Connection Rejection Cascade From Maxclient Saturation
criticalWhen Redis reaches maximum client connections (redis.connections.rejected increasing), new connection attempts fail silently while existing connections continue working normally, creating intermittent failures that are difficult to diagnose from application metrics alone.
Monitor redis.connections.rejected counter incrementing while redis.clients.connected approaches or equals maxclients configuration limit. Application-level connection errors may spike while Redis CPU and memory appear healthy. Often correlates with sudden traffic bursts or connection pool leaks.
Immediately increase maxclients configuration in Redis. Investigate application connection pool settings - ensure proper connection reuse and pool size limits. Check for connection leaks in application code (connections opened but not closed). Consider implementing connection pooling at infrastructure level (Envoy, HAProxy). Monitor redis.connections.received rate to understand connection churn.