A company has a multi-tier application that runs six front-end web servers in an Amazon EC2 Auto Scaling group in a single Availability Zone behind an Application Load Balancer (ALB) A solutions architect needs to modify the infrastructure to be highly available without modifying the application
Which architecture should the solutions architect choose that provides high availability?
A . Create an Auto Scaling group that uses three instances across each of two Regions
B . Modify the Auto Scaling group to use three instances across each of two Availability Zones
C . Create an Auto Scaling template that can be used to quickly create more instances in another Region
D . Change the ALB in front of the Amazon EC2 instances in a round-robin configuration to balance traffic to the web tier
Answer: B
Explanation:
https://docs.aws.amazon.com/autoscaling/ec2/userguide/as-add-availability-zone.html
Expanding Your Scaled and Load-Balanced Application to an Additional Availability Zone
When one Availability Zone becomes unhealthy or unavailable, Amazon EC2 Auto Scaling launches new instances in an unaffected zone. When the unhealthy Availability Zone returns to a healthy state, Amazon EC2 Auto Scaling automatically redistributes the application instances evenly across all of the zones for your Auto Scaling group. Amazon EC2 Auto Scaling does this by attempting to launch new instances in the Availability Zone with the fewest instances. If the attempt fails, however, Amazon EC2 Auto Scaling attempts to launch in other Availability Zones until it succeeds.
You can expand the availability of your scaled and load-balanced application by adding an Availability Zone to your Auto Scaling group and then enabling that zone for your load balancer. After you’ve enabled the new Availability Zone, the load balancer begins to route traffic equally among all the enabled zones.
https://docs.aws.amazon.com/autoscaling/ec2/userguide/as-add-availability-zone.html