Redis Connection Errors — Server Connection Refused and Memory Limit Issues

Overview

Fix Redis connection errors including ECONNREFUSED, OOM command not allowed, max clients reached, and authentication failures on Linux.

Key Details

• Redis defaults to local-only connections on port 6379 with no authentication
• OOM (Out of Memory) errors occur when Redis reaches maxmemory limit
• Redis can be configured for persistence (RDB snapshots, AOF log) or as a pure cache
• Connection limits (maxclients, default 10000) can be exhausted by applications not closing connections
• Redis Sentinel and Cluster add complexity to connection handling

Common Causes

• Redis server not running or listening on a different port/address than expected
• maxmemory limit reached with no eviction policy — Redis rejects write commands
• All client connections used up (maxclients reached)
• Authentication required but client not providing the password (requirepass set)

Steps

1. 1Check Redis status: 'systemctl status redis' and 'redis-cli ping' (should return PONG)
2. 2For OOM: set eviction policy in redis.conf: 'maxmemory-policy allkeys-lru' to evict least-recently-used keys
3. 3Check connections: 'redis-cli info clients' shows connected clients and blocked clients
4. 4Configure authentication: set 'requirepass yourpassword' in redis.conf, connect with 'redis-cli -a yourpassword'
5. 5Monitor in real-time: 'redis-cli monitor' shows all commands being processed (warning: high overhead in production)

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