Graceful Shutdown of Spring Boot Services and the Risks of Using kill -9

kill sends signals to processes; the default SIGTERM (15) terminates gracefully, while SIGKILL (9) forces immediate termination. Using kill -9 on services such as a Spring Boot application can cause data loss similar to a sudden power outage, especially with non‑transactional storage engines.

Examples illustrate how a transaction on MyISAM can become inconsistent when a process is killed, and why distributed systems must avoid abrupt termination.

For a more graceful stop, kill -15 can be used. The article provides a simple controller that sleeps for 100 seconds and shows that sending kill -15 to the process interrupts the thread, causing an InterruptedException but still allowing cleanup.

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

Spring Boot also offers built‑in shutdown scripts (shutdown.sh/shutdown.bat) and the Actuator shutdown endpoint, which can be enabled in application.yml and invoked via HTTP.

server:
  port: 9988
management:
  endpoints:
    web:
      exposure:
        include: shutdown
  endpoint:
    shutdown:
      enabled: true

For advanced control, the article introduces an ElegantShutdownConfig that customizes the Tomcat connector, pauses new requests, and waits up to a configurable timeout before forcing termination.

public class ElegantShutdownConfig implements TomcatConnectorCustomizer, ApplicationListener
{
    private volatile Connector connector;
    private final int waitTime = 10;
    @Override
    public void customize(Connector connector) { this.connector = connector; }
    @Override
    public void onApplicationEvent(ContextClosedEvent event) {
        connector.pause();
        Executor executor = connector.getProtocolHandler().getExecutor();
        if (executor instanceof ThreadPoolExecutor) {
            ThreadPoolExecutor threadPoolExecutor = (ThreadPoolExecutor) executor;
            threadPoolExecutor.shutdown();
            if (!threadPoolExecutor.awaitTermination(waitTime, TimeUnit.SECONDS)) {
                System.out.println("Please try forceful shutdown");
            }
        }
    }
}

Finally, the article shows how to execute backup logic during shutdown using the @PreDestroy annotation in a Spring bean.

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

These techniques together provide a safe, graceful way to stop Spring Boot services without risking data corruption.