Eureka的server端會發出5個事件通知，分別是：

EurekaInstanceCanceledEvent 服務下線事件
EurekaInstanceRegisteredEvent 服務註冊事件
EurekaInstanceRenewedEvent 服務續約事件
EurekaRegistryAvailableEvent Eureka註冊中心啟動事件

EurekaServerStartedEvent Eureka Server啟動事件

@Component
public class EurekaStateChangeListener {

    @Autowired
    private EmailLogService emailLogService;

    @EventListener
    public void listen(EurekaInstanceCanceledEvent eurekaInstanceCanceledEvent) {

        String appName = eurekaInstanceCanceledEvent.getAppName();
        String serverId = eurekaInstanceCanceledEvent.getServerId();
        System.out.println(appName);
        System.out.println(serverId);
        String message = LocalDateTime.now()+"\r\n"+appName+"\r\n"+serverId;
        emailLogService.sendMail(message);

    }
}