Interview › Databases & Caching
What is ElastiCache, and what does it manage?
Databases & Caching · Intermediate level
Answer
ElastiCache is AWS managed in-memory caching for Valkey, Redis OSS, and Memcached. AWS manages nodes, patching, monitoring integration, replication/failover features, and backups where supported; I own keys, TTLs, consistency, and fallback behavior.
Technical explanation
Managed cache still requires correct key design, TTLs, invalidation, memory sizing, security, and fallback behavior.
Redis/Valkey is better for counters, rate limits, sorted sets, locks, streams, and HA patterns; Memcached is good for simple ephemeral object cache.
The cache should not become a hidden source of truth unless durability, backup, and failover are deliberately designed.
Hands-on example
Cache-aside example:
GET product:v1:123
If hit, return cached value.
If miss, query RDS, then SETEX product:v1:123 300 <json>.
Redis data type examples:
INCR api:tenant:42:requests
HSET user:123 tier premium
ZADD leaderboard 9100 user:123
XADD orders:events * order_id 1001 status created
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