You currently have an Auto Scaling group with an Elastic Load Balancer and need to phase out all instances and replace them with a new instance type. What are 2 ways by which this can be achieved?

Answer options:

A.Use NewestInstance to phase out all instances that use the previous configuration.
B.Attach an additional ELB to your Auto Scaling configuration and phase in newer instances while removing older instances.
C.Use OldestLaunchConfiguration to phase out all instances that use the previous configuration.
D.Attach an additional Auto Scaling configuration behind the ELB and phase in newer instances while removing older instances.

Answer - C and D
When using theOldestLaunchConfiguration policy, Auto Scaling terminates instances that have the oldest launch configuration. This policy is useful when you`re updating a group and phasing out the instances from a previous configuration.
For more information on Autoscaling instance termination, please visit the below URL:
http://docs.aws.amazon.com/autoscaling/latest/userguide/as-instance-termination.html
Option D is an example of Blue Green Deployments.
A blue group carries the production load while a green group is staged and deployed with the new code. When it’s time to deploy, you simply attach the green group to the existing load balancer to introduce traffic to the new environment. For HTTP/HTTPS listeners, the load balancer favors the green Auto Scaling group because it uses the least outstanding requests routing algorithm.
As you scale up the green Auto Scaling group, you can take blue Auto Scaling group instances out of service by either terminating them or putting them in Standby state,
For more information on Blue Green Deployments, please refer to the below document link: from AWS
https://d0.awsstatic.com/whitepapers/AWS_Blue_Green_Deployments.pdf