When would you use a Redis distributed lock, and what can go wrong?

Use Redis locks only with clear lease boundaries

Explains the risks of Redis-based distributed locks and when database constraints, queues, or idempotency are safer.

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I would use a Redis lock only for a short, bounded coordination problem where duplicate work is undesirable but the system can tolerate lease expiry behavior. The lock needs an expiration so it does not stay forever if the holder crashes. The worker also needs to know that the lock can expire before work finishes, so the protected operation should still be idempotent or guarded by a stronger source-of-truth rule.

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Distributed coordination, lock expiry, leases, ownership tokens, idempotency, database constraints, and failure modes.

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A Redis lock is a time-bounded lease, not a durable mutex. Expiry, pauses, partitions, failover, and ownership races mean correctness still needs an idempotent operation, database constraint, or another durable boundary.
I would use a Redis lock only for a short, bounded coordination problem where duplicate work is undesirable but the system can tolerate lease expiry behavior. The lock needs an expiration so it does not stay forever if the holder crashes. The worker also needs to know that the lock can expire before work finishes, so the protected operation should still be idempotent or guarded by a stronger source-of-truth rule.
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For many correctness problems, I would prefer database uniqueness, optimistic concurrency, transactions, queues, or idempotency keys over a distributed lock. A Redis lock can help reduce duplicate refreshes or schedule one background task, but it should not be the only protection for money movement, inventory reservation, or authorization. If I use one, I would include an ownership token and release only the lock I acquired.

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Using Redis locks as the only correctness mechanism for critical data.
Creating locks without expiry.
Releasing a lock without verifying ownership.
Running long work under a short lease without idempotency.

When would you use a Redis distributed lock, and what can go wrong?

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