声明:代码不是我写的=_=

现象

前两天碰到一个ribbon相关的问题，觉得值得简单记录一下。表象是对外的接口返回内部异常，这个是封装的统一错误信息，Spring的异常处理器catch到未捕获异常统一返回的信息。因此到日志平台查看实际的异常:

org.springframework.web.client.HttpClientErrorException: 404 null

这里介绍一下背景，出现问题的开放网关，做点事情说白了就是转发对应的请求给后端的服务。这里用到了ribbon去做服务负载均衡、eureka负责服务发现。这里出现404，首先看了下请求的url以及对应的参数，都没有发现问题，对应的后端服务也没有收到请求。这就比较诡异了，开始怀疑是ribbon或者Eureka的缓存导致请求到了错误的ip或端口，但由于日志中打印的是Eureka的serviceId而不是实际的ip:port，因此先加了个日志:

@Slf4j
public class CustomHttpRequestInterceptor implements ClientHttpRequestInterceptor {

    @Override
    public ClientHttpResponse intercept(HttpRequest request, byte[] body, ClientHttpRequestExecution execution) throws IOException {
        log.info("Request , url:{},method:{}.", request.getURI(), request.getMethod());
        return execution.execute(request, body);
    }
}

这里是通过给RestTemplate添加拦截器的方式，但要注意，ribbon也是通过给RestTemplate添加拦截器实现的解析serviceId到实际的ip:port，因此需要注意下优先级添加到ribbon的LoadBalancerInterceptor之后，我这里是通过Spring的初始化完成事件的回调中添加的，另外也添加了另一条日志，在catch到这个异常的时候，利用Eureka的DiscoveryClient#getInstances获取到当前的实例信息。
之后在测试环境中复现了这个问题，看了下日志，eurek中缓存的实例信息是对的，但是实际调用的确实另外一个服务的地址，从而导致了接口404。

源码解析

从上述的信息中可以知道，问题出在ribbon中，具体的原因后面会说，这里先讲一下Spring Cloud Ribbon的初始化流程。

@Configuration
@ConditionalOnClass({ IClient.class, RestTemplate.class, AsyncRestTemplate.class, Ribbon.class})
@RibbonClients
@AutoConfigureAfter(name = "org.springframework.cloud.netflix.eureka.EurekaClientAutoConfiguration")
@AutoConfigureBefore({LoadBalancerAutoConfiguration.class, AsyncLoadBalancerAutoConfiguration.class})
@EnableConfigurationProperties({RibbonEagerLoadProperties.class, ServerIntrospectorProperties.class})
public class RibbonAutoConfiguration {
}

注意这个注解@RibbonClients, 如果想要覆盖Spring Cloud提供的默认Ribbon配置就可以使用这个注解，最终的解析类是:

public class RibbonClientConfigurationRegistrar implements ImportBeanDefinitionRegistrar {

  @Override
  public void registerBeanDefinitions(AnnotationMetadata metadata,
      BeanDefinitionRegistry registry) {
    Map<String, Object> attrs = metadata.getAnnotationAttributes(
        RibbonClients.class.getName(), true);
    if (attrs != null && attrs.containsKey("value")) {
      AnnotationAttributes[] clients = (AnnotationAttributes[]) attrs.get("value");
      for (AnnotationAttributes client : clients) {
        registerClientConfiguration(registry, getClientName(client),
            client.get("configuration"));
      }
    }
    if (attrs != null && attrs.containsKey("defaultConfiguration")) {
      String name;
      if (metadata.hasEnclosingClass()) {
        name = "default." + metadata.getEnclosingClassName();
      } else {
        name = "default." + metadata.getClassName();
      }
      registerClientConfiguration(registry, name,
          attrs.get("defaultConfiguration"));
    }
    Map<String, Object> client = metadata.getAnnotationAttributes(
        RibbonClient.class.getName(), true);
    String name = getClientName(client);
    if (name != null) {
      registerClientConfiguration(registry, name, client.get("configuration"));
    }
  }

  private String getClientName(Map<String, Object> client) {
    if (client == null) {
      return null;
    }
    String value = (String) client.get("value");
    if (!StringUtils.hasText(value)) {
      value = (String) client.get("name");
    }
    if (StringUtils.hasText(value)) {
      return value;
    }
    throw new IllegalStateException(
        "Either 'name' or 'value' must be provided in @RibbonClient");
  }

  private void registerClientConfiguration(BeanDefinitionRegistry registry,
      Object name, Object configuration) {
    BeanDefinitionBuilder builder = BeanDefinitionBuilder
        .genericBeanDefinition(RibbonClientSpecification.class);
    builder.addConstructorArgValue(name);
    builder.addConstructorArgValue(configuration);
    registry.registerBeanDefinition(name + ".RibbonClientSpecification",
        builder.getBeanDefinition());
  }
}

atrrs包含defaultConfiguration，因此会注册RibbonClientSpecification类型的bean,注意名称以default.开头，类型是RibbonAutoConfiguration,注意上面说的RibbonAutoConfiguration被@RibbonClients修饰。
然后再回到上面的源码:

public class RibbonAutoConfiguration {
       

        //上文中会解析被@RibbonClients注解修饰的类，然后注册类型为RibbonClientSpecification的bean。
        //主要有两个: RibbonAutoConfiguration、RibbonEurekaAutoConfiguration
  @Autowired(required = false)
  private List<RibbonClientSpecification> configurations = new ArrayList<>();
      
