二十.SpringCloud源码剖析-Zuul使用Ribbon负载均衡-RibbonRoutingFilter

素颜马尾好姑娘i 2023-01-12 01:48 134阅读 0赞

## 前言 ##

经过前面几章的学习，我们对Zuul的的详细执行流程，以及内置的Filter都有了一些认识，本篇文章是针对RibbonRoutingFilter做一个详细的分析，跟一下它是如何使用Ribbon对下游的微服务进行负载均衡的。注意：这篇文章是在 《[zuul的执行流程][zuul]》基础上进行延伸的，另外Ribbon的原理见：《[Ribbon负载均衡原理][Ribbon]》

--------------------

回顾一下zuul的执行流程，Zuul的执行流程是这样的

*  首先请求进来会先到达`ZuulController` ，`ZuulController`把请求交给`ZuulServlet`去处理
 *  在`ZuulServelt`会调用 `ZuulRunner` 依次执行： init初始化，`pre`前置filter，`route`路由filter,`post`后置filter, 出现异常会执行 `error` 异常filter
 *  `ZuulRunner`通过 `FilterProcessor` 去执行各种Filter,FilterProcessor通过 `FilterLoader` 加载 各种filters

今天的主角儿 `RibbonRoutingFilter` 是“route”类型的Filter ，它的作用是使用Ribbon对后端的微服务做负载均衡，实现服务的调用，

#### `RibbonRoutingFilter#run` ####

我们直接看它的源码，见`RibbonRoutingFilter#shouldFilter`

@Override
    	public boolean shouldFilter() { 
    		RequestContext ctx = RequestContext.getCurrentContext();
    		//上下文中必须有 serviceId 
    		return (ctx.getRouteHost() == null && ctx.get(SERVICE_ID_KEY) != null
    				&& ctx.sendZuulResponse());
    	}

这里做了简单判断，上下文中必须有 serviceId ，默认的true ，然后会执行run方法 `RibbonRoutingFilter#run`

public Object run() { 
    		RequestContext context = RequestContext.getCurrentContext();
    		this.helper.addIgnoredHeaders();
    		try { 
    			//构建一个Ribbon的命令上下文
    			RibbonCommandContext commandContext = buildCommandContext(context);
    			//执行Ribbon，发送请求
    			ClientHttpResponse response = forward(commandContext);
    			//设置结果
    			setResponse(response);
    			return response;
    		}
    		catch (ZuulException ex) { 
    			throw new ZuulRuntimeException(ex);
    		}
    		catch (Exception ex) { 
    			throw new ZuulRuntimeException(ex);
    		}
    	}
    	//把响应结果设置到RequestContext上下文对象中
    	protected void setResponse(ClientHttpResponse resp)
    			throws ClientException, IOException { 
    			//把响应结果设置到RequestContext上下文对象中
    		RequestContext.getCurrentContext().set("zuulResponse", resp);
    		this.helper.setResponse(resp.getRawStatusCode(),
    				resp.getBody() == null ? null : resp.getBody(), resp.getHeaders());
    	}

#### `RibbonCommandContext` ####

在run方法中构建了一个 `RibbonCommandContext` Ribbon的上下文对象，然后调用 `forward` 方法转发请求 ，通过 `setResponse`方法设置结果

先看一下`buildCommandContext`方法是如何构建`RibbonCommandContext`的

protected RibbonCommandContext buildCommandContext(RequestContext context) { 
    		HttpServletRequest request = context.getRequest();
    		//获取请求头
    		MultiValueMap<String, String> headers = this.helper
    				.buildZuulRequestHeaders(request);
    		//获取参数
    		MultiValueMap<String, String> params = this.helper
    				.buildZuulRequestQueryParams(request);
    		//获取请求的方式 
    		String verb = getVerb(request);
    		//获取请求体中的内容
    		InputStream requestEntity = getRequestBody(request);
    		if (request.getContentLength() < 0 && !verb.equalsIgnoreCase("GET")) { 
    			context.setChunkedRequestBody();
    		}
    		//调用的服务ID
    		String serviceId = (String) context.get(SERVICE_ID_KEY);
    		//是否重试
    		Boolean retryable = (Boolean) context.get(RETRYABLE_KEY);
    		Object loadBalancerKey = context.get(LOAD_BALANCER_KEY);
    		//请求的资源路径
    		String uri = this.helper.buildZuulRequestURI(request);
    
