Backend & systems·Concurrency and coordination
you need only one instance across the whole fleet to run the job, so they all try to claim a key in Redis first.
Distributed lock
Mutual exclusion coordinated through an external store shared by multiple processes. It is far weaker than an in-process lock: the holder can be paused, partitioned or garbage-collected while its lease expires, and it will not know. Safe use needs a lease plus a fencing token checked by the resource itself.