Your company currently has a set of EC2 Instances running a web application which sits behind an Elastic Load Balancer. You also have an Amazon RDS instance which is used by the web application. You have been asked to ensure that this architecture is self healing in nature and cost effective. Which of the following would fulfill this requirement. Choose 2 answers from the option given below

Answer options:

A.Use Cloudwatch metrics to check the utilization of the web layer. Use Autoscaling Group to scale the web instances accordingly based on the cloudwatch metrics.
B.Use Cloudwatch metrics to check the utilization of the database servers. Use Autoscaling Group to scale the database instances accordingly based on the cloudwatch metrics.
C.Utilize the Read Replica feature for the Amazon RDS layer
D.Utilize the Multi-AZ feature for the Amazon RDS layer

Answer - A and D
The following diagram from AWS showcases a self-healing architecture where you have a set of EC2 servers as Web server being launched by an Autoscaling Group.
The AWS Documentation mentions the following
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. Since the endpoint for your DB Instance remains the same after a failover, your application can resume database operation without the need for manual administrative intervention.
For more information on Multi-AZ RDS, please refer to the below link:
https://aws.amazon.com/rds/details/multi-az/