ribbon配合restTemplate实现客户端负载均衡、超时重试

背景：
最近项目中要求实现请求转发的中间层，其中包含负载均衡和超时重试的功能。具体场景是：我们的服务作为客户端调用第三方服务，第三方服务提供了一个服务的IP和端口号的列表。我们需要根据不同的负载均衡算法来进行服务的调用。
实现方式：
在restTemplate,中使用注解@loadbalance,配合合理的ribbon的配置进行实现。
核心实现摘要：
restTemplate的bean

    @Bean
    @LoadBalanced
    public RestTemplate restTemplate() {
        return new RestTemplate();
    }

ribbon的配置

peer-coupon: #服务的ID
    ribbon:
      listOfServers: 10.10.11.10:7221,12.92.11.36:6221 # 节点列表
      ReadTimeout: 300 # 读超时时间
      ConnectTimeout: 500 # 连接超时时间
      MaxAutoRetries: 1 # 访问当前的节点重试次数，例如选择了节点A ，A访问不通，则重试一次。
      MaxAutoRetriesNextServer: 2 #当重试完当前节点之后，选择下一个节点的次数。
      OkToRetryOnAllOperations: true # 所有的请求都失败重试
      #NFLoadBalancerRuleClassName: com.netflix.loadbalancer.WeightedResponseTimeRule
      #NFLoadBalancerRuleClassName: com.netflix.loadbalancer.RoundRobinRule
      NFLoadBalancerRuleClassName: com.netflix.loadbalancer.RandomRule
      # 其他负载均衡算法，参考相应包下的类。
      #NFLoadBalancerRuleClassName: com.umpay.uchains.proxy.loadbalance.rule.IpHashRule #这是自己实现的负载均衡算法
      NFLoadBalancerClassName: com.netflix.loadbalancer.ZoneAwareLoadBalancer #这是负载均衡的一个控制器。
spring:
    cloud:
      loadbalancer:
        retry:
          enabled: true  #这个配置项 配置了 支持重试

核心代码

        String url = "http://"+serviceId+uri;  //serviceId 对应的是配置文件中的 服务的ID 也就是 例子中的 peer-coupon
        logger.debug("post={}, json={}",url,object);
        return restTemplate.postForObject(url,object,JSONObject.class);

原理分析：

１、restTemplate继承了 InterceptingHttpAccessor

public class RestTemplate extends InterceptingHttpAccessor implements RestOperations

２、InterceptingHttpAccessor 内部持有拦截器的列表

public abstract class InterceptingHttpAccessor extends HttpAccessor {

	private final List<ClientHttpRequestInterceptor> interceptors = new ArrayList<>();

３、类LoadBalancerAutoConfiguration 实现了对 restTemplate中拦截器的加载。
内部静态类 LoadBalancerInterceptorConfig 首先生成LoadBalancerInterceptor 再往restTemplate内添加拦截器。
LoadBalancerInterceptorConfig 的生成依赖于 LoadBalancerRequestFactory 和 LoadBalancerClient　。
LoadBalancerRequestFactory由LoadBalancerClient和transformers构造完成。
LoadBalancerClient依赖于注解@ConditionalOnBean(LoadBalancerClient.class)。
另外该类的配置中还支持　RetryInterceptorAutoConfiguration具有重试能力的拦截器配置。

@Configuration
@ConditionalOnClass(RestTemplate.class)
@ConditionalOnBean(LoadBalancerClient.class)
@EnableConfigurationProperties(LoadBalancerRetryProperties.class)
public class LoadBalancerAutoConfiguration {

	@LoadBalanced
	@Autowired(required = false)
	private List<RestTemplate> restTemplates = Collections.emptyList();

	@Bean
	public SmartInitializingSingleton loadBalancedRestTemplateInitializerDeprecated(
			final ObjectProvider<List<RestTemplateCustomizer>> restTemplateCustomizers) {
		return () -> restTemplateCustomizers.ifAvailable(customizers -> {
            for (RestTemplate restTemplate : LoadBalancerAutoConfiguration.this.restTemplates) {
                for (RestTemplateCustomizer customizer : customizers) {
                    customizer.customize(restTemplate);
                }
            }
        });
	}

