spring cloud zuul 配置全局回退无效的原因

1. 首先，spring cloud 的版本为 Edgware.SR3
2. 自定义FallbackProvider 的实现请点击这里，大神写的很详细；
3. 起初我的bootstrap.yml 配置服务路由为：

   routes:
       auth-server:
         strip-prefix: true
         sensitiveHeaders:
         path: /v1/auth-api/**
         url: http://localhost:8002/
       system-server:
         strip-prefix: true
         sensitiveHeaders:
         path: /v1/system-api/**
         url: http://localhost:8004/

4. 配置完MyServerFallbackProvider之后启动项目发现回退没生效，还是一直抛异常：com.netflix.zuul.exception.ZuulException:Connect to localhost:8004 [localhost/127.0.0.1, localhost/0:0:0:0:0:0:0:1] failed: Connection refused: connect
   at org.springframework.cloud.netflix.zuul.util.ZuulRuntimeException.(ZuulRuntimeException.java:33)
   at org.springframework.cloud.netflix.zuul.filters.route.SimpleHostRoutingFilter.run(SimpleHostRoutingFilter.java:207)
   at com.netflix.zuul.ZuulFilter.runFilter(ZuulFilter.java:112)
   at com.netflix.zuul.FilterProcessor.processZuulFilter(FilterProcessor.java:193)
   at com.netflix.zuul.FilterProcessor.runFilters(FilterProcessor.java:157)
   at com.netflix.zuul.FilterProcessor.route(FilterProcessor.java:118)
   at com.netflix.zuul.ZuulRunner.route(ZuulRunner.java:96)
5. 最终查看源码得知抛出异常而没有回退发现和zull 的默认 filter有关；对zuul 过滤器不了解的小伙伴点击这里，一下为zuul 的默认过滤器

   类型	顺序	过滤器	功能
   pre	-3	ServletDetectionFilter	标记处理Servlet的类型
   pre	-2	Servlet30WrapperFilter	包装HttpServletRequest请求
   pre	-1	FormBodyWrapperFilter	包装请求体
   route	1	DebugFilter	标记调试标志
   route	5	PreDecorationFilter	处理请求上下文供后续使用
   route	10	RibbonRoutingFilter	serviceId请求转发
   route	100	SimpleHostRoutingFilter	url请求转发
   route	500	SendForwardFilter	forward请求转发
   post	0	SendErrorFilter	处理有错误的请求响应
   post	1000	SendResponseFilter	处理正常的请求响应

   由于我的bootstrap.yml 路由配置为 url 形式（上文bootstrap.yml标红的部分） ，所以server 转发filter 为 SimpleHostRoutingFilter，最终通过hettpclient转发到服务端，而SimpleHostRoutingFilter的run()方法中直接抛出了ZuulRuntimeException:

   try {
      CloseableHttpResponse response = forward(this.httpClient, verb, uri, request,
            headers, params, requestEntity);
      setResponse(response);
   }
   catch (Exception ex) {
      throw new ZuulRuntimeException(ex);
   }
   return null;

6. SimpleHostRoutingFilter的forwardRequest()方法：

   private CloseableHttpResponse forwardRequest(CloseableHttpClient httpclient,
         HttpHost httpHost, HttpRequest httpRequest) throws IOException {
      return httpclient.execute(httpHost, httpRequest);
   }

7. 至此回退不生效的原因已找到，将bootstrap.yml中服务的路由方式更改为 serviceId形式，默认转发filter为RibbonRoutingFilter

   routes:
     auth-server:
       strip-prefix: true
       sensitiveHeaders:
       path: /v1/auth-api/**
       serviceId: auth-server
     system-server:
       strip-prefix: true
       sensitiveHeaders:
       path: /v1/system-api/**
       serviceId: system-server

8. RibbonRoutingFilter 中的转发方法：

   protected ClientHttpResponse forward(RibbonCommandContext context) throws Exception {
      Map info = this.helper.debug(context.getMethod(),
            context.getUri(), context.getHeaders(), context.getParams(),
            context.getRequestEntity());
   
      RibbonCommand command = this.ribbonCommandFactory.create(context);
      try {
         ClientHttpResponse response = command.execute();
         this.helper.appendDebug(info, response.getRawStatusCode(), response.getHeaders());
         return response;
      }
      catch (HystrixRuntimeException ex) {
         return handleException(info, ex);
      }
   
   }

9. RibbonCommand 接口继承了HystrixExecutable，重新启动zuul服务，MyServerFallbackProvider全局回退启用正常了；
10. 注：随便写写，可能关键点写的不太详细，各位小伙伴如有异议欢迎指正。

11. 附上小弟久违得订阅号，路过的大佬不嫌弃点个关注