EMERGENCY! EUREKA MAY BE INCORRECTLY CLAIMING INSTANCES ARE UP WHEN THEY'RE NOT. RENEWALS ARE LESSER THAN THRESHOLD AND HENCE THE INSTANCES ARE NOT BEING EXPIRED JUST TO BE SAFE.
Eureka server和client之间每隔30秒会进行一次心跳通信,告诉server,client还活着
在某一些时候注册在Eureka的服务已经挂掉了,但是服务却还留在Eureka的服务列表的情况。