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.
2. Write Throgh: When data is written to the the db, also write to cache
3. 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: