Refer to the architecture diagram above of a batch processing solution using Simple Queue
Service (SQS) to set up a message queue between EC2 instances which are used as batch
processors. CloudWatch monitors the number of job requests (queued messages) and an Auto
Scaling group adds or deletes batch servers automatically based on parameters set in
CloudWatch alarms.
You can use this architecture to implement which of the following features in a cost effective and
efficient manner?

A.
Coordinate number of EC2 instances with number of Job requests automatically, thus improving
cost effectiveness.

B.
Reduce the overall time for executing Jobs through parallel processing by allowing a busy EC2
instance that receives a message to pass it to the next instance in a daisy-chain setup.

C.
Implement fault tolerance against EC2 instance failure since messages would remain in SQS and
work can continue with recovery of EC2 instances.
Implement fault tolerance against SQS failure by backing up messages to S3.

D.
Handle high priority Jobs before lower priority Jobs by assigning a priority metadata field to SQS
messages.

E.
Implement message passing between EC2 instances within a batch by exchanging messages
through SQS.

Explanation:
https://docs.aws.amazon.com/AutoScaling/latest/DeveloperGuide/as-using-sqs-queue.html