Eureka registers with each other, only showing each other or only showing problems in one

In the use of eureka When writing a microservice program , There's a problem , It's in two eureka_server When registering with each other , Every eureka Or only show each other , Or only show in one .

The two configurations are as follows ：

#  Configure service name  ==  Registry Center server
spring.application.name=eureka_server_copy

#  Service port number 
server.port=7000

#  Configure the service instance ip
eureka.instance.hostname=localhost
# Whether or not to eureka Register with the registry ( This self registration )

eureka.client.register-with-eureka=true

# Whether from eureka Get the registered address in （ Background has ip Display instead of domain name ）
eureka.client.fetch-registry=false

#  To configure eureka Information about the server to which the client is connected 
eureka.client.service-url.defaultZone=http://localhost:9000/eureka/,http://localhost:7000/eureka/

#  Configure service name  ==  Registry Center server
spring.application.name=eureka_server

#  Service port number 
server.port=9000

#  Configure the service instance ip
eureka.instance.hostname=localhost



# Whether or not to eureka Register with the registry ( This self registration )

#  Register yourself in the registry 
eureka.client.register-with-eureka=true

# Whether from eureka Get the registered address in （ Background has ip Display instead of domain name ）
eureka.client.fetch-registry=false

#  To configure eureka Information about the server to which the client is connected 
eureka.client.service-url.defaultZone=http://localhost:7000/eureka/,http://localhost:9000/eureka/

I modified eureka.client.service-url.defaultZone The order of addresses , When the port of this machine is in front , Only show each other's , Don't show yourself , When the address of the local port is in the back, it is only displayed on one ：

The reason for this result is that the hostname is the same and localhost As the registered address ：

#  Configure the service instance ip
eureka.instance.hostname=localhost 

eureka.client.service-url.defaultZone=http://localhost:9000/eureka/,http://localhost:7000/eureka/

The reasons why registration centers cannot register with each other in the above two cases , Name the host name randomly , Use 172.0.0.1 Instead of localhost that will do ：

eureka.instance.hostname=machine2



# Whether or not to eureka Register with the registry ( This self registration )

eureka.client.register-with-eureka=true

# Whether from eureka Get the registered address in （ Background has ip Display instead of domain name ）
eureka.client.fetch-registry=false

#  To configure eureka Information about the server to which the client is connected 
eureka.client.service-url.defaultZone=http://127.0.0.1:9000/eureka/,http://127.0.0.1:7000/eureka/

After modification, you can register with each other ：