Question 1

How do I set up ShedLock with Spring Boot and Redis?

Accepted Answer

Add the shedlock-spring and shedlock-provider-redis-spring dependencies, configure a RedisLockProvider bean with your RedisConnectionFactory, and annotate scheduled methods with @SchedulerLock. The README provides code snippets for exact configuration steps.

Question 2

ShedLock vs db-scheduler: which is better for job scheduling?

Accepted Answer

ShedLock is best for simple at-most-once execution in existing scheduled tasks, while db-scheduler is a full distributed scheduler with job persistence, retries, and dependencies. Choose ShedLock if you only need locking; otherwise, opt for a scheduler like db-scheduler or JobRunr.

Question 3

What happens if a task runs longer than lockAtMostFor in ShedLock?

Accepted Answer

The lock expires, and another instance might acquire it, leading to duplicate execution. The README warns to set lockAtMostFor significantly longer than the maximum execution time and treats it as a safety net for node failures.

Question 4

Can ShedLock handle clock skew in Kubernetes clusters?

Accepted Answer

Yes, but you must mitigate it by using lock providers with database time (e.g., JdbcTemplate with usingDbTime()) to rely on the DB server's clock, and set lockAtLeastFor to account for minor differences, as recommended in the README.

Question 5

Is ShedLock suitable for very short-running tasks?

Accepted Answer

Yes, but use lockAtLeastFor to prevent rapid successive executions due to clock differences or short durations. The README's troubleshooting section suggests this for tasks that finish quickly.

Question 6

How do I test ShedLock without an external database?

Accepted Answer

Use the InMemoryLockProvider in tests by adding shedlock-provider-inmemory as a test dependency and configuring it as a bean. The README shows an example with scope set to test for isolation.

Question 7

Does ShedLock support reactive programming with Spring WebFlux?

Accepted Answer

Yes, via reactive lock providers like ReactiveRedisLockProvider or R2DBC, but the README notes that R2DBC support is experimental and limited, so use with caution in production.

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