ElastiCache Architecture

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Useful Links:
Exam Tips:
- Supports any RDS DB or even no DB at all is required.
- Be aware of scenarios where it is need:
  - Used to improve database performance by caching query results.
  - Used where read heavy workloads with low latency requirements.
  - Reduces database workloads, meaning savings.
  - Application needs to know to use caching. - Application changes.
- Understand the differences between Redis and Memcached:
  - Advanced data structures beyond key value stores, you have to use Redis.
  - Vertical scaling = Memcached
  - High Availability = Redis
  - Data Durability:
    - Redis data is not persistent by default, but you can enable the Append-Only File (AOF). This allows the Redis node to write all of the commands that modify the cache data to an append-only file.
    - In the case a Redis node is rebooted, the AOF allows the Redis node to have a warm cache with the data intact.
    - Disabled by default, enabled by assigning a parameter group with appendonly set to yes.
    - You can use appendfsync to determine how often the AOF file is written to.

Memcached	Redis
Simple Data Structures	Advanced Structures
No replication	Multi-AZ
Multiple nodes (Sharding)	Replication (Scaled Reads)
No backups	Backup & restore
Multi-threaded	Transactions