You have an application consisting of a stateless web server tier running on Amazon EC2 instances behind a load balancer and using Amazon RDS with read replicas. Which of the following methods should you use to implement a self-healing architecture? Choose 2 answers from the options given below. 

Answer options:

A.Set up an Auto Scaling group for the webserver tier along with an Auto Scaling policy that uses the Amazon RDS DB CPU utilization CloudWatch metric to scale the instances.
B.Set up an Auto Scaling group for the webserver tier along with an Auto Scaling policy that uses the Amazon EC2 CPU utilization CloudWatch metric to scale the instances.
C.Use a larger Amazon EC2 instance type for the webserver tier and a larger DB instance type for the data storage layer to ensure that they don’t become unhealthy.
D.Set up an Auto Scaling group for the database tier along with an Auto Scaling policy that uses the Amazon RDS read replica lag CloudWatch metric to scale out the Amazon RDS read replicas.
E.Use an Amazon RDS Multi-AZ deployment.

Answer – B and E
The scaling of EC2 Instances in the Autoscaling group is normally done with the metric of the CPU utilization of the current instances in the Autoscaling group.
For more information on scaling in your Autoscaling Group, please refer to the below link:
http://docs.aws.amazon.com/autoscaling/latest/userguide/as-scaling-simple-step.html
Amazon RDS Multi-AZ deployments provide enhanced availability and durability for Database (DB) Instances, making them a natural fit for production database workloads. When you provision a Multi-AZ DB Instance, Amazon RDS automatically creates a primary DB Instance and synchronously replicates the data to a standby instance in a different Availability Zone (AZ). Each AZ runs on its own physically distinct, independent infrastructure and is engineered to be highly reliable. In case of an infrastructure failure, Amazon RDS performs an automatic failover to the standby (or to a read replica in the case of Amazon Aurora), so that you can resume database operations as soon as the failover is complete. 
For more information on RDS Multi-AZ, please refer to the below link:
https://aws.amazon.com/rds/details/multi-az/
Option A is incorrect because the database CPU usage should not be used to scale the web tier.
Option C is incorrect because increasing the instance size does not always guarantee that the solution will not become unhealthy.
Option D is incorrect because increasing Read-Replica’s will not suffice for write operations if the primary DB fails.