A read-only news reporting site has a web application tier in EC2 and a database tier in RDS. The website receives large and unpredictable read traffic and automatically responds to these traffic fluctuations. Which of the following AWS services are the most suitable to meet the requirements?

Answer options:

A.Stateless instances for the web application tier in an auto-scaling group monitored with CloudWatch. RDS configured with read replicas. Add Amazon ElastiCache for RDS.
B.Stateful instances for the web application tier in an auto-scaling group monitored with CloudWatch. RDS with read replicas.
C.Stateful instances for the web application tier in an auto-scaling group monitored with CloudWatch. RDS with Multi-AZ.
D.Stateless instances for the web application tier in an auto-scaling group monitored with CloudWatch. RDS with Multi-AZ.

Answer – A
The scenario asks for 2 things: (1) a performance improvement solution for read-heavy web tier and database tier. Hint: Always see if any of the options contain caching solutions such as ElastiCache, CloudFront, or Read Replicas, and (2) whether to use stateless or stateful instances.
Stateful instances are not suitable for distributed systems, as they retain the state of connection between client and web server. And the database remains engaged as long as the session is active. Hence, it increases the load on the server as well as the database. Stateless instances, however, are distributed and easy to scale in/scale-out. Hence, the stateless application tends to improve the performance of a distributed application.
Option A is CORRECT because (a) it uses stateless instances, (b) the webserver uses ElastiCache for read operations, (c) it uses CloudWatch which monitors the fluctuations in the traffic and notifies to the auto-scaling group to scale in/scale-out accordingly, and (d) it uses read replicas for RDS to handle the read-heavy workload.
Option B is incorrect because (a) it uses stateful instances, and (b) it does not use any caching mechanism for web and application tier.
Option C is incorrect because (a) it uses stateful instances, (b) it does not use any caching mechanism for web and application tier, and (c) multi-AZ RDS does not improve read performance.
Option D is incorrect because multi-AZ RDS does not improve read performance.
For more information on ElastiCache and Read Replicas, please refer to the following links-
https://aws.amazon.com/elasticache/
https://aws.amazon.com/rds/details/read-replicas/