # Add health_check_grace_period here
  # Your code here
}

Hint

This setting helps avoid false health check failures during instance startup.

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