這篇文章將為大家詳細(xì)講解有關(guān)Spring Cloud Ribbon原理的示例分析，小編覺得挺實用的，因此分享給大家做個參考，希望大家閱讀完這篇文章后可以有所收獲。
簡介
Spring Cloud Ribbon 是一個基于Http和TCP的客服端負(fù)載均衡工具，它是基于Netflix Ribbon實現(xiàn)的。它不像服務(wù)注冊中心、配置中心、API網(wǎng)關(guān)那樣獨立部署，但是它幾乎存在于每個微服務(wù)的基礎(chǔ)設(shè)施中。包括前面的提供的聲明式服務(wù)調(diào)用也是基于該Ribbon實現(xiàn)的。理解Ribbon對于我們使用Spring Cloud來講非常的重要，因為負(fù)載均衡是對系統(tǒng)的高可用、網(wǎng)絡(luò)壓力的緩解和處理能力擴容的重要手段之一。在上節(jié)的例子中，我們采用了聲明式的方式來實現(xiàn)負(fù)載均衡。實際上，內(nèi)部調(diào)用維護了一個RestTemplate對象，該對象會使用Ribbon的自動化配置，同時通過@LoadBalanced開啟客戶端負(fù)載均衡。其實RestTemplate是Spring自己提供的對象，不是新的內(nèi)容。讀者不知道RestTemplate可以查看相關(guān)的文檔。
現(xiàn)象
前兩天碰到一個ribbon相關(guān)的問題，覺得值得記錄一下。表象是對外的接口返回內(nèi)部異常，這個是封裝的統(tǒng)
一錯誤信息，Spring的異常處理器catch到未捕獲異常統(tǒng)一返回的信息。因此到日志平臺查看實際的異常:
org.springframework.web.client.HttpClientErrorException: 404 null
這里介紹一下背景，出現(xiàn)問題的開放網(wǎng)關(guān)，做點事情說白了就是轉(zhuǎn)發(fā)對應(yīng)的請求給后端的服務(wù)。這里用到了ribbon去做服務(wù)負(fù)載均衡、eureka負(fù)責(zé)服務(wù)發(fā)現(xiàn)。
這里出現(xiàn)404，首先看了下請求的url以及對應(yīng)的參數(shù)，都沒有發(fā)現(xiàn)問題，對應(yīng)的后端服務(wù)也沒有收到請求。這就比較詭異了，開始懷疑是ribbon或者Eureka的緩存導(dǎo)致請求到了錯誤的ip或端口，但由于日志中打印的是Eureka的serviceId而不是實際的ip:port，因此先加了個日志:
重慶分公司
重慶分公司
@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);
}
}這里是通過給RestTemplate添加攔截器的方式，但要注意，ribbon也是通過給RestTemplate添加攔截器實現(xiàn)的解析serviceId到實際的ip:port，因此需要注意下優(yōu)先級添加到ribbon的 LoadBalancerInterceptor 之后，我這里是通過Spring的初始化完成事件的回調(diào)中添加的，另外也添加了另一條日志，在catch到這個異常的時候，利用Eureka的 DiscoveryClient#getInstances 獲取到當(dāng)前的實例信息。
之后在測試環(huán)境中復(fù)現(xiàn)了這個問題，看了下日志，eurek中緩存的實例信息是對的，但是實際調(diào)用的確實另外一個服務(wù)的地址，從而導(dǎo)致了接口404。
源碼解析
從上述的信息中可以知道，問題出在ribbon中，具體的原因后面會說，這里先講一下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 {
}注意這個注解 @RibbonClients , 如果想要覆蓋Spring Cloud提供的默認(rèn)Ribbon配置就可以使用這個注解，最終的解析類是:
public class RibbonClientConfigurationRegistrar implements ImportBeanDefinitionRegistrar {
@Override
public void registerBeanDefinitions(AnnotationMetadata metadata,
BeanDefinitionRegistry registry) {
Map 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 client = metadata.getAnnotationAttributes(
RibbonClient.class.getName(), true);
String name = getClientName(client);
if (name != null) {
registerClientConfiguration(registry, name, client.get("configuration"));
}
}
private String getClientName(Map 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，因此會注冊RibbonClientSpecification類型的bean,注意名稱以 default. 開頭，類型是RibbonAutoConfiguration,注意上面說的RibbonAutoConfiguration被@RibbonClients修飾。
然后再回到上面的源碼:
public class RibbonAutoConfiguration {
//上文中會解析被@RibbonClients注解修飾的類，然后注冊類型為RibbonClientSpecification的bean。
//主要有兩個: RibbonAutoConfiguration、RibbonEurekaAutoConfiguration
@Autowired(required = false)
private List configurations = new ArrayList<>();
@Bean
public SpringClientFactory springClientFactory() {
//初始化SpringClientFactory,并將上面的配置注入進去，這段很重要。
SpringClientFactory factory = new SpringClientFactory();
factory.setConfigurations(this.configurations);
return factory;
}
//其他的都是提供一些默認(rèn)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 {}
}
} 注意這里的SpringClientFactory, ribbon默認(rèn)情況下，每個eureka的serviceId(服務(wù))，都會分配自己獨立的Spring的上下文,即ApplicationContext, 然后這個上下文中包含了必要的一些bean,比如: ILoadBalancer 、 ServerListFilter 等。而Spring Cloud默認(rèn)是使用RestTemplate封裝了ribbon的調(diào)用，核心是通過一個攔截器:
@Bean
@ConditionalOnMissingBean
public RestTemplateCustomizer restTemplateCustomizer(
final LoadBalancerInterceptor loadBalancerInterceptor) {
return new RestTemplateCustomizer() {
@Override
public void customize(RestTemplate restTemplate) {
List list = new ArrayList<>(
restTemplate.getInterceptors());
list.add(loadBalancerInterceptor);
restTemplate.setInterceptors(list);
}
};
} 因此核心是通過這個攔截器實現(xiàn)的負(fù)載均衡:
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(); //這里傳入的url是解析之前的，即http://serviceId/服務(wù)地址的形式
String serviceName = originalUri.getHost(); //解析拿到對應(yīng)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));
}
}然后將請求轉(zhuǎn)發(fā)給LoadBalancerClient:
public class RibbonLoadBalancerClient implements LoadBalancerClient {
@Override
public T execute(String serviceId, LoadBalancerRequest request) throws IOException {
ILoadBalancer loadBalancer = getLoadBalancer(serviceId); //獲取對應(yīng)的LoadBalancer
Server server = getServer(loadBalancer); //獲取服務(wù)器，這里會執(zhí)行對應(yīng)的分流策略，比如輪訓(xùn)
//、隨機等
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);
}
} 而這里的LoadBalancer是通過上文中提到的SpringClientFactory獲取到的，這里會初始化一個新的Spring上下文，然后將Ribbon默認(rèn)的配置類，比如說: RibbonAutoConfiguration 、 RibbonEurekaAutoConfiguration 等添加進去, 然后將當(dāng)前spring的上下文設(shè)置為parent，再調(diào)用refresh方法進行初始化。
