Spring Cloud Ribbon的原理
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作者 | 郭慕荣
来源 | urlify.cn/fANvIr
直接开撸代码，通过代码来看Ribbon是如何实现的。
1：RibbonAutoConfiguration配置生成RibbonLoadBalancerClient实例。
代码位置：org.springframework.cloud.netflix.ribbon.RibbonAutoConfiguration
@Configuration
@Conditional({RibbonAutoConfiguration.RibbonClassesConditions.class})
@RibbonClients
@AutoConfigureAfter(
name = {"org.springframework.cloud.netflix.eureka.EurekaClientAutoConfiguration"}
)
@AutoConfigureBefore({LoadBalancerAutoConfiguration.class, AsyncLoadBalancerAutoConfiguration.class})
@EnableConfigurationProperties({RibbonEagerLoadProperties.class, ServerIntrospectorProperties.class})
public class RibbonAutoConfiguration {
@Autowired(
required = false
)
private List configurations = new ArrayList();
@Autowired
private RibbonEagerLoadProperties ribbonEagerLoadProperties;
//...略
@Bean
@ConditionalOnMissingBean({LoadBalancerClient.class})
public LoadBalancerClient loadBalancerClient() {
return new RibbonLoadBalancerClient(this.springClientFactory());
}
// ....略
}
先看配置条件项，RibbonAutoConfiguration配置必须在LoadBalancerAutoConfiguration配置前执行，因为在LoadBalancerAutoConfiguration配置中会使用RibbonLoadBalancerClient实例。
RibbonLoadBalancerClient继承自LoadBalancerClient接口，是负载均衡客户端，也是负载均衡策略的调用方。
2.LoadBalancerInterceptorConfig配置生成：
1).负载均衡拦截器LoadBalancerInterceptor实例
包含：
LoadBalancerClient实现类的RibbonLoadBalancerClient实例
负载均衡的请求创建工厂LoadBalancerRequestFactory:实例
2).RestTemplate自定义的RestTemplateCustomizer实例
代码位置：org.springframework.cloud.client.loadbalancer.LoadBalancerAutoConfiguration
@Configuration(proxyBeanMethods = false)
@ConditionalOnClass(RestTemplate.class)
@ConditionalOnBean(LoadBalancerClient.class)
@EnableConfigurationProperties(LoadBalancerRetryProperties.class)
public class LoadBalancerAutoConfiguration {
@LoadBalanced
@Autowired(required = false)
private List restTemplates = Collections.emptyList();
@Autowired(required = false)
private List transformers = Collections.emptyList();
@Bean
public SmartInitializingSingleton loadBalancedRestTemplateInitializerDeprecated(
final ObjectProvider> restTemplateCustomizers) {
return () -> restTemplateCustomizers.ifAvailable(customizers -> {
for (RestTemplate restTemplate : LoadBalancerAutoConfiguration.this.restTemplates) {
for (RestTemplateCustomizer customizer : customizers) {
customizer.customize(restTemplate);
}
}
});
}
@Bean
@ConditionalOnMissingBean
public LoadBalancerRequestFactory loadBalancerRequestFactory(
LoadBalancerClient loadBalancerClient) {
return new LoadBalancerRequestFactory(loadBalancerClient, this.transformers);
}
@Configuration(proxyBeanMethods = false)
@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 list = new ArrayList<>(
restTemplate.getInterceptors());
list.add(loadBalancerInterceptor);
restTemplate.setInterceptors(list);
};
}
}
// .....略
}
先看配置条件项：
要求在项目环境中必须要有RestTemplate类。
要求必须要有LoadBalancerClient接口的实现类的实例，也就是上一步生成的RibbonLoadBalancerClient。
3.通过上面一步创建的RestTemplateCustomizer配置所有RestTemplate实例，就是将负载均衡拦截器设置给RestTemplate实例。
@Configuration(proxyBeanMethods = false)
@ConditionalOnClass(RestTemplate.class)
@ConditionalOnBean(LoadBalancerClient.class)
@EnableConfigurationProperties(LoadBalancerRetryProperties.class)
public class LoadBalancerAutoConfiguration {
@LoadBalanced
@Autowired(required = false)
private List restTemplates = Collections.emptyList();
@Autowired(required = false)
private List transformers = Collections.emptyList();
@Bean
public SmartInitializingSingleton loadBalancedRestTemplateInitializerDeprecated(
final ObjectProvider> restTemplateCustomizers) {
return () -> restTemplateCustomizers.ifAvailable(customizers -> {
for (RestTemplate restTemplate : LoadBalancerAutoConfiguration.this.restTemplates) {
for (RestTemplateCustomizer customizer : customizers) {
customizer.customize(restTemplate);
}
}
});
}
@Bean
@ConditionalOnMissingBean
public LoadBalancerRequestFactory loadBalancerRequestFactory(
LoadBalancerClient loadBalancerClient) {
return new LoadBalancerRequestFactory(loadBalancerClient, this.transformers);
}
@Configuration(proxyBeanMethods = false)
@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 list = new ArrayList<>(
restTemplate.getInterceptors());
list.add(loadBalancerInterceptor);
restTemplate.setInterceptors(list);
};
}
}
// ...略
}
restTemplate.setInterceptors(list)这个地方就是注入负载均衡拦截器的地方LoadBalancerInterceptor。
从这个地方实际上也可以猜出来，RestTemplate可以通过注入的拦截器来构建相应的请求实现负载均衡。
也能看出来可以自定义拦截器实现其他目的。
4.RibbonClientConfiguration配置生成ZoneAwareLoadBalancer实例
代码位置：org.springframework.cloud.netflix.ribbon.RibbonClientConfiguration
@Configuration(proxyBeanMethods = false)
@EnableConfigurationProperties
@Import({ HttpClientConfiguration.class, OkHttpRibbonConfiguration.class,
RestClientRibbonConfiguration.class, HttpClientRibbonConfiguration.class })
public class RibbonClientConfiguration {
// ...略
@Bean
@ConditionalOnMissingBean
public ILoadBalancer ribbonLoadBalancer(IClientConfig config,
ServerList serverList, ServerListFilter 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);
}
// ...略
}
ZoneAwareLoadBalancer继承自ILoadBalancer接口，该接口有一个方法：
/**
* Choose a server from load balancer.
*
* @param key An object that the load balancer may use to determine which server to return. null if
* the load balancer does not use this parameter.
* @return server chosen
*/
public Server chooseServer(Object key);
ZoneAwareLoadBalancer就是一个具体的负载均衡实现类，也是默认的负载均衡类，通过对chooseServer方法的实现选取某个服务实例。
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