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# ElastiCache
## Overview
ElastiCache is Amazon's offering for managed Redis or Memcached.
Caches are in-memory dbs with high perf and low latency. They allow quick access to data without having to reach the DB disk.
This helps:
- Latency
- Reduce load on DB resources
- Makes application stateless
> AWS will take care of maintenance, patching, optimisations, monitoring, failure etc for you
## Architecture
Apps query the cache, but if it misses, then it will read from DB.
Caches should have an invalidation strategy
## Use session store
Another good use case is for a session store for a user's session:
## Elasticcache security
- ElastiCache support IAM Auth for Redis
- IAM is only used for API level access, though
- There is also Redis auth, which allows you to create a user/pw combination for Redis cluster and is an extra layer of security
- Memcached supports SASL based auth
## ElastiCache patterns
1. **LazyLoading**: this involves writing all data to cache for quick access. Data can quickly become stale.
1. **Write Throgh**: When data is written to the the db, also write to cache
1. **Session store**: Store temporary data in cache (such as session info)
## Redis use case
> Important for the exam
- Gaming leaderboards are computationally complex
- **Redis sorted sets** guarantees uniqueness and element ordering
- Each time an element is added, it's ranked in realtime, then added in correct order:
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