    		// remove double slashes
    		uri = uri.replace("//", "/");
    		//getContentLength 内容长度
    		long contentLength = useServlet31 ? request.getContentLengthLong(): request.getContentLength();
    		//创建一个 RibbonCommandContext
    		return new RibbonCommandContext(serviceId, verb, uri, retryable, headers, params,
    				requestEntity, this.requestCustomizers, contentLength, loadBalancerKey);
    	}

这里从请求中获取了请求头，请求参数，请求体内容，以及服务ID，请求的资源URL等信息封装分 `RibbonCommandContext` ，那RibbonCommandContext 其实就是对下游微服务的请求的上下文数据的封装，下面是 `RibbonCommandContext` 的源码

public class RibbonCommandContext { 
    	private final String serviceId;	//服务id
    	private final String method;	//请求方式 
    	private final String uri;		//请求资源URI
    	private final Boolean retryable;	//重试
    	private final MultiValueMap<String, String> headers; //请求头
    	private final MultiValueMap<String, String> params;	//请求产妇
    	private final List<RibbonRequestCustomizer> requestCustomizers;
    	private InputStream requestEntity;	//请求体内容
    	private Long contentLength;	//内容长度 
    	private Object loadBalancerKey;	//负载均衡器

#### `HttpClientRibbonCommand`的创建 ####

接着我们看一下 `forward` 方法是如何调用下游微服务的 `RibbonRoutingFilter#forward`

protected ClientHttpResponse forward(RibbonCommandContext context) throws Exception { 
    		Map<String, Object> info = this.helper.debug(context.getMethod(),
    				context.getUri(), context.getHeaders(), context.getParams(),
    				context.getRequestEntity());
    		//使用 ribbonCommandFactory 工厂根据context上下文 创建 RibbonCommand 
    		RibbonCommand command = this.ribbonCommandFactory.create(context);
    		try { 
    			//执行请求
    			ClientHttpResponse response = command.execute();
    			this.helper.appendDebug(info, response.getRawStatusCode(), response.getHeaders());
    			return response;
    		}
    		catch (HystrixRuntimeException ex) { 
    			return handleException(info, ex);
    		}
    
    	}

这里 使用 `ribbonCommandFactory` 工厂根据context上下文 创建 `RibbonCommand` ，然后执行 `RibbonCommand.execute` ，我们看一下 `ribbonCommandFactory.create`

@Override
    	public HttpClientRibbonCommand create(final RibbonCommandContext context) { 
    		//获取服务对应的降级
    		FallbackProvider zuulFallbackProvider = getFallbackProvider(context.getServiceId());
    		final String serviceId = context.getServiceId();
    		//获取Ribbon的负载均衡Http客户端
    		final RibbonLoadBalancingHttpClient client = this.clientFactory.getClient(
    				serviceId, RibbonLoadBalancingHttpClient.class);
    	
    		//获取 ILoadBalancer 负载均衡器，设置给 RibbonLoadBalancingHttpClient 
    		client.setLoadBalancer(this.clientFactory.getLoadBalancer(serviceId));
    		//创建一个 HttpClientRibbonCommand 
    		return new HttpClientRibbonCommand(serviceId, client, context, zuulProperties, zuulFallbackProvider,
    				clientFactory.getClientConfig(serviceId));
    	}

`HttpClientRibbonCommandFactory#create` 方法主要是 把服务的降级`FallbackProvider`，以及Ribbon的负载均衡Http客户端，以及`ILoadBalancer` 负载均衡器设置给 `HttpClientRibbonCommand` 对象并返回

`HttpClientRibbonCommand` 是Ribbon的Http客户端，是用来执行相关请求的，看一下它的继承体系它是HystrixCommand的子类  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTQ0OTQxNDg_size_16_color_FFFFFF_t_70]

#### `HttpClientRibbonCommand` 的执行 ####

代码回到 `RibbonRoutingFilter#forward` 方法，接下来分析 `RibbonCommand.execute` 具体执行流程

ClientHttpResponse response = command.execute();

