Graceful Shutdown of Spring Boot Applications: Avoiding the Pitfalls of kill -9

The Linux kill -9 pid command forcefully terminates a process, which is equivalent to an abrupt power loss; when used on services that handle transactions (e.g., MySQL InnoDB vs. MyISAM) it can lead to data loss or inconsistency, especially in distributed systems.

Because kill -9 does not allow the application to release resources or finish ongoing work, the article recommends using more graceful termination signals such as kill -15 pid, which sends SIGTERM and gives the JVM a chance to shut down cleanly.

For Spring Boot applications, three graceful shutdown approaches are presented:

Calling the Tomcat shutdown script ( shutdown.bat/shutdown.sh) to stop the container.

Enabling the Actuator shutdown endpoint in application.yml and invoking it via HTTP.

Implementing a custom ElegantShutdownConfig that pauses the Tomcat connector, waits for thread‑pool termination, and then closes the context.

Example controller used for testing:

@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";
}

Custom shutdown configuration class:

public class ElegantShutdownConfig implements TomcatConnectorCustomizer, ApplicationListener<ContextClosedEvent> {
    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 pool = (ThreadPoolExecutor) executor;
            pool.shutdown();
            if (!pool.awaitTermination(waitTime, TimeUnit.SECONDS)) {
                System.out.println("Please try forceful shutdown");
            }
        }
    }
}

Additionally, the article mentions using the @PreDestroy annotation to perform backup or cleanup tasks before the JVM exits.

Overall, the guide advises avoiding kill -9 in production, preferring graceful termination methods that allow Spring Boot services to finish in‑flight requests, release resources, and maintain data integrity.