Auto Scaling groups in AWS - Commands & Configuration

Introduction

Auto Scaling groups help keep your app running smoothly by automatically adding or removing servers based on how busy your app is. This means your app can handle more visitors without crashing and save money when fewer servers are needed.

When your website gets more visitors during the day and fewer at night, and you want to adjust servers automatically.

When you want to replace servers that stop working without manual effort.

When you want to save money by running only the number of servers needed at any time.

When you want to make sure your app stays available even if some servers fail.

When you want to test how your app behaves under different loads by scaling servers up and down.

Config File - asg-configuration.json

asg-configuration.json

{
  "AutoScalingGroupName": "example-asg",
  "LaunchConfigurationName": "example-launch-config",
  "MinSize": 1,
  "MaxSize": 3,
  "DesiredCapacity": 2,
  "AvailabilityZones": ["us-east-1a", "us-east-1b"],
  "Tags": [
    {
      "Key": "Name",
      "Value": "example-instance",
      "PropagateAtLaunch": true
    }
  ]
}

This JSON file defines an Auto Scaling group named example-asg. It uses a launch configuration called example-launch-config to create servers. The group keeps at least 1 server running and can scale up to 3 servers. It tries to keep 2 servers running by default. The servers will be launched in two availability zones for reliability. The tag Name=example-instance helps identify the servers.

Commands

This command creates a launch configuration named example-launch-config. It tells AWS what kind of server to launch, using a specific image and instance type.

Terminal

aws autoscaling create-launch-configuration --launch-configuration-name example-launch-config --image-id ami-0c94855ba95c71c99 --instance-type t2.micro

Expected Output

No output (command runs silently)

→

--launch-configuration-name - Names the launch configuration for reuse in Auto Scaling groups

→

--image-id - Specifies the server image to use

→

--instance-type - Specifies the size and power of the server

This command creates the Auto Scaling group named example-asg using the launch configuration. It sets the minimum, maximum, and desired number of servers and specifies the zones where servers will run. It also adds a tag to identify the servers.

Terminal

aws autoscaling create-auto-scaling-group --auto-scaling-group-name example-asg --launch-configuration-name example-launch-config --min-size 1 --max-size 3 --desired-capacity 2 --availability-zones us-east-1a us-east-1b --tags Key=Name,Value=example-instance,PropagateAtLaunch=true

Expected Output

No output (command runs silently)

→

--auto-scaling-group-name - Names the Auto Scaling group

→

--min-size - Minimum number of servers to keep running

→

--max-size - Maximum number of servers allowed

→

--desired-capacity - Number of servers to start with

This command checks the details of the Auto Scaling group to confirm it was created correctly and see its current state.

Terminal

aws autoscaling describe-auto-scaling-groups --auto-scaling-group-names example-asg

Expected Output

{

    "AutoScalingGroups": [

        {

            "AutoScalingGroupName": "example-asg",

            "LaunchConfigurationName": "example-launch-config",

            "MinSize": 1,

            "MaxSize": 3,

            "DesiredCapacity": 2,

            "AvailabilityZones": [

                "us-east-1a",

                "us-east-1b"

            ],

            "Instances": [],

            "Tags": [

                {

                    "Key": "Name",

                    "Value": "example-instance",

                    "PropagateAtLaunch": true

                }

            ]

        }

    ]

}

→

--auto-scaling-group-names - Specifies which Auto Scaling group to describe

This command changes the desired number of servers to 3, telling AWS to add one more server to handle more traffic.

Terminal

aws autoscaling update-auto-scaling-group --auto-scaling-group-name example-asg --desired-capacity 3

Expected Output

No output (command runs silently)

→

--desired-capacity - Sets the new target number of servers

This command deletes the Auto Scaling group and all its servers immediately, cleaning up resources when you no longer need them.

Terminal

aws autoscaling delete-auto-scaling-group --auto-scaling-group-name example-asg --force-delete

Expected Output

No output (command runs silently)

→

--force-delete - Deletes the group even if it has running servers

Key Concept

If you remember nothing else from this pattern, remember: Auto Scaling groups automatically adjust the number of servers to keep your app running well and save money.

Common Mistakes

Not creating a launch configuration before creating the Auto Scaling group

The Auto Scaling group needs a launch configuration to know what kind of servers to create, so it will fail without one.

Always create a launch configuration first with the desired server settings before creating the Auto Scaling group.

Setting min-size higher than max-size

This causes a conflict and the Auto Scaling group will not work properly because it cannot keep more servers than the maximum allowed.

Ensure min-size is less than or equal to max-size when creating or updating the group.

Not specifying availability zones

Without availability zones, the Auto Scaling group cannot launch servers in the right places, which may cause failures or poor availability.

Always specify at least one availability zone when creating the Auto Scaling group.

Summary

Create a launch configuration to define the server type and image.

Create an Auto Scaling group using the launch configuration, setting min, max, and desired server counts.

Check the Auto Scaling group details to confirm setup.

Update the desired capacity to scale servers up or down as needed.

Delete the Auto Scaling group when it is no longer needed.

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