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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
    • Leaderboards (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