Amazon ElastiCache

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 is a good choice if your database is particularly read heavy and not prone to frequent changing. ElastiCache can also be used on top of compute resources.

Caching Engines

ElastiCache supports two open-source in-memory caching engines: Memcached and Redis.


Memcached is a widely adopted memory object caching system. ElastiCache is protocol compliant with Memcached, so popular tools that you use today with existing Memcached environments will work seamlessly with the service.

Memcached is good for simple caching use. It's a good choice for object caching. ElastiCache manages Memcached nodes as a pool that can grow and shrink. Thus Memcached has multithreaded performance and scales horizontally.


Redis is a popular open-source 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.

Redis is better for advanced use than Memcached. Redis provides more advanced data types than Memcached (like lists, hashes, and sets). Redis also provides in-memory sorting and ranking for datasets. Really useful if your application provides a leaderboard. Redis is also more durable than Memcached with persistence and failover.

Caching Strategies

ElastiCache supports lazy loading and write-through.

Lazy Loading Strategy

Lazy loading loads the data into the cache only when necessary. If requested data isn't in the cache, ElastiCache returns null and fetches the data. This means that only requested data is ever cached. Note that there's a cache miss penalty.

A TTL specified the number of seconds until the key expires to avoid keeping stale data in the cache. Lazy loading treats an expired key as a cache miss.

Write Through Strategy

Write through adds or updates data to the cache whenever data is written to the database. This means that writes now have a penalty. But it does mean that data in the cache is never stale.