You have been hired as an AWS Architect for a company. There is a requirement to host an application using EC2 Instances. The Infrastructure needs to scale on-demand and also be fault-tolerant. Which of the following would you include in the design? (Select TWO)

Answer options:

A.AWS Auto Scaling
B.Amazon GuardDuty
C.Elastic Load Balancing
D.Amazon CloudWatch

Correct Answers: A and C
The AWS Documentation mentions the following
You can automatically increase the size of your Auto Scaling group when demand goes up and decrease it when demand goes down. As the Auto Scaling group adds and removes EC2 instances, you must ensure that the traffic for your application is distributed across all of your EC2 instances. The Elastic Load Balancing service automatically routes incoming web traffic across such a dynamically changing number of EC2 instances. 
Option B is incorrect since Amazon GuardDuty is a threat detection service that continuously monitors for malicious activity and unauthorized behaviour.
Option D is incorrect since CloudWatch is a monitoring service
For more information on AWS Autoscaling and ELB, please visit the below URL
https://docs.aws.amazon.com/autoscaling/ec2/userguide/autoscaling-load-balancer.html
https://aws.amazon.com/guardduty/