Amazon ElastiCache Caching Strategy - Choosing Between Redis and Memcached
Compare Redis persistence and Pub/Sub capabilities with Memcached simplicity, and explore Valkey-compatible engine and Serverless mode options.
Choosing Between Redis and Memcached
Redis operates on a single-threaded event loop model and provides a rich set of data structures including strings, hashes, lists, sets, Sorted Sets, and Streams. It supports data persistence through AOF (Append Only File) and RDB snapshots, replication with automatic failover, and Pub/Sub messaging. Memcached features a multi-threaded architecture specialized for simple key-value caching. It offers easy horizontal scaling by adding nodes and is well-suited for pure caching use cases where data persistence and replication are not required.
Caching Patterns and Cluster Design
In the Lazy Loading (Cache-Aside) pattern, the application first checks the cache and, on a cache miss, retrieves data from the database and writes it to the cache. TTL is set to manage data freshness. In the Write-Through pattern, the cache is updated simultaneously with database writes, keeping cached data always current. Redis Cluster Mode uses hash slot-based sharding to distribute data, with up to 5 read replicas per shard. For node type selection, memory-optimized r-series instances are well-suited for caching workloads.
Valkey and Serverless
ElastiCache Serverless is a serverless option for Valkey (Redis-compatible) and Memcached that eliminates node management and scaling concerns. It uses pay-per-use pricing based on ECPU (ElastiCache Processing Units) and storage, automatically adapting to traffic fluctuations. Valkey is an open-source Redis-compatible engine and the new default engine for ElastiCache. It ensures high availability through automatic failover of read replicas and multi-AZ deployment. Global Datastore enables cross-region replication for disaster recovery and improved global read latency. For a systematic understanding of caching from basics to advanced topics, books (Amazon) provide comprehensive coverage.
ElastiCache Pricing
ElastiCache node-based pricing for a cache.r7g.large is approximately 0.252 USD per hour (about 181 USD per month). Serverless uses pay-per-use pricing for ECPU (approximately 0.0034 USD per million ECPU) and storage (approximately 0.125 USD per GB per month). Node-based pricing is more economical for stable traffic, while Serverless is better suited for variable traffic. Reserved nodes offer discounts of up to 55%. Monitor cache hit rates with CloudWatch and regularly right-size your nodes.
Summary
ElastiCache offers two engines, Redis and Memcached, to be selected based on workload requirements. The key design considerations are choosing the appropriate caching pattern between Lazy Loading and Write-Through, and ensuring scalability through Cluster Mode sharding and read replicas.