Spring Cloud Feign重试机制

Spring Cloud Feign重试机制

Feign组件默认使用Ribbon的重试机制并增长了根据状态码判断重试机制，默认状况下是不启用的。Feign使用的是Spring Retry组件，须要引入依赖才能启用。

一、POM引入Spring Retry

<dependency>
        <groupId>org.springframework.retry</groupId>
        <artifactId>spring-retry</artifactId>
  </dependency>

二、配置文件

eureka-client:
   ribbon:
      MaxAutoRetries: 1
      MaxAutoRetriesNextServer: 1
      retryableStatusCodes: 500,404 
      OkToRetryOnAllOperations: true 
      NFLoadBalancerRuleClassName: com.netflix.loadbalancer.AvailabilityFilteringRule #负载均衡规则

eureka-client 是本身的serverId，MaxAutoRetries同一台服务器上的最大重试次数（不包括第一次尝试），MaxAutoRetriesNextServer要重试的下一个服务器的最大数量（不包括第一个服务器），retryableStatusCodes能够根据接口返回的状态码判断是否重试其余服务，OkToRetryOnAllOperations只对全部的超时请求重试

注意： Ribbon的重试机制只有对GET请求或者设置了OkToRetryOnAllOperations生效 详情请查看源码：

public class RibbonLoadBalancedRetryPolicy implements LoadBalancedRetryPolicy {
...
	public boolean canRetry(LoadBalancedRetryContext context) {
		HttpMethod method = context.getRequest().getMethod();
		return HttpMethod.GET == method || lbContext.isOkToRetryOnAllOperations();
	}
...
}

Feign对返回状态码作了重试判断RetryableFeignLoadBalancer

public class RetryableFeignLoadBalancer extends FeignLoadBalancer
	implements ServiceInstanceChooser {
	...
	[@Override](https://my.oschina.net/u/1162528)
	public RibbonResponse execute(final RibbonRequest request,
			IClientConfig configOverride) throws IOException {
	...
		if (retryPolicy != null
						&& retryPolicy.retryableStatusCode(response.status())) {
					byte[] byteArray = response.body() == null ? new byte[] {}
							: StreamUtils
									.copyToByteArray(response.body().asInputStream());
					response.close();
					throw new RibbonResponseStatusCodeException(
							RetryableFeignLoadBalancer.this.clientName, response,
							byteArray, request.getUri());
		}
	...
	}
	...
}

重试机制用的是Spring Retry组件当抛出异常时进行重试！

GET请求指的是feign client 请求其余client时声明的那个interface中mapping注解类型，RequestMapping不设置method默认为GET请求

@FeignClient("stores")
public interface StoreClient {
    @RequestMapping(method = RequestMethod.GET, value = "/stores")
    List<Store> getStores();

    @RequestMapping(method = RequestMethod.POST, value = "/stores/{storeId}", consumes = "application/json")
    Store update(@PathVariable("storeId") Long storeId, Store store);
}