Redis connection exhaustion — pool management and proper cleanup

Redis server stops accepting connections with max number of clients reached. Application gets ECONNREFUSED or timeout errors. Common in serverless and horizontally scaled environments.

Fixes: (1) Use connection pooling — ioredis has built-in pooling. (2) Always close connections in finally blocks. (3) In serverless: reuse connections across invocations by declaring client outside handler, or use Upstash REST-based Redis. (4) Set maxclients in redis.conf higher and monitor with INFO clients. (5) Set idle timeout: CONFIG SET timeout 300. (6) Check for leaks: CLIENT LIST to see all connections.

Each Redis connection consumes a file descriptor and memory. Without pooling, each request creates a new connection. Serverless functions are especially prone because each cold start creates a new connection.