  @Bean
  public SpringClientFactory springClientFactory() {
                //初始化SpringClientFactory,并将上面的配置注入进去，这段很重要。
    SpringClientFactory factory = new SpringClientFactory();
    factory.setConfigurations(this.configurations);
    return factory;
  }
         //其他的都是提供一些默认的bean配置

  @Bean
  @ConditionalOnMissingBean(LoadBalancerClient.class)
  public LoadBalancerClient loadBalancerClient() {
    return new RibbonLoadBalancerClient(springClientFactory());
  }

  @Bean
  @ConditionalOnClass(name = "org.springframework.retry.support.RetryTemplate")
  @ConditionalOnMissingBean
  public LoadBalancedRetryPolicyFactory loadBalancedRetryPolicyFactory(SpringClientFactory clientFactory) {
    return new RibbonLoadBalancedRetryPolicyFactory(clientFactory);
  }

  @Bean
  @ConditionalOnMissingClass(value = "org.springframework.retry.support.RetryTemplate")
  @ConditionalOnMissingBean
  public LoadBalancedRetryPolicyFactory neverRetryPolicyFactory() {
    return new LoadBalancedRetryPolicyFactory.NeverRetryFactory();
  }

  @Bean
  @ConditionalOnClass(name = "org.springframework.retry.support.RetryTemplate")
  @ConditionalOnMissingBean
  public LoadBalancedBackOffPolicyFactory loadBalancedBackoffPolicyFactory() {
    return new LoadBalancedBackOffPolicyFactory.NoBackOffPolicyFactory();
  }

  @Bean
  @ConditionalOnClass(name = "org.springframework.retry.support.RetryTemplate")
  @ConditionalOnMissingBean
  public LoadBalancedRetryListenerFactory loadBalancedRetryListenerFactory() {
    return new LoadBalancedRetryListenerFactory.DefaultRetryListenerFactory();
  }

  @Bean
  @ConditionalOnMissingBean
  public PropertiesFactory propertiesFactory() {
    return new PropertiesFactory();
  }
  
  @Bean
  @ConditionalOnProperty(value = "ribbon.eager-load.enabled", matchIfMissing = false)
  public RibbonApplicationContextInitializer ribbonApplicationContextInitializer() {
    return new RibbonApplicationContextInitializer(springClientFactory(),
        ribbonEagerLoadProperties.getClients());
  }

  @Configuration
  @ConditionalOnClass(HttpRequest.class)
  @ConditionalOnRibbonRestClient
  protected static class RibbonClientConfig {

    @Autowired
    private SpringClientFactory springClientFactory;

    @Bean
    public RestTemplateCustomizer restTemplateCustomizer(
        final RibbonClientHttpRequestFactory ribbonClientHttpRequestFactory) {
      return new RestTemplateCustomizer() {
        @Override
        public void customize(RestTemplate restTemplate) {
          restTemplate.setRequestFactory(ribbonClientHttpRequestFactory);
        }
      };
    }

    @Bean
    public RibbonClientHttpRequestFactory ribbonClientHttpRequestFactory() {
      return new RibbonClientHttpRequestFactory(this.springClientFactory);
    }
  }

  //TODO: support for autoconfiguring restemplate to use apache http client or okhttp

  @Target({ ElementType.TYPE, ElementType.METHOD })
  @Retention(RetentionPolicy.RUNTIME)
  @Documented
  @Conditional(OnRibbonRestClientCondition.class)
  @interface ConditionalOnRibbonRestClient { }

  private static class OnRibbonRestClientCondition extends AnyNestedCondition {
    public OnRibbonRestClientCondition() {
      super(ConfigurationPhase.REGISTER_BEAN);
    }

    @Deprecated //remove in Edgware"
    @ConditionalOnProperty("ribbon.http.client.enabled")
    static class ZuulProperty {}

    @ConditionalOnProperty("ribbon.restclient.enabled")
    static class RibbonProperty {}
  }
}

注意这里的SpringClientFactory, ribbon默认情况下，每个eureka的serviceId(服务)，都会分配自己独立的Spring的上下文,即ApplicationContext, 然后这个上下文中包含了必要的一些bean,比如: ILoadBalancer 、ServerListFilter 等。而Spring Cloud默认是使用RestTemplate封装了ribbon的调用，核心是通过一个拦截器:

