You have deployed an application in an Auto Scaling Group. You now want to change the instance type of the instances as the new instance type can improve the application performance. During the change, there should be no service impact. How can you achieve this requirement in the most appropriate way?

Answer options:

A.Switch to Elastic Beanstalk to deploy the application with the new instance type.
B.Delete the old Auto Scaling group and use Cloudformation to deploy the new Auto Scaling group with the new instance type.
C.Create a new launch configuration with the new instance type, attach it to the existing autoscaling group and increase the number of desired instances of ASG to launch new instances. When new instances are in healthy status, decrease the number of desired instances to delete instances with the old instance type.
D.Create new EC2 instances with the new instance type and attach them to the Auto Scaling Group.

Answer - C
The ideal way is to create a new launch configuration, attach it to the existing Auto Scaling group, and replace the existing instances with the new ones.
Option A is invalid because it is not needed to switch to Elastic Beanstalk. You should directly change the configurations of the ASG.Option B is invalid because by deleting the old ASG, there will be a service impact.
Option D is invalid because you need to modify the launch configuration of the Auto Scaling group. Otherwise, new instances of the ASG will still use the old instance type.
For more information on the launch configuration of Auto Scaling groups, please refer to the below document link:
http://docs.aws.amazon.com/autoscaling/latest/userguide/LaunchConfiguration.html