Amazon ElastiCache CloudWatch AlarmsThresholds, failures, and debugging guides

CPUUtilization measures the percentage of CPU used by the entire cache node host, across all vCPUs — including the engine process plus OS and background management processes.

Evictions counts the number of keys removed from the cache because the node hit its maxmemory limit — the engine had to make room for new writes by forcibly discarding existing data (distinct from keys expiring naturally via TTL).

CurrConnections reports the number of client connections open to the node at the moment it's sampled. For Redis/Valkey it excludes read-replica connections and a handful (4–6) of connections ElastiCache itself uses to monitor the cluster; for Memcached the reserved/internal count differs slightly.

DatabaseMemoryUsagePercentage reports the percentage of the engine's configured maxmemory currently in use, calculated as used_memory ÷ maxmemory from the Redis/Valkey INFO command. It is Redis/Valkey-specific — Memcached clusters do not emit this metric.