服务之优雅停机_shutdown immediate graceful

1 服务停机

服务优雅停机分运维层面和应用层面，在这里主要讲一下应用层面的优雅停机，这里讲到的实现方式和案例均是在springboot项目下。

2 优雅停机的三种方式

2.1 spring-boot 2.3.1以上版本

springboot支持应用的优雅停机，当应用接收到kill的信号（15 终止号令）时，会停止接收新的请求，并等待活跃的请求完成后，关闭服务，通过yml文件配置：

server:
  shutdown: graceful   //IMMEDIATE立即停机（默认值）、GRACEFUL 
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shutdown配置介绍：

GRACEFUL：should support graceful shutdown, allowing active requests time to complete.
IMMEDIATE：should shut down immediately.

但是需要注意的事，该种方式只对web请求所产生的线程有效，应用内新建立的线程无效（只要活跃的请求完成，即使应用内有线程存活，依然会立即关闭）。

2.2 tomcat方式

优雅停机效果同springboot2.3.1.

@Component
@Slf4j
public class GracefulShutdownTomcat implements TomcatConnectorCustomizer, ApplicationListener<ContextClosedEvent> {

    private volatile Connector connector;
    private final int waitTime = 30;

    @Override
    public void customize(Connector connector) {
        this.connector = connector;
    }

    @Override
    public void onApplicationEvent(ContextClosedEvent event) {
        this.connector.pause();
        log.info("active Thread count: {}", Thread.activeCount());
        Executor executor = this.connector.getProtocolHandler().getExecutor();
        if (executor instanceof ThreadPoolExecutor) {
            ThreadPoolExecutor threadPoolExecutor = (ThreadPoolExecutor)executor;
            threadPoolExecutor.shutdown();
            try {
                if (!threadPoolExecutor.awaitTermination(waitTime, TimeUnit.SECONDS)) {
                    log.warn("Tomcat thread pool did't shut down gracefully within" + waitTime + " seconds. Proceeding with forceful shutdown");
                }
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
            }
        }
    }

    @Bean
    public ConfigurableServletWebServerFactory servletContainer(final GracefulShutdownTomcat gracefulShutdownTomcat) {
        TomcatServletWebServerFactory tomcat = new TomcatServletWebServerFactory();
        tomcat.addConnectorCustomizers(gracefulShutdownTomcat);
        return tomcat;
    }
}
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3 jvm

通过jvm的钩子监控kill信号，该种方式对应用内建立的线程池有效（会在设定的最大等待时间达到之前，一直等待线程执行完成，或到达最大时间停机），对web请求产生的线程暂时未找到等待方式，不过web用户请求一般都由运维在k8s和nginx层面进行路由处理。
另外需要注意终止方法调用的最大等待时间，要根据程序设计，提供一个合理的值，避免线程池中存在未执行完成的线程。

@Configuration
public class ShutdownHook {

    public ShutdownHook() {
        Runtime.getRuntime().addShutdownHook(new Thread(() -> {
            ThreadPoolFactory.shutdown();
            try {
                ThreadPoolFactory.awaitTermination(30, TimeUnit.SECONDS);
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
            }
        }));
    }
}
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