@Bean
    @ConditionalOnMissingBean
    public RestTemplateCustomizer restTemplateCustomizer(
        final LoadBalancerInterceptor loadBalancerInterceptor) {
      return new RestTemplateCustomizer() {
        @Override
        public void customize(RestTemplate restTemplate) {
          List<ClientHttpRequestInterceptor> list = new ArrayList<>(
              restTemplate.getInterceptors());
          list.add(loadBalancerInterceptor);
          restTemplate.setInterceptors(list);
        }
      };
    }

因此核心是通过这个拦截器实现的负载均衡:

public class LoadBalancerInterceptor implements ClientHttpRequestInterceptor {

  private LoadBalancerClient loadBalancer;
  private LoadBalancerRequestFactory requestFactory;

  @Override
  public ClientHttpResponse intercept(final HttpRequest request, final byte[] body,
      final ClientHttpRequestExecution execution) throws IOException {
    final URI originalUri = request.getURI(); //这里传入的url是解析之前的，即http://serviceId/服务地址的形式
    String serviceName = originalUri.getHost(); //解析拿到对应的serviceId
    Assert.state(serviceName != null, "Request URI does not contain a valid hostname: " + originalUri);
    return this.loadBalancer.execute(serviceName, requestFactory.createRequest(request, body, execution));
  }
}

然后将请求转发给LoadBalancerClient:

public class RibbonLoadBalancerClient implements LoadBalancerClient {
@Override
  public <T> T execute(String serviceId, LoadBalancerRequest<T> request) throws IOException {
    ILoadBalancer loadBalancer = getLoadBalancer(serviceId); //获取对应的LoadBalancer
    Server server = getServer(loadBalancer); //获取服务器，这里会执行对应的分流策略，比如轮训
                //、随机等
    if (server == null) {
      throw new IllegalStateException("No instances available for " + serviceId);
    }
    RibbonServer ribbonServer = new RibbonServer(serviceId, server, isSecure(server,
        serviceId), serverIntrospector(serviceId).getMetadata(server));

    return execute(serviceId, ribbonServer, request);
  }
}

而这里的LoadBalancer是通过上文中提到的SpringClientFactory获取到的，这里会初始化一个新的Spring上下文，然后将Ribbon默认的配置类，比如说:RibbonAutoConfiguration、RibbonEurekaAutoConfiguration等添加进去, 然后将当前spring的上下文设置为parent，再调用refresh方法进行初始化。

public class SpringClientFactory extends NamedContextFactory<RibbonClientSpecification> {
  protected AnnotationConfigApplicationContext createContext(String name) {
    AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
    if (this.configurations.containsKey(name)) {
      for (Class<?> configuration : this.configurations.get(name)
          .getConfiguration()) {
        context.register(configuration);
      }
    }
    for (Map.Entry<String, C> entry : this.configurations.entrySet()) {
      if (entry.getKey().startsWith("default.")) {
        for (Class<?> configuration : entry.getValue().getConfiguration()) {
          context.register(configuration);
        }
      }
    }
    context.register(PropertyPlaceholderAutoConfiguration.class,
        this.defaultConfigType);
    context.getEnvironment().getPropertySources().addFirst(new MapPropertySource(
        this.propertySourceName,
        Collections.<String, Object> singletonMap(this.propertyName, name)));
    if (this.parent != null) {
      // Uses Environment from parent as well as beans
      context.setParent(this.parent);
    }
    context.refresh();
    return context;
  }
}

最核心的就在这一段，也就是说对于每一个不同的serviceId来说，都拥有一个独立的spring上下文，并且在第一次调用这个服务的时候，会初始化ribbon相关的所有bean，如果不存在才回去父context中去找。

再回到上文中根据分流策略获取实际的ip:port的代码段:

public class RibbonLoadBalancerClient implements LoadBalancerClient {
@Override
  public <T> T execute(String serviceId, LoadBalancerRequest<T> request) throws IOException {
    ILoadBalancer loadBalancer = getLoadBalancer(serviceId); //获取对应的LoadBalancer
    Server server = getServer(loadBalancer); //获取服务器，这里会执行对应的分流策略，比如轮训
                //、随机等
    if (server == null) {
      throw new IllegalStateException("No instances available for " + serviceId);
    }
    RibbonServer ribbonServer = new RibbonServer(serviceId, server, isSecure(server,
        serviceId), serverIntrospector(serviceId).getMetadata(server));

    return execute(serviceId, ribbonServer, request);
  }
}

  protected Server getServer(ILoadBalancer loadBalancer) {
    if (loadBalancer == null) {
      return null;
    }
                // 选择对应的服务器
    return loadBalancer.chooseServer("default"); // TODO: better handling of key
  }

