Typically when you are using Spring Cloud Eureka for service discovery and you shut down an instance that is registered with the server that instance is removed from the registry. However in some cases that might not be happen and instead the instance is just marked as being DOWN. If you look at your Eureka dashboard you will see something like this.

Eureka Dashboard

Notice one of the RACES services is marked as down and the big red text above the table. You might run into this because by default if 85% of instances in Eureka are not sending heartbeats to the Eureka server than the server will not evict them. When you see this, Eureka has entered what is called “self preservation mode”. The good news is you should not be alarmed by this. It is actually Eureka trying to be helpful and by not evicting instances that are not actually down. For example, there could be some network issues preventing instances from sending heartbeat information. Everything is still functioning correctly, so do you really want Eureka to start evicting instances? Probably not. With any luck the network issues will resolve themselves and heartbeat information will eventually be received by the server.

If for whatever reason you want to turn off self preservation mode you can set eureka.server.enableSelfPreservation to false. For a more in depth discussion on Eureka’s self preservation mode check out this question on Stack Overflow.

Ryan J Baxter

Husband, Father, Software Engineer