ShedLock: Running multiple instances runs scheduler tasks multiple times

Question

I am using Shedlock to run my scheduler task only once if multiple instances of the service are running.

I followed the documentation and this is what I did.

This is the function that needs to run periodically

@Scheduled(fixedDelayString = "300000")
@SchedulerLock(name = "onlineIngestionTask", lockAtMostFor = 240000, lockAtLeastFor = 240000)
public void pullTasksFromRemote() {
        //Code
}

In my config class I have the following beans

@Bean
public ScheduledLockConfiguration taskScheduler(LockProvider lockProvider) {
    return ScheduledLockConfigurationBuilder
        .withLockProvider(lockProvider)
        .withPoolSize(10)
        .withDefaultLockAtMostFor(Duration.ofMinutes(10))
        .build();
}



@Bean
public LockProvider lockProvider(DataSource dataSource) {
    return new JdbcTemplateLockProvider(dataSource);
}

The pom includes

<dependency>
    <groupId>net.javacrumbs.shedlock</groupId>
    <artifactId>shedlock-spring</artifactId>
    <version>0.14.0</version>
</dependency>

<dependency>
    <groupId>net.javacrumbs.shedlock</groupId>
    <artifactId>shedlock-provider-jdbc-template</artifactId>
    <version>0.14.0</version>
</dependency>

I added a table to my db, the one to which jdbc connects.

CREATE TABLE shedlock(
    name VARCHAR(64), 
    lock_until TIMESTAMP(3) NULL, 
    locked_at TIMESTAMP(3) NULL, 
    locked_by  VARCHAR(255), 
    PRIMARY KEY (name)
) 

After this I tried to test the functionality by running tha pp first on port 8080. Then I use server.port=9000 to run it again on port 9000. But both these instances start running the task. Am I missing something. Is something wrong in the implementation? Can someone give any ideas. Thanks !!

Answer 1

dlock guarantees to have one lock at any time by using database indexes and constraints. You can simply do something like below.

@Scheduled(cron = "30 30 3 * * *")
@TryLock(name = "onlineIngestionTask", owner = SERVER_NAME, lockFor = 240000)
public void pullTasksFromRemote() {

}

See the article about using it.

Answer 2

we recently had this issue in prod where we could see multiple runs of shedlock schedulers. if you are using spring boot 2.2.1.RELEASE onwards then use below deps for shedlock

<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-spring</artifactId>
<version>4.9.3</version>
</dependency>

    <dependency>
        <groupId>net.javacrumbs.shedlock</groupId>
        <artifactId>shedlock-provider-redis-spring</artifactId>
        <version>4.8.0</version>
    </dependency>

Answer 3

Please try with cron expression inside @scheduled instead of fixedDelayString, below scheduler run every hour.

@Scheduled(cron = "0 */1 * * *")