public class ZoneAwareLoadBalancer<T extends Server> extends DynamicServerListLoadBalancer<T> {
@Override
    public Server chooseServer(Object key) {
        if (!ENABLED.get() || getLoadBalancerStats().getAvailableZones().size() <= 1) {
            logger.debug("Zone aware logic disabled or there is only one zone");
            return super.chooseServer(key); //默认不配置可用区，走的是这段
        }
        Server server = null;
        try {
            LoadBalancerStats lbStats = getLoadBalancerStats();
            Map<String, ZoneSnapshot> zoneSnapshot = ZoneAvoidanceRule.createSnapshot(lbStats);
            logger.debug("Zone snapshots: {}", zoneSnapshot);
            if (triggeringLoad == null) {
                triggeringLoad = DynamicPropertyFactory.getInstance().getDoubleProperty(
                        "ZoneAwareNIWSDiscoveryLoadBalancer." + this.getName() + ".triggeringLoadPerServerThreshold", 0.2d);
            }

            if (triggeringBlackoutPercentage == null) {
                triggeringBlackoutPercentage = DynamicPropertyFactory.getInstance().getDoubleProperty(
                        "ZoneAwareNIWSDiscoveryLoadBalancer." + this.getName() + ".avoidZoneWithBlackoutPercetage", 0.99999d);
            }
            Set<String> availableZones = ZoneAvoidanceRule.getAvailableZones(zoneSnapshot, triggeringLoad.get(), triggeringBlackoutPercentage.get());
            logger.debug("Available zones: {}", availableZones);
            if (availableZones != null &&  availableZones.size() < zoneSnapshot.keySet().size()) {
                String zone = ZoneAvoidanceRule.randomChooseZone(zoneSnapshot, availableZones);
                logger.debug("Zone chosen: {}", zone);
                if (zone != null) {
                    BaseLoadBalancer zoneLoadBalancer = getLoadBalancer(zone);
                    server = zoneLoadBalancer.chooseServer(key);
                }
            }
        } catch (Exception e) {
            logger.error("Error choosing server using zone aware logic for load balancer={}", name, e);
        }
        if (server != null) {
            return server;
        } else {
            logger.debug("Zone avoidance logic is not invoked.");
            return super.chooseServer(key);
        }
    }

    //实际走到的方法
    public Server chooseServer(Object key) {
        if (counter == null) {
            counter = createCounter();
        }
        counter.increment();
        if (rule == null) {
            return null;
        } else {
            try {
                return rule.choose(key);
            } catch (Exception e) {
                logger.warn("LoadBalancer [{}]:  Error choosing server for key {}", name, key, e);
                return null;
            }
        }
    }
}

也就是说最终会调用IRule选择到一个节点，这里支持很多策略，比如随机、轮训、响应时间权重等:

public interface IRule{

    public Server choose(Object key);
    
    public void setLoadBalancer(ILoadBalancer lb);
    
    public ILoadBalancer getLoadBalancer();    
}

这里的LoadBalancer是在BaseLoadBalancer的构造器中设置的，上文说过，对于每一个serviceId服务来说，当第一次调用的时候会初始化对应的spring上下文，而这个上下文中包含了所有ribbon相关的bean，其中就包括ILoadBalancer、IRule。

原因

通过跟踪堆栈，发现不同的serviceId，IRule是同一个, 而上文说过，每个serviceId都拥有自己独立的上下文,包括独立的loadBalancer、IRule，而IRule是同一个，因此怀疑是这个bean是通过parent context获取到的，换句话说应用自己定义了一个这样的bean。查看代码果然如此。这样就会导致一个问题，IRule是共享的，而其他bean是隔离开的，因此后面的serviceId初始化的时候，会修改这个IRule的LoadBalancer, 导致之前的服务获取到的实例信息是错误的，从而导致接口404。

public class BaseLoadBalancer extends AbstractLoadBalancer implements
        PrimeConnections.PrimeConnectionListener, IClientConfigAware {
    public BaseLoadBalancer() {
        this.name = DEFAULT_NAME;
        this.ping = null;
        setRule(DEFAULT_RULE);  // 这里会设置IRule的loadbalancer
        setupPingTask();
        lbStats = new LoadBalancerStats(DEFAULT_NAME);
    }
}

解决方案

解决方法也很简单，最简单就将这个自定义的IRule的bean干掉，另外更标准的做法是使用RibbonClients注解，具体做法可以参考文档。

总结

核心原因其实还是对于Spring Cloud的理解不够深刻，用法有错误，导致出现了一些比较诡异的问题。对于自己使用的组件、框架、甚至于每一个注解，都要了解其原理，能够清楚的说清楚这个注解有什么效果，有什么影响，而不是只着眼于解决眼前的问题。