Dynamically Adjusting Auto Scaling Group Size with AWS Lambda

In dynamic cloud environments, applications often require scaling to handle varying workloads. AWS Auto Scaling groups are a powerful tool for this purpose, automatically adjusting the number of instances to maintain performance. However, there are times when you might need to manually adjust the size of your Auto Scaling group. This blog post will guide you through the process of creating an AWS Lambda function to increase or decrease the minimum size of an Auto Scaling group on demand.

Prerequisites

Before we dive into the implementation, ensure you have the following:

1. AWS Account: You need an AWS account to access AWS services.
2. IAM Role for Lambda: Create an IAM role with the necessary permissions for AWS Lambda to interact with Auto Scaling groups.
3. Auto Scaling Group: An existing Auto Scaling group that you want to manage.

Lambda Function

First, set up an environment variable ASG_NAME which holds the ID of your ‘Autoscaling group’ distribution. This can be done in the Lambda console under the "Configuration" tab or through the AWS CLI.

import boto3

def lambda_handler(event, context):
    print(event);
    action = event.get('resource', '')
    asg_name = os.getenv('ASG_NAME')
    autoscaling = boto3.client('autoscaling')
    
    response = autoscaling.describe_auto_scaling_groups(AutoScalingGroupNames=[asg_name])
    current_min_size = response['AutoScalingGroups'][0]['MinSize']

    if 'increase' in action:
        new_min_size = current_min_size + 1
    elif 'decrease' in action:
        if current_min_size == 1:
            return {
                'statusCode': 400,
                'body': 'Minimum size is already 1 and changing to 0 is not recommended in production workloads'
            }
        else:
            new_min_size = current_min_size - 1
    else:
        return {
            'statusCode': 400,
            'body': 'Invalid action. Valid actions are "increase" or "decrease".'
        }
    
    response = autoscaling.update_auto_scaling_group(
        AutoScalingGroupName=asg_name,
        MinSize=new_min_size
    )
    
    return {
        'statusCode': 200,
        'body': f'Successfully updated minimum size to {new_min_size}'
    }

Deploying the Lambda Function

1. Create a new Lambda function in the AWS Management Console.
2. Assign the necessary IAM role to your Lambda function. This role should have permissions to describe and update Auto Scaling groups.
3. Deploy the function code by copying the provided Python script into the Lambda code editor or by uploading a ZIP file.

Integrating with Other AWS Services

integrate this Lambda function with AWS API Gateway. This enables you to trigger the function based on specific events or expose it as an HTTP endpoint. With increase and decrease Routers.
 

1. Open the API Gateway service in the AWS Management Console.
2. Click on “Create API” and choose “HTTP API”.
3. Add a new route for starting the Auto Scaling Group:

• Resource path: /decrease

1. Add another route for stopping the Auto Scaling Group:

• Resource path: /increase

1. For both routes, set the integration target to your Lambda function.

https://<your-api-id>.execute-api.<region>.amazonaws.com/increase

https://<your-api-id>.execute-api.<region>.amazonaws.com/decrease

Conclusion

By following these steps, you’ve created a Lambda function that can dynamically adjust the minimum size of your Auto Scaling group. This solution provides flexibility in managing your application’s scalability and ensures you can handle varying workloads efficiently. Whether you’re automating scale adjustments or providing manual overrides, this Lambda function is a valuable addition to your AWS toolkit.

Take control of your application’s scalability by implementing this Lambda function today! Follow the steps outlined in the blog to effortlessly adjust your Auto Scaling group’s minimum size on demand and enhance your cloud management capabilities.