从前面的章节我们大致的理解了Spring Cloud Ribbon的运行原理。Ribbon是一个客户端的负载均衡器，自己提供了一整套负载均衡的策略供大家使用，其默认的配置RibbonClientConfiguration里面定义了默认的负载均衡策略(IRule)，Ribbon实例检查策略(IPing)，服务实例清单的维护机制(ServerList<Server>)，负载均衡器(ILoadBalancer)等。

在spring-cloud-netflix-eureka-client包中的/META-INF/spring.factories中有一个如下的配置

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.cloud.netflix.ribbon.eureka.RibbonEurekaAutoConfiguration,\

这里的RibbonEurekaAutoConfiguration配置就是ribbon与Eureka集成的关键，先看里面的源码

@Configuration(proxyBeanMethods = false)
@EnableConfigurationProperties
@ConditionalOnRibbonAndEurekaEnabled
//本配置执行后才执行Ribbon的配置【重要】
@AutoConfigureAfter(RibbonAutoConfiguration.class)
//此处设置了Ribbon客户端的默认配置
@RibbonClients(defaultConfiguration = EurekaRibbonClientConfiguration.class)
public class RibbonEurekaAutoConfiguration {
}

EurekaRibbonClientConfiguration

@Configuration(proxyBeanMethods = false)
public class EurekaRibbonClientConfiguration {

    private static final Log log = LogFactory
            .getLog(EurekaRibbonClientConfiguration.class);

    @Value("${ribbon.eureka.approximateZoneFromHostname:false}")
    private boolean approximateZoneFromHostname = false;

    @RibbonClientName
    private String serviceId = "client";

    @Autowired(required = false)
    private EurekaClientConfig clientConfig;

    @Autowired(required = false)
    private EurekaInstanceConfig eurekaConfig;

    @Autowired
    private PropertiesFactory propertiesFactory;

    public EurekaRibbonClientConfiguration() {
    }

    public EurekaRibbonClientConfiguration(EurekaClientConfig clientConfig,
            String serviceId, EurekaInstanceConfig eurekaConfig,
            boolean approximateZoneFromHostname) {
        this.clientConfig = clientConfig;
        this.serviceId = serviceId;
        this.eurekaConfig = eurekaConfig;
        this.approximateZoneFromHostname = approximateZoneFromHostname;
    }

    //将覆盖Ribbon中的默认配置
    @Bean
    @ConditionalOnMissingBean
    public IPing ribbonPing(IClientConfig config) {
        if (this.propertiesFactory.isSet(IPing.class, serviceId)) {
            return this.propertiesFactory.get(IPing.class, config, serviceId);
        }
        NIWSDiscoveryPing ping = new NIWSDiscoveryPing();
        ping.initWithNiwsConfig(config);
        return ping;
    }
    //将覆盖Ribbon中的默认配置【服务实例清单的维护机制】
    @Bean
    @ConditionalOnMissingBean
    public ServerList<?> ribbonServerList(IClientConfig config,
            Provider<EurekaClient> eurekaClientProvider) {
        if (this.propertiesFactory.isSet(ServerList.class, serviceId)) {
            return this.propertiesFactory.get(ServerList.class, config, serviceId);
        }
        DiscoveryEnabledNIWSServerList discoveryServerList = new DiscoveryEnabledNIWSServerList(
                config, eurekaClientProvider);
        DomainExtractingServerList serverList = new DomainExtractingServerList(
                discoveryServerList, config, this.approximateZoneFromHostname);
        return serverList;
    }

    //将覆盖Ribbon中的默认配置
    @Bean
    public ServerIntrospector serverIntrospector() {
        return new EurekaServerIntrospector();
    }

    @PostConstruct
    public void preprocess() {
        String zone = ConfigurationManager.getDeploymentContext()
                .getValue(ContextKey.zone);
        if (this.clientConfig != null && StringUtils.isEmpty(zone)) {
            if (this.approximateZoneFromHostname && this.eurekaConfig != null) {
                String approxZone = ZoneUtils
                        .extractApproximateZone(this.eurekaConfig.getHostName(false));
                log.debug("Setting Zone To " + approxZone);
                ConfigurationManager.getDeploymentContext().setValue(ContextKey.zone,
                        approxZone);
            }
            else {
                String availabilityZone = this.eurekaConfig == null ? null
                        : this.eurekaConfig.getMetadataMap().get("zone");
                if (availabilityZone == null) {
                    String[] zones = this.clientConfig
                            .getAvailabilityZones(this.clientConfig.getRegion());
                    // Pick the first one from the regions we want to connect to
                    availabilityZone = zones != null && zones.length > 0 ? zones[0]
                            : null;
                }
                if (availabilityZone != null) {
                    // You can set this with archaius.deployment.* (maybe requires
                    // custom deployment context)?
                    ConfigurationManager.getDeploymentContext().setValue(ContextKey.zone,
                            availabilityZone);
                }
            }
        }
        //调用Ribbon的工具类
        RibbonUtils.initializeRibbonDefaults(serviceId);
    }
}

在Eurek中通过覆盖Ribbon默认的IPing 、ServerList<?>以及ServerIntrospector的配置后，成功的与Ribbon的处理逻辑整合在一起，从而实现使用Eureka中的服务来完成负载均衡的目的。