前言

Gateway  Ribbon  Nacos分别属于不同组织开发的框架,但是能共同服务于微服务框架中,它们是如何配合的呢

Gateway

1.在自动配置类GatewayDiscoveryClientAutoConfiguration中有一段代码

    @Bean
        @ConditionalOnProperty(name = "spring.cloud.gateway.discovery.locator.enabled")
        public DiscoveryClientRouteDefinitionLocator discoveryClientRouteDefinitionLocator(
                ReactiveDiscoveryClient discoveryClient,
                DiscoveryLocatorProperties properties) {
            return new DiscoveryClientRouteDefinitionLocator(discoveryClient, properties);
        }

当spring.cloud.gateway.discovery.locator.enabled为true,这段代码会从ReactiveDiscoveryClient的实现类中获取服务名称列表封装成路由定义,而Nacos中有对应的实现类为NacosReactiveDiscoveryClient,这是它们的联系点之一

2.当外部请求进来时,例如https://host/服务名/xxx,会经过一个全局过滤器,为LoadBalancerClientFilter,这个过滤器的作用是将url的服务名称改成真正服务所在的ip,里面有段关键代码是

protected ServiceInstance choose(ServerWebExchange exchange) {
        return loadBalancer.choose(
                ((URI) exchange.getAttribute(GATEWAY_REQUEST_URL_ATTR)).getHost());
    }

上面起作用的是loadBalancer,对应的类型是LoadBalancerClient,这个是gateway框架定义的接口,真正实现类是Ribbon的RibbonLoadBalancerClient,这是gateway和ribbon的关联点

Ribbon

再来看看RibbonLoadBalancerClient的choose方法

public ServiceInstance choose(String serviceId, Object hint) {
        Server server = getServer(getLoadBalancer(serviceId), hint);
        if (server == null) {
            return null;
        }
        return new RibbonServer(serviceId, server, isSecure(server, serviceId),
                serverIntrospector(serviceId).getMetadata(server));
    }

上面关键代码是getLoadBalancer(serviceId),如下

protected ILoadBalancer getLoadBalancer(String serviceId) {
        return this.clientFactory.getLoadBalancer(serviceId);
    }

这段代码目的是取出ILoadBalancer的实现类,其为ZoneAwareLoadBalancer,而它又是继承DynamicServerListLoadBalancer,构造函数如下

public DynamicServerListLoadBalancer(IClientConfig clientConfig, IRule rule, IPing ping,
                                         ServerList<T> serverList, ServerListFilter<T> filter,
                                         ServerListUpdater serverListUpdater) {
        super(clientConfig, rule, ping);
        this.serverListImpl = serverList;
        this.filter = filter;
        this.serverListUpdater = serverListUpdater;
        if (filter instanceof AbstractServerListFilter) {
            ((AbstractServerListFilter) filter).setLoadBalancerStats(getLoadBalancerStats());
        }
        restOfInit(clientConfig);
    }

上面的构造函数会自动注入类型ServerList<T>的serverList,而nacos的NacosServerList实现了其接口,这里就是ribbon和nacos的连接点.

nacos

再来看看nacos什么时候提供了NacosServerList,看下面配置类

@Configuration(proxyBeanMethods = false)
@ConditionalOnRibbonNacos
public class NacosRibbonClientConfiguration {

    @Autowired
    private PropertiesFactory propertiesFactory;

    @Bean
    @ConditionalOnMissingBean
    public ServerList<?> ribbonServerList(IClientConfig config,
            NacosDiscoveryProperties nacosDiscoveryProperties) {
        if (this.propertiesFactory.isSet(ServerList.class, config.getClientName())) {
            ServerList serverList = this.propertiesFactory.get(ServerList.class, config,
                    config.getClientName());
            return serverList;
        }
        NacosServerList serverList = new NacosServerList(nacosDiscoveryProperties);
        serverList.initWithNiwsConfig(config);
        return serverList;
    }

    @Bean
    @ConditionalOnMissingBean
    public NacosServerIntrospector nacosServerIntrospector() {
        return new NacosServerIntrospector();
    }

}

在此配置类中,nacos提供了NacosServerList.另外,NacosServerList里面有方法getServers

private List<NacosServer> getServers() {
        try {
            String group = discoveryProperties.getGroup();
            List<Instance> instances = discoveryProperties.namingServiceInstance()
                    .selectInstances(serviceId, group, true);
            return instancesToServerList(instances);
        }
        catch (Exception e) {
            throw new IllegalStateException(
                    "Can not get service instances from nacos, serviceId=" + serviceId,
                    e);
        }
    }

selectInstances方法主要逻辑是向nacosserver发起http请求,获取服务的地址列表.