• show usage of Spring Boot and the Quartz-Scheduler
• enable cluster mode for Quartz Jobs in Spring Boot
• Provide docker-compose file to start a realistic cluster
• use PostgreSQL to demonstrate JDBC Store and concurrent job execution

This demo uses Flyway to populate the database. Including the Quartz required tables mean you need to make Flyway aware of those scripts. In the demo we copied it. It's source:

Quartz Postgres Scripts

quartz-2.3.2.jar!/org/quartz/impl/jdbcjobstore/tables_postgres.sql

If you just run the QuartzDemoApplication.kt Spring-Boot Application you need to start the database first, using run-postgres.sh

Open localhost to view the state of the application.

The docker-compose.yaml allows you to spin up the database and 3 instances of the quartz-demo application.

You need to build the image first mvn cerify

and then use docker-compose up -d to start the cluster.

You can browse each instance by itself or open /frames which will create a page with 3 iframes showing each instance side-by-side.

• http://www.quartz-scheduler.org/documentation/quartz-2.3.0/tutorials/tutorial-lesson-06.html
• http://www.quartz-scheduler.org/documentation/quartz-2.3.0/tutorials/crontrigger.html
• Cron Expressions Generator

Every instance of the application will start with two properties:

INST_NAME: "anyNumer-somename"
INST_WAITMILLIS: 25000

INST_NAME is used to identify the instance of the application in the cluster - it is used for logging and creating the Job keys and information.

INST_WAITMILLIS is used to allow every instance of the application to execute the Jobs slower than other nodes - if you want to play around with overlapping job execution times.

Watch out for the concurrent jobs (the might just run several times, even on the same node - especially if the jobs overlap - meaning they execute faster than they complete, so the next execution starts before the last one finished). A different behaviour is shown with the non-concurrent variation of the job (look out for the DisallowConcurrentExecution annotation!)

You can still use the Scheduled annotation from spring - but be aware that all instances will run them (might still be useful for some use-cases).

If you pause the scheduler, this will only affect that one instance of the application. The others still run.

To stop all processing you can stop all the triggers - this will affect the whole cluster.

JobListener only fire on the instance that was executing the job as well.

The Order66 Button creates an order (not a Quartz feature, it is meant to represent some sort of item that needs processing). With every order there is also a quartz job and trigger created. The Job execution is then distributed within the cluster by quartz.

There are options if the quartz scheduler cannot be used.

• JobRunr on GitHub - The ultimate library for background processing in Java. Distributed and backed by persistent storage. Open-source and free for commercial use.Alternative for Spring Batch and Quartz Scheduler. Hangfire for Java. Java CRON scheduler.
• SchedLock
  • https://suchit-g.medium.com/use-spring-scheduler-in-clustered-environment-9de27251763f
  • https://github.com/lukas-krecan/ShedLock