聊聊spring cloud的LoadBalancerAutoConfiguration

序

本文主要研究一下spring cloud的LoadBalancerAutoConfiguration

RibbonAutoConfiguration

spring-cloud-netflix-ribbon-2.0.0.RC2-sources.jar!/org/springframework/cloud/netflix/ribbon/RibbonAutoConfiguration.java

@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);
            };
		}
	}
}

• 定義了LoadBalancerRequestFactory以及LoadBalancerInterceptorConfig、RetryAutoConfiguration、RetryInterceptorAutoConfiguration

LoadBalancerRetryProperties

spring-cloud-commons-2.0.0.RC2-sources.jar!/org/springframework/cloud/client/loadbalancer/LoadBalancerRetryProperties.java

/**
 * Configuration properties for the {@link LoadBalancerClient}.
 * @author Ryan Baxter
 */
@ConfigurationProperties("spring.cloud.loadbalancer.retry")
public class LoadBalancerRetryProperties {
    private boolean enabled = true;

    /**
     * Returns true if the load balancer should retry failed requests.
     * @return true if the load balancer should retry failed request, false otherwise.
     */
    public boolean isEnabled() {
        return enabled;
    }

    /**
     * Sets whether the load balancer should retry failed request.
     * @param enabled whether the load balancer should retry failed requests
     */
    public void setEnabled(boolean enabled) {
        this.enabled = enabled;
    }
}

• 這個配置是否開啓loadbalancer的retry

RetryLoadBalancerInterceptor

spring-cloud-commons-2.0.0.RC2-sources.jar!/org/springframework/cloud/client/loadbalancer/RetryLoadBalancerInterceptor.java

public class RetryLoadBalancerInterceptor implements ClientHttpRequestInterceptor {

	private LoadBalancerClient loadBalancer;
	private LoadBalancerRetryProperties lbProperties;
	private LoadBalancerRequestFactory requestFactory;
	private LoadBalancedRetryFactory lbRetryFactory;

	public RetryLoadBalancerInterceptor(LoadBalancerClient loadBalancer,
                                        LoadBalancerRetryProperties lbProperties,
                                        LoadBalancerRequestFactory requestFactory,
                                        LoadBalancedRetryFactory lbRetryFactory) {
        this.loadBalancer = loadBalancer;
        this.lbProperties = lbProperties;
        this.requestFactory = requestFactory;
        this.lbRetryFactory = lbRetryFactory;

    }

	@Override
	public ClientHttpResponse intercept(final HttpRequest request, final byte[] body,
										final ClientHttpRequestExecution execution) throws IOException {
		final URI originalUri = request.getURI();
		final String serviceName = originalUri.getHost();
		Assert.state(serviceName != null, "Request URI does not contain a valid hostname: " + originalUri);
		final LoadBalancedRetryPolicy retryPolicy = lbRetryFactory.createRetryPolicy(serviceName,
				loadBalancer);
		RetryTemplate template = createRetryTemplate(serviceName, request, retryPolicy);
		return template.execute(context -> {
			ServiceInstance serviceInstance = null;
			if (context instanceof LoadBalancedRetryContext) {
				LoadBalancedRetryContext lbContext = (LoadBalancedRetryContext) context;
				serviceInstance = lbContext.getServiceInstance();
			}
			if (serviceInstance == null) {
				serviceInstance = loadBalancer.choose(serviceName);
			}
			ClientHttpResponse response = RetryLoadBalancerInterceptor.this.loadBalancer.execute(
					serviceName, serviceInstance,
					requestFactory.createRequest(request, body, execution));
			int statusCode = response.getRawStatusCode();
			if (retryPolicy != null && retryPolicy.retryableStatusCode(statusCode)) {
				byte[] bodyCopy = StreamUtils.copyToByteArray(response.getBody());
				response.close();
				throw new ClientHttpResponseStatusCodeException(serviceName, response, bodyCopy);
			}
			return response;
		}, new LoadBalancedRecoveryCallback<ClientHttpResponse, ClientHttpResponse>() {
			//This is a special case, where both parameters to LoadBalancedRecoveryCallback are
			//the same.  In most cases they would be different.
			@Override
			protected ClientHttpResponse createResponse(ClientHttpResponse response, URI uri) {
				return response;
			}
		});
	}

	private RetryTemplate createRetryTemplate(String serviceName, HttpRequest request, LoadBalancedRetryPolicy retryPolicy) {
		RetryTemplate template = new RetryTemplate();
		BackOffPolicy backOffPolicy = lbRetryFactory.createBackOffPolicy(serviceName);
		template.setBackOffPolicy(backOffPolicy == null ? new NoBackOffPolicy() : backOffPolicy);
		template.setThrowLastExceptionOnExhausted(true);
		RetryListener[] retryListeners = lbRetryFactory.createRetryListeners(serviceName);
		if (retryListeners != null && retryListeners.length != 0) {
			template.setListeners(retryListeners);
		}
		template.setRetryPolicy(
				!lbProperties.isEnabled() || retryPolicy == null ? new NeverRetryPolicy()
						: new InterceptorRetryPolicy(request, retryPolicy, loadBalancer,
						serviceName));
		return template;
	}
}

• 實現了ClientHttpRequestInterceptor接口
• 經過lbRetryFactory.createRetryPolicy(serviceName,loadBalancer)建立重試策略，而後建立RetryTemplate

小結

LoadBalancerAutoConfiguration這個類定義了LoadBalancerRequestFactory以及LoadBalancerInterceptor，另外主要配置的是loadBalancer的重試。重試功能主要經過spring retry組件的RetryTemplate來實現。

doc

• Spring Cloud Finchley.RELEASE Documentation