You currently have EC2 Instances hosting an application. These instances are part of an Autoscaling Group created using Cloudformation. You now want to change the instance type of the EC2 Instances. How can you manage the deployment with the least amount of downtime?

Answer options:

A.Terminate the existing Auto Scaling group. Create a new launch configuration with the new Instance type. Attach that to the new Auto-scaling Group.
B.Use the AutoScalingRollingUpdate policy on CloudFormation Template Auto Scaling group
C.Use the Rolling Update feature which is available for EC2 Instances.
D.Manually terminate the instances, launch new instances with the new instance type and attach them to the Autoscaling group.

Answer - B
The AWS::AutoScaling::AutoScalingGroup resource supports an UpdatePolicy attribute. This is used to define how an Auto Scaling group resource is updated when an update to the CloudFormation stack occurs. A common approach to updating an Auto Scaling group is to perform a rolling update, which is done by specifying the AutoScalingRollingUpdate policy. This retains the same Auto Scaling group and replaces old instances with new ones, according to the parameters specified.
For more information on AutoScaling Rolling Update, please refer to the below link:
https://aws.amazon.com/premiumsupport/knowledge-center/auto-scaling-group-rolling-updates/