Your company has a 3 tier application that consists of a Web, Application and Database Tier. The application is based on delivering RESTful services. They have Autoscaling Groups for the EC2 Instances for the Web and Application Tier. You now want to add high availability to the Tiers. But it needs to ensure that each tier can be scaled independently. How would you architect? Choose the most PREFERRED option, assuming that the application tier is HTTPS throughout.

Answer options:

A.Create an Application Load Balancer and add separate target groups for the Web and Application Tier.
B.Create an Application Load Balancer for the Application Tier and a classic load balancer for the Web Tier.
C.Create a Classic Load Balancer and add multiple targets for the Web and Application Tier.
D.Create separate Classic Load Balancers for the Web and Application Tiers.

Answer – A
An Application Load Balancer functions at the application layer, the seventh layer of the Open Systems Interconnection (OSI) model. After the load balancer receives a request, it evaluates the listener rules in priority order to determine which rule to apply and then selects a target from the target group for the rule action. You can configure listener rules to route requests to different target groups based on the content of the application traffic. 
Application Load Balancer supports a round-robin load-balancing algorithm. Additionally, Application Load Balancer supports a slow start mode with the round-robin algorithm that allows you to add new targets without overwhelming them with a flood of requests. With the slow start mode, targets warm-up before accepting their fair share of requests based on a ramp-up period that you specify. Slow start is very useful for applications that depend on cache and need a warm-up period before responding to requests with optimal performance.
It does support HTTP/HTTPS protocols. Compared to Classic Load Balancers, an Application Load Balancer provides more features such as host-based routing, slow start, etc., which is ideal for web and application traffic load balancing. 
The AWS Documentation also mentions independent working of target groups under the Application Load Balancer.
Support for monitoring the health of each service independently, as health checks are defined at the target group level, and many CloudWatch metrics are reported at the target group level. Attaching a target group to an Auto Scaling group enables you to scale each service dynamically based on demand.
For more information on the Application Load Balancer, please refer to the below URL
https://docs.aws.amazon.com/elasticloadbalancing/latest/application/introduction.html