How should a developer modify the application to improve performance?

Explanations:

Using Amazon ElastiCache to cache query results reduces the load on the RDS instance by serving frequent read requests from the cache. This can significantly improve performance during peak times, as it minimizes latency and helps to avoid hitting the database for every read operation.

Scaling the ECS cluster to contain more ECS instances may help distribute the workload across more application servers but does not directly address the underlying database performance issues. If the database is the bottleneck due to high read latency, simply increasing ECS instances won’t resolve the database’s read performance problems.

Adding read capacity units (RCUs) is applicable to Amazon DynamoDB, not Amazon RDS for MySQL. RDS does not use a capacity model like DynamoDB; instead, it requires scaling vertically (upgrading instance types) or horizontally (read replicas) to improve read performance. Therefore, this option is not relevant in this context.

Modifying the ECS task definition to increase the task memory may improve the performance of the application itself but does not directly affect the performance of the RDS database. If the database is underperforming due to high read latency, simply increasing the task memory of ECS tasks will not resolve the core issue of database read performance.