image.png

正如大家在图中所看到的那样，eureka定义了5个监听事件，分别是：

EurekaServerStartedEvent - Eureka服务端启动事件
EurekaRegistryAvailableEvent - Eureka服务端可用事件
EurekaInstanceRegisteredEvent - Eureka客户端服务注册事件
EurekaInstanceRenewedEvent - Eureka客户端续约事件
EurekaInstanceCanceledEvent - Eureka客户端下线事件

通过查看代码我们可以发现EurekaInstanceRegisteredEvent 和EurekaServerStartedEvent事件会在eureka服务启动后被触发。
首先触发Eureka服务器EurekaInstanceRegisteredEvent，然后判断如果eureka服务器已经在运行，则触发EurekaServerStartedEvent。

    @Override
    public void start() {
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    //TODO: is this class even needed now?
                    eurekaServerBootstrap.contextInitialized(EurekaServerInitializerConfiguration.this.servletContext);
                    log.info("Started Eureka Server");

                    publish(new EurekaRegistryAvailableEvent(getEurekaServerConfig()));
                    EurekaServerInitializerConfiguration.this.running = true;
                    publish(new EurekaServerStartedEvent(getEurekaServerConfig()));
                }
                catch (Exception ex) {
                    // Help!
                    log.error("Could not initialize Eureka servlet context", ex);
                }
            }
        }).start();
    }

这两个事件不是我们的重点，我们来看一下剩余的三个事件。

EurekaInstanceRegisteredEvent 该事件在每次有微服务进行注册时触发。

    private void handleRegistration(InstanceInfo info, int leaseDuration,
            boolean isReplication) {
        log("register " + info.getAppName() + ", vip " + info.getVIPAddress()
                + ", leaseDuration " + leaseDuration + ", isReplication "
                + isReplication);
        publishEvent(new EurekaInstanceRegisteredEvent(this, info, leaseDuration,
                isReplication));
    }

EurekaInstanceRenewedEvent续约事件

    public boolean renew(final String appName, final String serverId,
            boolean isReplication) {
        log("renew " + appName + " serverId " + serverId + ", isReplication {}"
                + isReplication);
        List<Application> applications = getSortedApplications();
        for (Application input : applications) {
            if (input.getName().equals(appName)) {
                InstanceInfo instance = null;
                for (InstanceInfo info : input.getInstances()) {
                    if (info.getId().equals(serverId)) {
                        instance = info;
                        break;
                    }
                }
                publishEvent(new EurekaInstanceRenewedEvent(this, appName, serverId,
                        instance, isReplication));
                break;
            }
        }
        return super.renew(appName, serverId, isReplication);
    }

EurekaInstanceCanceledEvent客户端下线触发事件

    private void handleCancelation(String appName, String id, boolean isReplication) {
        log("cancel " + appName + ", serverId " + id + ", isReplication " + isReplication);
        publishEvent(new EurekaInstanceCanceledEvent(this, appName, id, isReplication));
    }

通过对这5个事件进行监听，我们可以实现注册中心报警

@Component
public class EurekaStateChangeListener {
    
    @EventListener
    public void listen(EurekaInstanceCanceledEvent eurekaInstanceCanceledEvent) {
        //服务断线事件
        String appName = eurekaInstanceCanceledEvent.getAppName();
        String serverId = eurekaInstanceCanceledEvent.getServerId();
        System.out.println(appName);
        System.out.println(serverId);

        System.out.println("EurekaInstanceCanceledEvent");

    }
 
    @EventListener
    public void listen(EurekaInstanceRegisteredEvent event) {
        InstanceInfo instanceInfo = event.getInstanceInfo();
        System.out.println(instanceInfo);

        System.out.println("EurekaInstanceRegisteredEvent");

    }
 
    @EventListener
    public void listen(EurekaInstanceRenewedEvent event) {
        event.getAppName();
        event.getServerId();
        System.out.println("EurekaInstanceRenewedEvent");


    }
 
    @EventListener
    public void listen(EurekaRegistryAvailableEvent event) {
        System.out.println("EurekaRegistryAvailableEvent");

    }
 
    @EventListener
    public void listen(EurekaServerStartedEvent event) {

        System.out.println("EurekaServerStartedEvent");
        //Server启动
    }
}