Spring boot app gracefully catch the SIGTERM signal and invoke the predestroy method

Question

I have a spring boot application which needs to clear or clean up the resources when we kill the process using kill pid. @predestroy annotated method is not working and not getting called. Please suggest how can we catch the SIGTERM and invoke the predestroy method

Answer 1

Ideally, it should work but make sure SIGTERM is called and not SIGKILL

I have a few cases where we run spring boot application

Docker

When you execute docker stop what happens behind the scene is

Stop one or more running containers The main process inside the container will receive SIGTERM, and after a grace period, SIGKILL

kill

kill 9955 => SIGTERM is called kill -9 9955 => SIGKILL is called

Refer here for more detail on kill.

Now coming back to @PreDestroy

I have added following line in my SpringBoot Application

@PreDestroy
public void tearDown() {
    System.out.println("Shutting Down...............the ");
}

I get following output when I do kill portno

2019-01-04 10:52:44.776  INFO o.s.s.c.ThreadPoolTaskScheduler / shutdown - 208 : Shutting down ExecutorService 'taskScheduler'
2019-01-04 10:52:44.783  INFO o.s.s.c.ThreadPoolTaskExecutor / shutdown - 208 : Shutting down ExecutorService 'applicationTaskExecutor'
2019-01-04 10:52:44.785  INFO o.s.o.j.LocalContainerEntityManagerFactoryBean / destroy - 597 : Closing JPA EntityManagerFactory for persistence unit 'default'
2019-01-04 10:52:44.792  INFO c.z.h.HikariDataSource / close - 350 : HikariPool-1 - Shutdown initiated...
2019-01-04 10:52:44.800  INFO c.z.h.HikariDataSource / close - 352 : HikariPool-1 - Shutdown completed.
Shutting Down...............

As you can see in Log I have 2 Scheduler Task running and JPA Entity Manager. On receiving SIGTERM it closes all that first and finally call preDestory.

I am not sure what more clean up you need to do but do make sure if its already cleaned.

Shut down embedded servlet container gracefully

You can also customize and write your own shutdown gracefully hook. Refer to this good discussion and sample code on this

Restructure embedded web server packages

Pls be mindful of the sample code from above link. If you are using newer version of Springboot chances are package might be missing.

Refer this for more detail on changes methods and classes

Answer 2

Just small addition to @MyTwoCents answer for @PreDestroy and Docker -> ensure to use ENTRYPOINT instead of CMD or RUN - only then you will run application as a main process and SIGTERM will be sent to your application