Amazon ElastiCache Cache Design - Choosing Between Redis and Memcached with Caching Strategies
Explore the criteria for choosing between Redis and Memcached, caching strategies like Lazy Loading and Write-Through, and how to leverage Serverless mode.
Criteria for Choosing Between Redis and Memcached
ElastiCache offers two engines, Redis and Memcached, delivering microsecond latency and handling millions of requests per second. Redis supports data persistence (AOF, RDB snapshots), read replicas, automatic failover, Pub/Sub messaging, and advanced data structures such as Sorted Sets and HyperLogLog. Beyond caching, Redis can serve as a session store, leaderboard, real-time ranking system, and message broker. Memcached features a multi-threaded architecture specialized for simple key-value caching. It is well-suited for scenarios where data persistence and replication are unnecessary and you simply want to cache database query results. For new projects, Redis is the predominant choice due to its rich feature set and operational flexibility.
Designing Caching Strategies
Lazy Loading (Cache-Aside) is a strategy that fetches data from the database on a cache miss and writes it to the cache. Since only actually requested data is stored in the cache, memory efficiency is high, but cache misses occur on first access. Write-Through is a strategy that updates the cache simultaneously with database writes. Cache data is always kept up to date, but write latency increases and data that is never read also gets cached. In practice, combining both approaches is effective: use Write-Through to update the cache on writes while setting TTL to automatically expire stale data. TTL values should be determined based on data freshness requirements - short (seconds to minutes) for data requiring real-time accuracy, and long (hours to days) for master data.
ElastiCache Serverless and Operations
ElastiCache Serverless, introduced in 2023, eliminates the need to pre-design node types or cluster sizes. Capacity automatically scales based on workload, starting from a minimal configuration and adapting to traffic increases. Pricing is based on pay-per-use for data storage and ElastiCache Processing Units (ECPU). It is particularly well-suited for new applications with unpredictable traffic patterns and development/test environments. On the other hand, for production environments with stable traffic patterns, provisioned configurations with reserved nodes may be more cost-effective. To gain a deeper understanding of ElastiCache, specialized books (Amazon) can be helpful.
ElastiCache Pricing
ElastiCache pricing is based on hourly node charges. A Redis cache.r7g.large costs approximately 0.252 USD per hour (about 181 USD per month). Serverless mode uses pay-per-use pricing for ECPU (ElastiCache Processing Units) at approximately 0.0034 USD per million ECPU, and storage at approximately 0.125 USD per GB per month. Serverless is more cost-effective for intermittent workloads, while provisioned nodes are more advantageous for consistently high-throughput workloads. Reserved nodes offer discounts of up to 55%.
Summary
ElastiCache is a caching service that directly reduces database load and improves application response times. Use Redis as the default choice and design your caching strategy with a combination of Lazy Loading and Write-Through. An effective approach is to start with Serverless mode for ease of use, then consider migrating to a provisioned configuration once your workload stabilizes.