https://www.udemy.com/aws-certified-solutions-architect-associate/learn/v4/t/lecture/2152298?start=0

ElastiCache is  a web service that makes it easy to deploy, operate and scale an in-memory cache in the cloud.  The service improves the performance of web applications by allowing you to retrieve information from fast, managed, in-memory caches, instead of relying entirely on slower disk-based databases.

ElastiCache can be used to significantly improve latency and throughput for many read-heavy application workloads (such as social networking, gaming, media sharing and Q&A portals) or compute-intensive workloads (such as a recommendation engine).

Caching improves application performance by storing critical pieces of data in memory for low-latency access.  Cached information may include the results of I/O-intensive database queries or the results of computationally-intensive calculations.

Types of ElastiCache

• Memcached
  • Widely adopted memory object caching system.  ElastiCache is protocol compliant with Memcahced, so popular tools that you use today with existing Memcached environments will work seamlessly with the service.
• Redis
  • Popular open-sourced in-memory key-value store that supports data structures such as sorted sets and lists.  ElastiCache supports Master / Slave replication and Multi-AZ which can be used to achieve cross AZ redundancy.

Exam Tips

• Typically you will be given a scenario where a particular database is under a lot of stress/load.  You may be asked which service you should use to alleviate this.
  • ElastiCahce is a good choice if your database is particularly read heavy and not prone to frequent changing.
  • RedShift is a good answer if the reason your database is failing is because management keep running OLAP transactions on it.