How can I execute only once a scheduled task inside a cluster using Spring boot?

Question

I have a scheduled task in my web-app developed using spring boot. I run it on a tomcat cluster, so at hour X the scheduled task start from every node.

I read about: https://github.com/lukas-krecan/ShedLock, so I followed the guide, but it doesn't work.. Here what I have done:

I included these dependency in my pom:

  <dependency>
        <groupId>net.javacrumbs.shedlock</groupId>
        <artifactId>shedlock-spring</artifactId>
        <version>0.18.2</version>
    </dependency>       
    <dependency>
        <groupId>net.javacrumbs.shedlock</groupId>
        <artifactId>shedlock-provider-jdbc</artifactId>
        <version>0.18.2</version>
    </dependency>

Then I added this to my method:

@Transactional(value="transactionManagerClienti",readOnly=false)
@Scheduled(cron="0 03 7,10,13,15 * * MON-FRI")
@SchedulerLock(name = "syncCliente"
@Override
public void syncCliente() {
  ....
}

then where I config the datasource I did:

@Configuration
@EnableJpaRepositories(basePackages = {"it.repository"}, entityManagerFactoryRef="entityManager", transactionManagerRef="transactionManager")
public class DataSourceMuxConfig {

    @Autowired
    private Environment environment;

    @Primary
    @Bean(name = "dataSource")
    @ConfigurationProperties(prefix = "spring.datasource.mux")
    public DataSource dataSource() throws NamingException {
        if(Arrays.asList(environment.getActiveProfiles()).contains("dev")) {
            return DataSourceBuilder.create().build();
        }else {
            Context ctxConfig = new InitialContext();
            return (DataSource) ctxConfig.lookup("java:comp/env/jdbc/mux");
        }
    }

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

and this my schedule config:

@Configuration
@EnableScheduling
@EnableAsync
public class SchedulerConfig implements SchedulingConfigurer {

    @Override
    public void configureTasks(ScheduledTaskRegistrar taskRegistrar) {
        taskRegistrar.setScheduler(taskExecutor());
    }

    @Bean(destroyMethod = "shutdown")
    public Executor taskExecutor() {
        return Executors.newScheduledThreadPool(10);
    }

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

}

but it doesn't work.

Each node of the cluster excute at the same time this scheduled task. Why?

How can I avoid to execute multiple times a task at the same time with spring boot?

Answer 1

I've recently implemented a simple annotation library, dlock, to execute a scheduled task only once over multiple nodes. You can simply do something like below.

@Scheduled(cron = "59 59 8 * * *" /* Every day at 8:59:59am */)
@TryLock(name = "emailLock", owner = NODE_NAME, lockFor = TEN_MINUTE)
public void sendEmails() {
  List<Email> emails = emailDAO.getEmails();
  emails.forEach(email -> sendEmail(email));
}

Please see the Github page for full configuration.