Graceful Shutdown of Spring Boot Services: Why kill -9 Is Dangerous and How to Stop Applications Properly

kill -9 pid ???

The kill command sends signals to processes; the default is SIGTERM (15). When a process does not stop, SIGKILL (9) can be used, but it forcefully terminates the process and may cause serious issues in production environments.

Problems Caused by kill -9 pid

Using kill -9 is equivalent to a sudden power loss. For example, if a transaction updates two tables and the process is killed, only one table may be updated, leading to data inconsistency, especially with MyISAM tables or distributed services.

In Java, a forced kill triggers an InterruptedException in sleeping threads, which can leave resources unreleased.

Graceful Shutdown Methods

kill -15 pid (SIGTERM)

Sending SIGTERM allows the application to handle shutdown logic. The article shows a simple Spring Boot controller that sleeps for 100 seconds and demonstrates that after sending kill -15 14086, the thread is interrupted and the method logs an exception.

@GetMapping("/test")
public String test() {
    log.info("test --- start");
    try { Thread.sleep(100000); } catch (InterruptedException e) { e.printStackTrace(); }
    log.info("test --- end");
    return "test";
}

Using Spring's ConfigurableApplicationContext

Implement ApplicationContextAware and call ((ConfigurableApplicationContext)context).close(); to stop the application.

public void shutdown() {
    ConfigurableApplicationContext ctx = (ConfigurableApplicationContext) context;
    ctx.close();
}

Spring Boot Actuator

Add the spring-boot-starter-actuator dependency and enable the shutdown endpoint in application.yml. A request to /actuator/shutdown returns a friendly message and stops the service.

management:
  endpoints:
    web:
      exposure:
        include: shutdown
  endpoint:
    shutdown:
      enabled: true

Custom Elegant Shutdown with Tomcat

Create a TomcatConnectorCustomizer that pauses the connector and waits for the thread pool to finish before the JVM exits.

public void onApplicationEvent(ContextClosedEvent event) {
    connector.pause();
    Executor executor = connector.getProtocolHandler().getExecutor();
    if (executor instanceof ThreadPoolExecutor) {
        ThreadPoolExecutor pool = (ThreadPoolExecutor) executor;
        pool.shutdown();
        if (!pool.awaitTermination(waitTime, TimeUnit.SECONDS)) {
            System.out.println("Please try forceful shutdown");
        }
    }
}

Data Backup on Shutdown

Annotate a bean method with @PreDestroy to execute backup logic before the container stops.

@PreDestroy
public void backData() {
    System.out.println("Backing up data...");
}

The article concludes that using graceful shutdown techniques avoids data loss, allows proper resource cleanup, and can be extended with custom backup actions.