Replication Issue in Eureka Cluster

[Buwanaka Herath]

We are currently facing an issue related to Eureka replication and please refer to the following details for the background of the issue:

• We have two Eureka servers working as primary and secondary which was recently upgraded to spring boot 2.0.4
  
• The secondary eureka is supposed to be the active eureka server only when the primary is down/unavailable
  
• And we have a set of micro-services which registers to the Eureka
  
• Two of the micro-services were also upgraded to spring boot 2.0.4 recently where as all the others are still on spring boot 1.4.5 version.
  
• Suppose we have 8 instances per micro-service, usually when we deploy a micro-service we can see all 8 instances registered on each Eureka server(both primary and secondary).
  
• The above case is true for all the micro-services in spring boot 1.4.5 even now. 
  
• But when we deploy any one of the upgraded micro-services, we can see all 8 instances registered on the primary eureka server, but on the secondary eureka we can see only 2-6 instances registered unless we restart the secondary eureka.
  
• Then we tested the scenario after shutting down the primary eureka, and what we observed was that right after the primary is shutdown the secondary kicks in without an issue and all 8 instances appear. which means this is not functionally affecting so far for the mentioned cases.