A web design company currently runs several FTP servers for their 20 customers to upload and download large graphic files. They want to move this system to AWS. They also want to maintain customer privacy and keep the costs incurred on AWS side to a minimum.

Answer options:

A.Ask their customers to use an S3 client instead of an FTP client. Create a single S3 bucket. Create an IAM user for each customer. Put the IAM Users in a Group with an IAM policy that permits access to objects ( files ) within the bucket via the use of the ‘username’ policy variable.
B.Create a single S3 bucket with Reduced Redundancy Storage turned on and ask their customers to use an S3 client instead of an FTP client. Create a bucket for each customer with a Bucket Policy that permits access only to that one customer.
C.Create an Auto Scaling Group of FTP servers with a scaling policy to automatically scale-in when minimum network traffic on the auto-scaling group is below a given threshold. Load a central list of FTP users from S3 as part of the user data startup script on each Instance.
D.Create a single S3 bucket with Requester Pays turned on and ask their customers to use an S3 client instead of an FTP client. Create a bucket for each customer with a bucket policy that permits access only to that one customer.

Answer - A
The main considerations in this scenario are: (1) the architecture should be scalable, (2) customer privacy should be maintained, and (3) the solution should be cost-effective.
Option A is correct because (a) it creates permissions via IAM policy where each user will have access to only those objects ( files ) named with their username, and (b) S3 is a cost-effective and highly scalable solution.
Note: Even though creating one IAM User per user/customer is not the best way forwards, but given the other choices, this is the best option.
Option B is incorrect because creating one bucket per user is not a scalable architecture. One S3 bucket is enough for this scenario.
Option C is incorrect because creating an Auto Scaling group of FTP servers is a costly solution compared to creating buckets on S3 and appropriate IAM policies.
Option D is incorrect because (a) creating one bucket per user is not a scalable architecture. Currently, the number of customers is 20. But in the future, the number can grow. If it does, it will put limits on the number of buckets, and (b) you configure buckets to be Requester Pays when you want to share the data but not incur charges associated with others accessing the data. This will keep the cost down for the company but will increase the cost for the customer who will access the buckets.