Spring and scheduled tasks on multiple instances

The Spring - ShedLock project is specifically created to achieve this.

Dependency -

<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-spring</artifactId>    

Configuration -

@EnableScheduling
@EnableSchedulerLock(defaultLockAtMostFor = "PT30S")

Implementation -

@Scheduled(cron = "0 0/15 * * * ?")
@SchedulerLock(name = "AnyUniqueName", 
  lockAtLeastForString = "PT5M", lockAtMostForString = "PT10M")
public void scheduledTask() {
    // ...
}

This setup will make sure that exactly one instance should run the scheduled task.

If you want only a specific instance should run the Scheduler task,

You need to config your scheduler to use the properties file and control the Scheduler switch like this -

@ConditionalOnProperty(
  value = "scheduling.enabled", havingValue = "true", matchIfMissing = true
)
@Configuration
@EnableScheduling
@EnableSchedulerLock(defaultLockAtMostFor = "PT30S")
public class SchedulingConfig {

Now, you need to provide a property scheduling.enabled = true in your application.properties file, for the instance from which you want Schedular to be run.

Follow this link for complete implementation.

This is a very wide topic. And there are many options to achieve this.

1. You can configure your application to have multiple profiles. For example use another profile 'cron' . And start your application on only one server with this profile. So for example, on a production environment you have three servers (S1, S2, S3), then you could run on S1 with profile prod and cron(-Dspring.profiles.active=prod,cron). And on S2 and S3 just use prod profile(-Dspring.profiles.active=prod).

   And in code, you can use @Profile("cron") on scheduler classes. This way it will be executed only when cron profile is active

2. Use a distributed lock. If you have Zookeeper in your environment, you can use this to achieve distributed locking system.

3. You can use some database(mysql) and create a sample code to get a lock on one of the table and add an entry. And whichever instance gets the lock, will make an entry in this database and will execute the cron job. You need to put a check in your code, if getLock() is successfull only then proceed with execution. Mysql has utilities like LOCK TABLES, which you could use to get away with concurrent read/writes.

personally I would say, option 2 is the best of all.