Amazon ElastiCache provides in-memory caching which improves performance for read requests when
the data is cached in ElastiCache. ElastiCache can be placed in front of your database.
Amazon RDS is a relational SQL type of database. It is not a service that you place in front of
another database to improve performance. Instead you might use RDS as your back-end database and
use ElastiCache in front of it to improve performance through its in-memory caching.
Amazon EFS is an Elastic File System, not a caching service.
Amazon RedShift is a data warehouse that is used for performing analytics on data.