SpringCloud @LoadBalanced 负载均衡原理

原创

用户3293499

发布于 2024-12-22 20:30:00

2420

LoadBalancerAutoConfiguration

代码里面一共有两个配置

一个是spring-cloud-common里面的org.springframework.cloud.client.loadbalancer.LoadBalancerAutoConfiguration；另外一个是 spring-cloud-loadbalancer里面的org.springframework.cloud.loadbalancer.config.LoadBalancerAutoConfiguration。

spring-cloud-common#LoadBalancerAutoConfiguration

spring-cloud-common正常是做规范用的，看package名称也能看出来，是配置客户端的,该类配置如下的bean:LoadBalancerRequestFactory,该bean用于创建请求，构造函数包含LoadBalancerClient,默认为BlockingLoadBalancerClient。另外，注册了拦截器，并获取到RestTemplate

public class LoadBalancerAutoConfiguration {

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

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

/**
 * 获取@LoadBalanced注解的RestTemplate
 */
@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);
            }
        }
    });
}

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

/**
 * 注册拦截器
 */
@Configuration(proxyBeanMethods = false)
@Conditional(RetryMissingOrDisabledCondition.class)
static class LoadBalancerInterceptorConfig {

    @Bean
    public LoadBalancerInterceptor loadBalancerInterceptor(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);
        };
    }

}

spring-cloud-loadbalancer里面的#LoadBalancerAutoConfiguration

该配置类注册了LoadBalancerZoneConfig和LoadBalancerClientFactory,后者继承了ReactiveLoadBalancer.Factory<ServiceInstance>。同时在@LoadBalancerClients中引入了LoadBalancerClientConfigurationRegistrar

LoadBalancerClientConfigurationRegistrar

用于加载配置

BlockingLoadBalancerClientAutoConfiguration

该配置类用于注册LoadBalancerClient

@Bean
@ConditionalOnBean(LoadBalancerClientFactory.class)
@ConditionalOnMissingBean
public LoadBalancerClient blockingLoadBalancerClient(LoadBalancerClientFactory loadBalancerClientFactory) {
    return new BlockingLoadBalancerClient(loadBalancerClientFactory);
}

ReactorLoadBalancerClientAutoConfiguration

改配置有几个条件，@ConditionalOnClass(WebClient.class),@ConditionalOnBean(ReactiveLoadBalancer.Factory.class,主要用于注册 ReactorLoadBalancerExchangeFilterFunction

LoadBalancerBeanPostProcessorAutoConfiguration

用于注册LoadBalancerWebClientBuilderBeanPostProcessor,DeferringLoadBalancerExchangeFilterFunction

LoadBalancerClientConfiguration

loadbalancer客户端配置，配置了默认的负载规则，默认为轮训，还支持随机的

@Bean
@ConditionalOnMissingBean
public ReactorLoadBalancer<ServiceInstance> reactorServiceInstanceLoadBalancer(Environment environment,
        LoadBalancerClientFactory loadBalancerClientFactory) {
    String name = environment.getProperty(LoadBalancerClientFactory.PROPERTY_NAME);
    return new RoundRobinLoadBalancer(
            loadBalancerClientFactory.getLazyProvider(name, ServiceInstanceListSupplier.class), name);
}

若引入了nacos,则nacos会默认调整为nacos的配置

NacosLoadBalancerClientConfiguration

@Bean
@ConditionalOnMissingBean
public ReactorLoadBalancer<ServiceInstance> nacosLoadBalancer(Environment environment,
        LoadBalancerClientFactory loadBalancerClientFactory,
        NacosDiscoveryProperties nacosDiscoveryProperties) {
    String name = environment.getProperty(LoadBalancerClientFactory.PROPERTY_NAME);
    return new NacosLoadBalancer(
            loadBalancerClientFactory.getLazyProvider(name,
                    ServiceInstanceListSupplier.class),
            name, nacosDiscoveryProperties);
}

nacos默认的机制为权重

ServiceInstance instance = NacosBalancer.getHostByRandomWeight3(instancesToChoose);

原理

首先获取到添加注解的RestTemplate,然后通过拦截器LoadBalancerInterceptor，进行请求拦截，并根据负责策略获取到最终的访问信息。

public class LoadBalancerInterceptor implements ClientHttpRequestInterceptor {

	private LoadBalancerClient loadBalancer;

	private LoadBalancerRequestFactory requestFactory;

	public LoadBalancerInterceptor(LoadBalancerClient loadBalancer, LoadBalancerRequestFactory requestFactory) {
		this.loadBalancer = loadBalancer;
		this.requestFactory = requestFactory;
	}

	public LoadBalancerInterceptor(LoadBalancerClient loadBalancer) {
		// for backwards compatibility
		this(loadBalancer, new LoadBalancerRequestFactory(loadBalancer));
	}

    /// 拦截
	@Override
	public ClientHttpResponse intercept(final HttpRequest request, final byte[] body,final ClientHttpRequestExecution execution) throws IOException {
		final URI originalUri = request.getURI();
		String serviceName = originalUri.getHost();
		Assert.state(serviceName != null, "Request URI does not contain a valid hostname: " + originalUri);
		return this.loadBalancer.execute(serviceName, this.requestFactory.createRequest(request, body, execution));
	}

}

增加了注解的resttemplate默认只能请求微服务的，此时想要支持IP+端口方式的，可以在LoadBalancerInterceptor前增加拦截器，可参考:Spring Cloud RestTemplate @LoadBalanced 支持ip、域名、服务名调用，注意修改优先级即可

原创声明：本文系作者授权腾讯云开发者社区发表，未经许可，不得转载。

如有侵权，请联系 cloudcommunity@tencent.com 删除。

load-balancing