在启动eureka的之后，启动其他的eureka的服务注册进来之后会出现如下的异常

Caused by: org.apache.http.conn.ConnectTimeoutException: Connect to localhost:8761 timed out
	at org.apache.http.conn.scheme.PlainSocketFactory.connectSocket(PlainSocketFactory.java:123) ~[httpclient-4.5.6.jar:4.5.6]
	at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:180) ~[httpclient-4.5.6.jar:4.5.6]
	at org.apache.http.impl.conn.AbstractPoolEntry.open(AbstractPoolEntry.java:144) ~[httpclient-4.5.6.jar:4.5.6]
	at org.apache.http.impl.conn.AbstractPooledConnAdapter.open(AbstractPooledConnAdapter.java:134) ~[httpclient-4.5.6.jar:4.5.6]
	at org.apache.http.impl.client.DefaultRequestDirector.tryConnect(DefaultRequestDirector.java:610) ~[httpclient-4.5.6.jar:4.5.6]
	at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:445) ~[httpclient-4.5.6.jar:4.5.6]
	at org.apache.http.impl.client.AbstractHttpClient.doExecute(AbstractHttpClient.java:835) ~[httpclient-4.5.6.jar:4.5.6]
	at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:118) ~[httpclient-4.5.6.jar:4.5.6]
	at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:56) ~[httpclient-4.5.6.jar:4.5.6]
	at com.sun.jersey.client.apache4.ApacheHttpClient4Handler.handle(ApacheHttpClient4Handler.java:173) ~[jersey-apache-client4-1.19.1.jar:1.19.1]
	... 10 common frames omitted

造成的原因呢其实很简单，就是server的配置里面没有配置defaultzone

eureka:
  client:
    service-url:
      defaultZone: http://127.0.0.1:9001/eureka/

是因为在源码里面EurekaClientConfigBean类里面指定了defaultZone

package org.springframework.cloud.netflix.eureka;
import ...
@ConfigurationProperties("eureka.client")
public class EurekaClientConfigBean implements EurekaClientConfig {
    public static final String PREFIX = "eureka.client";
    public static final String DEFAULT_URL = "http://localhost:8761/eureka/";
    public static final String DEFAULT_ZONE = "defaultZone";
    private static final int MINUTES = 60;
    @Autowired(
        required = false
    )
    .....
    public EurekaClientConfigBean() {
        this.serviceUrl.put("defaultZone", "http://localhost:8761/eureka/");
        this.gZipContent = true;
        this.useDnsForFetchingServiceUrls = false;
        this.registerWithEureka = true;
        this.preferSameZoneEureka = true;
        this.availabilityZones = new HashMap();
        this.filterOnlyUpInstances = true;
        this.fetchRegistry = true;
        this.dollarReplacement = "_-";
        this.escapeCharReplacement = "__";
        this.allowRedirects = false;
        this.onDemandUpdateStatusChange = true;
        this.clientDataAccept = EurekaAccept.full.name();
        this.shouldUnregisterOnShutdown = true;
        this.shouldEnforceRegistrationAtInit = false;
    }
    ...
}