进入这个方法，此时代码来到 `com.netflix.hystrix.HystrixCommand#execute`

public R execute() { 
            try { 
                return queue().get();
            } catch (Exception e) { 
                throw Exceptions.sneakyThrow(decomposeException(e));
            }
        }

进入qeueu方法

public Future<R> queue() { 
            /* * The Future returned by Observable.toBlocking().toFuture() does not implement the * interruption of the execution thread when the "mayInterrupt" flag of Future.cancel(boolean) is set to true; * thus, to comply with the contract of Future, we must wrap around it. */
            // 这里采用了观察者设计模式，使用了异步阻塞方式去执行请求
            final Future<R> delegate = toObservable().toBlocking().toFuture();
        	
            final Future<R> f = new Future<R>() { 
    
                @Override
                public boolean cancel(boolean mayInterruptIfRunning) { 
                  	...省略...
                    return res;
    			}
    
                @Override
                public boolean isCancelled() { 
                    return delegate.isCancelled();
    			}
    
                @Override
                public boolean isDone() { 
                    return delegate.isDone();
    			}
    
                @Override
                public R get() throws InterruptedException, ExecutionException { 
                    return delegate.get();
                }
    
                @Override
                public R get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException { 
                    return delegate.get(timeout, unit);
                }
            	
            };
    
            /* special handling of error states that throw immediately */
            if (f.isDone()) { 
                try { 
                	//获取结果
                    f.get();
                    return f;
                } catch (Exception e) { 
                    Throwable t = decomposeException(e);
                    if (t instanceof HystrixBadRequestException) { 
                        return f;
                    } else if (t instanceof HystrixRuntimeException) { 
                        HystrixRuntimeException hre = (HystrixRuntimeException) t;
                        switch (hre.getFailureType()) { 
    					case COMMAND_EXCEPTION:
    					case TIMEOUT:
    						// we don't throw these types from queue() only from queue().get() as they are execution errors
    						return f;
    					default:
    						// these are errors we throw from queue() as they as rejection type errors
    						throw hre;
    					}
                    } else { 
                        throw Exceptions.sneakyThrow(t);
                    }
                }
            }
    
            return f;
        }

这里采用了观察者设计模式，使用了异步阻塞方式去执行请求，`final Future<R> delegate = toObservable().toBlocking().toFuture();` 这个可以好好去研究一下，最代码会来到 `AbstractRibbonCommand#run`中

@Override
    	protected ClientHttpResponse run() throws Exception { 
    		final RequestContext context = RequestContext.getCurrentContext();
    		//创建请求，实现类是 RibbonApacheHttpRequest
    		RQ request = createRequest();
    		RS response;
    		//可重试的客户端 
    		boolean retryableClient = this.client instanceof AbstractLoadBalancingClient
    				&& ((AbstractLoadBalancingClient)this.client).isClientRetryable((ContextAwareRequest)request);
    		
    		if (retryableClient) { 
    			response = this.client.execute(request, config);
    		} else { 
    			//默认走这里使用负载均衡器执行
    			response = this.client.executeWithLoadBalancer(request, config);
    		}
    		//把结果设置到RequestContext 上下文
    		context.set("ribbonResponse", response);
    
    		// Explicitly close the HttpResponse if the Hystrix command timed out to
    		// release the underlying HTTP connection held by the response.
    		//响应超时，关闭response
    		if (this.isResponseTimedOut()) { 
    			if (response != null) { 
    				response.close();
    			}
    		}
    		//返回结果
    		return new RibbonHttpResponse(response);
    	}

