why must eureka.client.serviceUrl.defaultZone be provided in `bootstrap.properties` when config the spring cloud config server in a discovery manner?

Question

I was aiming to config the location of spring cloud config server by setting spring.applicaton.name and server.port and eureka.client.serviceUrl.defaultZone in application.properties together with spring.cloud.config.discovery.enabled=true and spring.cloud.config.discovery.service-id=cloud-config in bootstrap.properties, which turned out to be insufficient. The following error messages are shown in log:'

    com.netflix.discovery.DiscoveryClient    : DiscoveryClient_BOOTSTRAP/192.168.1.5:bootstrap - was unable to refresh its cache! status = Cannot execute request on any known server

    No instances found of configserver (cloud-config)

According to the docs, I moved eureka.client.serviceUrl.defaultZone into bootstrap.properties and succeeded.

My question is, if spring.application.name and server.port are essential for a eureka client to register on the eureka server, why they can be unsettled in bootstrap.properties for the config client?

I suspect that the config client will first use eureka.client.serviceUrl.defaultZone alone to connect with the eureka server and fetch service registration informations but not register itself so as to locate the config server and pull something. After that, since the config client is also a eureka client, it uses relative parameters in application.properties to register on eureka server. As some evidence of my suspect, I found the following logs during the startup of the application:

    2017-09-07 06:13:09.651  INFO [bootstrap,,,] 74104 --- [  restartedMain] com.netflix.discovery.DiscoveryClient    : Getting all instance registry info from the eureka server
    2017-09-07 06:13:09.817  INFO [bootstrap,,,] 74104 --- [  restartedMain] com.netflix.discovery.DiscoveryClient    : The response status is 200
    2017-09-07 06:13:09.821  INFO [bootstrap,,,] 74104 --- [  restartedMain] com.netflix.discovery.DiscoveryClient    : Not registering with Eureka server per configuration

    2017-09-07 06:13:37.427  INFO [-,,,] 74104 --- [  restartedMain] com.netflix.discovery.DiscoveryClient    : Getting all instance registry info from the eureka server

Is it?