This AWS Lambda function gets triggered on every auto scaling group CloudWatch Event being watched and creates/updates Route 53 Private Hosted Zone with A record set of all the Private IPs of the running instances in that auto scaling group.

In details:

• An Auto Scaling event triggered the Lambda function (Instance Launched / Instance Terminated)
• Checks if the Hosted Zone example.internal. exists for same VPC from which the auto scaling group event was triggered
• If Hosted Zone exists it obtains its ID
• Else (Hosted Zone doesn't exist) it creates the example.internal. Hosted Zone and obtains its ID
• Next it obtains a list of private IPs of all active instances in the auto scaling group which triggered this event
• If the list contains at least one instance it creates or updates a record set named <autoscaling_group_name>.example.internal. with the private IPs of the instances as A records
• Else the list is empty (which means the auto scaling group was deleted or doesn't contain any active instance) it deletes the record set named <autoscaling_group_name>.example.internal.
• example.internal. Hosted Zone can be renamed as desired by changing the variable domain in the py script

Files:

• aws_autoscaling_cloudwatch_event.json - CloudWatch Events to trigger the Lambda Function
• aws_autoscaling_execution_role.json - Permissions (Execution role) required for the lambda function to operate
• aws_autoscaling_lambda_function.py - Lambda function (written in Python 2.7)