	@Autowired(required = false)
	private List<LoadBalancerRequestTransformer> transformers = Collections.emptyList();

	@Bean
	@ConditionalOnMissingBean
	public LoadBalancerRequestFactory loadBalancerRequestFactory(
			LoadBalancerClient loadBalancerClient) {
		return new LoadBalancerRequestFactory(loadBalancerClient, transformers);
	}

	@Configuration
	@ConditionalOnMissingClass("org.springframework.retry.support.RetryTemplate")
	static class LoadBalancerInterceptorConfig {
		@Bean
		public LoadBalancerInterceptor ribbonInterceptor(
				LoadBalancerClient loadBalancerClient,
				LoadBalancerRequestFactory requestFactory) {
			return new LoadBalancerInterceptor(loadBalancerClient, requestFactory);
		}

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

	@Configuration
	@ConditionalOnClass(RetryTemplate.class)
	public static class RetryAutoConfiguration {

		@Bean
		@ConditionalOnMissingBean
		public LoadBalancedRetryFactory loadBalancedRetryFactory() {
			return new LoadBalancedRetryFactory() {};
		}
	}

	@Configuration
	@ConditionalOnClass(RetryTemplate.class)
	public static class RetryInterceptorAutoConfiguration {
		@Bean
		@ConditionalOnMissingBean
		public RetryLoadBalancerInterceptor ribbonInterceptor(
				LoadBalancerClient loadBalancerClient, LoadBalancerRetryProperties properties,
				LoadBalancerRequestFactory requestFactory,
				LoadBalancedRetryFactory loadBalancedRetryFactory) {
			return new RetryLoadBalancerInterceptor(loadBalancerClient, properties,
					requestFactory, loadBalancedRetryFactory);
		}

		@Bean
		@ConditionalOnMissingBean
		public RestTemplateCustomizer restTemplateCustomizer(
				final RetryLoadBalancerInterceptor loadBalancerInterceptor) {
			return restTemplate -> {
                List<ClientHttpRequestInterceptor> list = new ArrayList<>(
                        restTemplate.getInterceptors());
                list.add(loadBalancerInterceptor);
                restTemplate.setInterceptors(list);
            };
		}
	}
}

４、具体的LoadBalancerClient是如何生成的？　
参考类RibbonClientConfiguration。
生成的LoadBalancerClient　被封装在　RibbonLoadBalancerContext　内部。

@SuppressWarnings("deprecation")
@Configuration
@EnableConfigurationProperties
//Order is important here, last should be the default, first should be optional
// see https://github.com/spring-cloud/spring-cloud-netflix/issues/2086#issuecomment-316281653
@Import({HttpClientConfiguration.class, OkHttpRibbonConfiguration.class, RestClientRibbonConfiguration.class, HttpClientRibbonConfiguration.class})
public class RibbonClientConfiguration {

	public static final int DEFAULT_CONNECT_TIMEOUT = 1000;
	public static final int DEFAULT_READ_TIMEOUT = 1000;

	@RibbonClientName
	private String name = "client";

	// TODO: maybe re-instate autowired load balancers: identified by name they could be
	// associated with ribbon clients

	@Autowired
	private PropertiesFactory propertiesFactory;

	@Bean
	@ConditionalOnMissingBean
	public IClientConfig ribbonClientConfig() {
		DefaultClientConfigImpl config = new DefaultClientConfigImpl();
		config.loadProperties(this.name);
		config.set(CommonClientConfigKey.ConnectTimeout, DEFAULT_CONNECT_TIMEOUT);
		config.set(CommonClientConfigKey.ReadTimeout, DEFAULT_READ_TIMEOUT);
		return config;
	}

	@Bean
	@ConditionalOnMissingBean
	public IRule ribbonRule(IClientConfig config) {
		if (this.propertiesFactory.isSet(IRule.class, name)) {
			return this.propertiesFactory.get(IRule.class, config, name);
		}
		ZoneAvoidanceRule rule = new ZoneAvoidanceRule();
		rule.initWithNiwsConfig(config);
		return rule;
	}

