1.什么是优雅停机

先来一段简单的代码，如下：

<pre style="box-sizing: border-box; outline: none; margin: 0px; padding: 0px; border: 0px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-variant-numeric: inherit; font-variant-east-asian: inherit; font-weight: 400; font-stretch: inherit; font-size: 18px; line-height: inherit; font-family: couriernew, courier, monospace; vertical-align: baseline; color: rgb(93, 93, 93); letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(255, 255, 255); text-decoration-style: initial; text-decoration-color: initial;">


@RestController
public class DemoController {
 @GetMapping("/demo")
 public String demo() throws InterruptedException {
     // 模拟业务耗时处理流程
  Thread.sleep(20 * 1000L);
  return "hello";
 }
}


</pre>

当我们流量请求到此接口执行业务逻辑的时候，若服务端此时执行关机（kill），spring boot 默认情况会直接关闭容器（tomcat 等），导致此业务逻辑执行失败。在一些业务场景下：会出现数据不一致的情况，事务逻辑不会回滚。

2.graceful shutdown

image

在最新的 spring boot 2.3 版本，内置此功能，不需要再自行扩展容器线程池来处理，目前 spring boot 嵌入式支持的 web 服务器（Jetty、Reactor Netty、Tomcat 和 Undertow）以及反应式和基于 Servlet 的 web 应用程序都支持优雅停机功能。我们来看下如何使用:

当使用 server.shutdown=graceful 启用时，在 web 容器关闭时，web 服务器将不再接收新请求，并将等待活动请求完成的缓冲期。

3.配置体验

image

此处支持的 shutdown 行为，我们看下源码枚举如下：

<pre style="box-sizing: border-box; outline: none; margin: 0px; padding: 0px; border: 0px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-variant-numeric: inherit; font-variant-east-asian: inherit; font-weight: 400; font-stretch: inherit; font-size: 18px; line-height: inherit; font-family: couriernew, courier, monospace; vertical-align: baseline; color: rgb(93, 93, 93); letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(255, 255, 255); text-decoration-style: initial; text-decoration-color: initial;">


/**
 * Configuration for shutting down a {@link WebServer}.
 *
 * @author Andy Wilkinson
 * @since 2.3.0
 */
public enum Shutdown {
 /**
  * 优雅停机 （限期停机）
  *
  */
 GRACEFUL,

 /**
  * 立即停机
  */
 IMMEDIATE;

}


</pre>

缓冲期 timeout-per-shutdown-phase 配置

默认时间为 30S, 意味着最大等待 30S，超时候无论线程任务是否执行完毕都会停机处理，一定要合理合理设置。

效果体验

请求服务端接口

image

执行关闭应用

image

服务端接到关闭指令

<pre style="box-sizing: border-box; outline: none; margin: 0px; padding: 0px; border: 0px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-variant-numeric: inherit; font-variant-east-asian: inherit; font-weight: 400; font-stretch: inherit; font-size: 18px; line-height: inherit; font-family: couriernew, courier, monospace; vertical-align: baseline; color: rgb(93, 93, 93); letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(255, 255, 255); text-decoration-style: initial; text-decoration-color: initial;">


2020-05-17 18:28:28.940  INFO 60341 --- [extShutdownHook] o.s.b.w.e.tomcat.GracefulShutdown        : Commencing graceful shutdown. Waiting for active requests to complete
2020-05-17 18:28:45.923  INFO 60341 --- [tomcat-shutdown] o.s.b.w.e.tomcat.GracefulShutdown        : Graceful shutdown complete


</pre>

接口请求执行完成

4.相关知识

4.1 关于此处执行kill -2 而不是 kill -9

kill -2 相当于快捷键 Ctrl + C 会触发 Java 的 ShutdownHook 事件处理（优雅停机或者一些后置处理可参考以下源码）

<pre style="box-sizing: border-box; outline: none; margin: 0px; padding: 0px; border: 0px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-variant-numeric: inherit; font-variant-east-asian: inherit; font-weight: 400; font-stretch: inherit; font-size: 18px; line-height: inherit; font-family: couriernew, courier, monospace; vertical-align: baseline; color: rgb(93, 93, 93); letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(255, 255, 255); text-decoration-style: initial; text-decoration-color: initial;">


//ApplicationContext
 @Override
 public void registerShutdownHook() {
  if (this.shutdownHook == null) {
   // No shutdown hook registered yet.
   this.shutdownHook = new Thread(SHUTDOWN_HOOK_THREAD_NAME) {
    @Override
    public void run() {
     synchronized (startupShutdownMonitor) {
      doClose();
     }
    }
   };
   Runtime.getRuntime().addShutdownHook(this.shutdownHook);
  }
 }


</pre>

kill -9，暴力美学强制杀死进程，不会执行 ShutdownHook

4.2 通过 actuator 端点实现优雅停机

POST 请求 /actuator/shutdown 即可执行优雅关机。

源码解析

<pre style="box-sizing: border-box; outline: none; margin: 0px; padding: 0px; border: 0px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-variant-numeric: inherit; font-variant-east-asian: inherit; font-weight: 400; font-stretch: inherit; font-size: 18px; line-height: inherit; font-family: couriernew, courier, monospace; vertical-align: baseline; color: rgb(93, 93, 93); letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(255, 255, 255); text-decoration-style: initial; text-decoration-color: initial;">


@Endpoint(id = "shutdown", enableByDefault = false)
public class ShutdownEndpoint implements ApplicationContextAware {

 @WriteOperation
 public Map<String, String> shutdown() {
  Thread thread = new Thread(this::performShutdown);
  thread.setContextClassLoader(getClass().getClassLoader());
  thread.start();
 }

 private void performShutdown() {
  try {
   Thread.sleep(500L);
  }
  catch (InterruptedException ex) {
   Thread.currentThread().interrupt();
  }

  // 此处close 逻辑和上边 shutdownhook 的处理一样
  this.context.close();
 }
}


</pre>