ElastiCache

Overview: The same way RDS is to get managed Relational Databases, ElastiCache is to get managed Redis or Memcached. Caches are in-memory databases with really high performance, low latency. They help reduce loads off of databases for read intensive workloads. They help make your application stateless.

• Write scaling using shading.
• Read scaling using Read Replicas
• Multi AZ with Failover Capability
• AWS takes care of OS maintenance / patching, optimizations, setup, configuration, monitoring, failure recovery and backups

Solution Architecture - DB Cache

• Applications queries ElastiCache, if not available, get from RDS and store in ElastiCache
• Helps relieve load in RDS
• Cache must have an invalidation strategy to make sure only the most current data is used in there User Session Store
• User logs into any of the applications
• The application writes the session data into ElastiCache
• The user hits another instance of our application
• The instance retrieves the data and the user is already logged in

Redis Overview

• Redis is an in-memory key-value store
• Super low latency (sub ms)
• Cache survive reboots by default (it’s called persistence)
• Great to host
  • User sessions
  • Leader boards (for gaming)
  • Distributed states
  • Relieve pressure on databases (such as RDS)
  • Pub / Sub capability for messaging
• Multi AZ with Automatic failover for Disaster Recovery if you don’t want to lose your cache data
• Support for Read Replicas

Memcached Overview

• Memcached is an in-memory object store
• Cache doesn’t survive reboots
• Use cases:
• Quick retrieval of objects from memory
• Cache often accessed objects
• Overall, Redis has largely grown in popularity and has better feature sets than memcached
• Most likely, you’d probably only want to use Redis for caching needs