	@Bean
	@ConditionalOnMissingBean
	public IPing ribbonPing(IClientConfig config) {
		if (this.propertiesFactory.isSet(IPing.class, name)) {
			return this.propertiesFactory.get(IPing.class, config, name);
		}
		return new DummyPing();
	}

	@Bean
	@ConditionalOnMissingBean
	@SuppressWarnings("unchecked")
	public ServerList<Server> ribbonServerList(IClientConfig config) {
		if (this.propertiesFactory.isSet(ServerList.class, name)) {
			return this.propertiesFactory.get(ServerList.class, config, name);
		}
		ConfigurationBasedServerList serverList = new ConfigurationBasedServerList();
		serverList.initWithNiwsConfig(config);
		return serverList;
	}

	@Bean
	@ConditionalOnMissingBean
	public ServerListUpdater ribbonServerListUpdater(IClientConfig config) {
		return new PollingServerListUpdater(config);
	}

	@Bean
	@ConditionalOnMissingBean
	public ILoadBalancer ribbonLoadBalancer(IClientConfig config,
			ServerList<Server> serverList, ServerListFilter<Server> serverListFilter,
			IRule rule, IPing ping, ServerListUpdater serverListUpdater) {
		if (this.propertiesFactory.isSet(ILoadBalancer.class, name)) {
			return this.propertiesFactory.get(ILoadBalancer.class, config, name);
		}
		return new ZoneAwareLoadBalancer<>(config, rule, ping, serverList,
				serverListFilter, serverListUpdater);
	}

	@Bean
	@ConditionalOnMissingBean
	@SuppressWarnings("unchecked")
	public ServerListFilter<Server> ribbonServerListFilter(IClientConfig config) {
		if (this.propertiesFactory.isSet(ServerListFilter.class, name)) {
			return this.propertiesFactory.get(ServerListFilter.class, config, name);
		}
		ZonePreferenceServerListFilter filter = new ZonePreferenceServerListFilter();
		filter.initWithNiwsConfig(config);
		return filter;
	}

	@Bean
	@ConditionalOnMissingBean
	public RibbonLoadBalancerContext ribbonLoadBalancerContext(ILoadBalancer loadBalancer,
															   IClientConfig config, RetryHandler retryHandler) {
		return new RibbonLoadBalancerContext(loadBalancer, config, retryHandler);
	}

	@Bean
	@ConditionalOnMissingBean
	public RetryHandler retryHandler(IClientConfig config) {
		return new DefaultLoadBalancerRetryHandler(config);
	}

	@Bean
	@ConditionalOnMissingBean
	public ServerIntrospector serverIntrospector() {
		return new DefaultServerIntrospector();
	}

	@PostConstruct
	public void preprocess() {
		setRibbonProperty(name, DeploymentContextBasedVipAddresses.key(), name);
	}

	static class OverrideRestClient extends RestClient {

		private IClientConfig config;
		private ServerIntrospector serverIntrospector;

		protected OverrideRestClient(IClientConfig config,
				ServerIntrospector serverIntrospector) {
			super();
			this.config = config;
			this.serverIntrospector = serverIntrospector;
			initWithNiwsConfig(this.config);
		}

		@Override
		public URI reconstructURIWithServer(Server server, URI original) {
			URI uri = updateToSecureConnectionIfNeeded(original, this.config,
					this.serverIntrospector, server);
			return super.reconstructURIWithServer(server, uri);
		}

		@Override
		protected Client apacheHttpClientSpecificInitialization() {
			ApacheHttpClient4 apache = (ApacheHttpClient4) super.apacheHttpClientSpecificInitialization();
			apache.getClientHandler().getHttpClient().getParams().setParameter(
					ClientPNames.COOKIE_POLICY, CookiePolicy.IGNORE_COOKIES);
			return apache;
		}

	}

}

ribbon配合restTemplate实现客户端负载均衡、超时重试

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