As a solution architect professional, you have been requested to launch 20 Large EC2 instances which will all be used to process huge amounts of data. There is also a requirement that these instances need to transfer data back and forth among each other and need a low-latency network performance. Which of the following would be the most efficient setup to achieve this?

Answer options:

A.Ensure that all the instances are placed in the same region.
B.Ensure that all instances are placed in the same Availability Zone.
C.Use a cluster Placement Group and ensure that all instances are launched in it.
D.Use the largest EC2 instances currently available on AWS and make sure they are spread across multiple Availability Zones.

Answer – C
Option A is incorrect because being in the same region would not mean that the data transfer between the instances would be faster. In fact, the instances would experience network latency.
Option B is incorrect because just being in the same AZ is not sufficient. They should be added to a Placement Group to benefit from the low network latency.
Option C is CORRECT because Placement Group enables applications to get the low-latency network performance necessary for tightly-coupled node-to-node communication typical of many high-performance computing applications. 
Option D is incorrect because despite being of the largest size, the EC2 instances would still experience network latency if they are not part of a Placement Group.
More information on Placement Groups:
A placement group is a logical grouping of instances within a single Availability Zone. Placement groups are recommended for applications that benefit from low network latency, high network throughput, or both. To provide the lowest latency, and the highest packet-per-second network performance for your placement group, choose an instance type that supports enhanced networking.
For more information on Placement Groups, please visit the URL
http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/placement-groups.html