How Redis Distributed Locking Prevents Duplicate Scheduled Jobs Across Servers

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When a team scaled their product-import service from one server to ten, all instances began firing the same hourly job simultaneously, causing redundant API calls, extra costs, and potential database duplicates. To fix this, they implemented distributed locking using Redis, where every server races to acquire a lock before executing the job, and only the winner proceeds while others skip that run. The lock is set atomically using Redis's SET NX EX command, ensuring no two servers can claim it at the same time and that it auto-expires if the winning server crashes. Each lock is tagged with a unique random token, and release is handled via a Lua script to ensure the check-and-delete operation is atomic, preventing a server from accidentally releasing another server's lock. The solution requires no dedicated leader election or manual failover logic, relying entirely on a Redis instance most teams already operate.

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