Your company hosts a social media site supporting users in multiple countries.
You have been asked to provide a highly available design for the application that leverages
multiple regions for the most recently accessed content and latency sensitive portions of the web
site. The most latency sensitive component of the application Involves reading user preferences
to support web site personalization and ad selection.
In addition to running your application in multiple regions, which option will support this
application’s requirements?

A.
Use the S3 Copy API to copy recently accessed content to multiple regions and serve user
content from S3, CloudFront with dynamic content, and an ELB in each region.
Retrieve user preferences from an ElastiCache cluster in each region and leverage SNS
notifications to propagate user preference changes to a worker node in each region.

B.
Serve user content from S3, CloudFront with dynamic content, and an ELB in each region.
Retrieve user preferences from an ElastiCache cluster in each region and leverage Simple
Workflow (SWF) to manage the propagation of user preferences from a centralized DB to each
ElastiCache cluster.

C.
Serve user content from S3, CloudFront, and use Route53 latency-based routing between ELBs
in each region.
Retrieve user preferences from a local DynamoDB table in each region and leverage SQS to
capture changes to user preferences with SQS workers for propagating updates to each table.

D.
Use the S3 Copy API to copy recently accessed content to multiple regions and serve user
content from S3, CloudFront, and Route53 latency-based routing between ELBs in each region.
Retrieve user preferences from a DynamoDB table and leverage SQS to capture changes to user
preferences with SQS workers for propagating DynamoDB updates.

Explanation:
http://media.amazonwebservices.com/architecturecenter/AWS_ac_ra_mediasharing_09.pdf
http://media.amazonwebservices.com/architecturecenter/AWS_ac_ra_adserving_06.pdf