Database
Amazon ElastiCache
Managed in-memory caching
Amazon ElastiCache provides managed Redis OSS and Memcached in-memory data stores. Used for sub-millisecond caching, session stores, leaderboards, and offloading repeated database reads via cache-aside patterns.
When to use it
- Caching repeated database query results
- Session state shared across a web fleet
- Real-time leaderboards, counters, pub/sub (Redis)
- Reducing load on RDS/DynamoDB for hot reads
When NOT to use it
- Durable primary storage — ElastiCache is a cache, not a system of record
- Data that must survive node failure without a backing store
Key exam points
- Redis OSS supports persistence, replication, and pub/sub; Memcached is simpler and multi-threaded
- Cache-aside (lazy loading) vs write-through patterns
- Multi-AZ replication for cache availability
- For DynamoDB specifically, DAX is the purpose-built in-memory accelerator
Compared with
- Amazon DynamoDB — DynamoDB + DAX is AWS's managed accelerator path for NoSQL; ElastiCache is the general-purpose cache.
- Amazon RDS — ElastiCache typically sits in front of RDS to absorb repeated reads.