#### `RibbonLoadBalancingHttpClient` Http客户端 ####

关键代码在 `this.client.execute(request, config);` 这里的 client是一个 `RibbonLoadBalancingHttpClient` ，继续跟踪 execute的代码来到 \`AbstractLoadBalancerAwareClient\#executeWithLoadBalancer

public T executeWithLoadBalancer(final S request, final IClientConfig requestConfig) throws ClientException { 
            LoadBalancerCommand<T> command = buildLoadBalancerCommand(request, requestConfig);
    
            try { 
            	//1.调用 LoadBalancerCommand的submit执行请求
                return command.submit(
                    new ServerOperation<T>() { 
                        @Override
                        public Observable<T> call(Server server) { 
                        	//使用服务器重构URI
                            URI finalUri = reconstructURIWithServer(server, request.getUri());
                            S requestForServer = (S) request.replaceUri(finalUri);
                            try { 
                            //2.这里调用了 RibbonLoadBalancingHttpClient.execute方法执行请求
                                return Observable.just(AbstractLoadBalancerAwareClient.this.execute(requestForServer, requestConfig));
                            } 
                            catch (Exception e) { 
                                return Observable.error(e);
                            }
                        }
                    })
                    .toBlocking()
                    .single();
            } catch (Exception e) { 
                Throwable t = e.getCause();
                if (t instanceof ClientException) { 
                    throw (ClientException) t;
                } else { 
                    throw new ClientException(e);
                }
            }
            
        }

方法中有两个重要的代码

*  command.submit ： 调用 `LoadBalancerCommand`的submit，它创建一个Observable 观察者，一旦订阅，该Observable将与`负载均衡器选择的服务器异步执行网络调用。`
 *  AbstractLoadBalancerAwareClient.this.execute：执行具体的服务

#### `LoadBalancerCommand.submit` 提交请求 ####

先看`LoadBalancerCommand.submit`

public Observable<T> submit(final ServerOperation<T> operation) { 
            final ExecutionInfoContext context = new ExecutionInfoContext();
            
            if (listenerInvoker != null) { 
                try { 
                    listenerInvoker.onExecutionStart();
                } catch (AbortExecutionException e) { 
                    return Observable.error(e);
                }
            }
    
            final int maxRetrysSame = retryHandler.getMaxRetriesOnSameServer();
            final int maxRetrysNext = retryHandler.getMaxRetriesOnNextServer();
    
            // Use the load balancer
            //这里在做负载均衡 selectServer
            Observable<T> o = 
                    (server == null ? selectServer() : Observable.just(server))
                    .concatMap(new Func1<Server, Observable<T>>() { 
                        @Override
                        // Called for each server being selected
                        //为每个选定的服务器调用
                        public Observable<T> call(Server server) { 
       ...省略...

很关键的一行代码 `server == null ? selectServer() : Observable.just(server))`它在使用负载均衡选择服务，跟一下 selectServer方法

private Observable<Server> selectServer() { 
            return Observable.create(new OnSubscribe<Server>() { 
                @Override
                public void call(Subscriber<? super Server> next) { 
                    try { 
                    //负载均衡
                        Server server = loadBalancerContext.getServerFromLoadBalancer(loadBalancerURI, loadBalancerKey);   
                        next.onNext(server);
                        next.onCompleted();
                    } catch (Exception e) { 
                        next.onError(e);
                    }
                }
            });
        }

继续跟 `loadBalancerContext.getServerFromLoadBalancer` 方法

public Server getServerFromLoadBalancer(@Nullable URI original, @Nullable Object loadBalancerKey) throws ClientException { 
            String host = null;
            int port = -1;
            if (original != null) { 
                host = original.getHost();
            }
            if (original != null) { 
                Pair<String, Integer> schemeAndPort = deriveSchemeAndPortFromPartialUri(original);        
                port = schemeAndPort.second();
            }
    
            // Various Supported Cases
            // The loadbalancer to use and the instances it has is based on how it was registered
            // In each of these cases, the client might come in using Full Url or Partial URL
            ILoadBalancer lb = getLoadBalancer();
            if (host == null) { 
                // Partial URI or no URI Case
                // well we have to just get the right instances from lb - or we fall back
                if (lb != null){ 
                	//通过 ILoadBalancer的chooseServer方法选择服务
                    Server svc = lb.chooseServer(loadBalancerKey);
                    if (svc == null){ 
                        throw new ClientException(ClientException.ErrorType.GENERAL,
                                "Load balancer does not have available server for client: "
                                        + clientName);
                    }
                    host = svc.getHost();
                    if (host == null){ 
                        throw new ClientException(ClientException.ErrorType.GENERAL,
                                "Invalid Server for :" + svc);
                    }
                    logger.debug("{} using LB returned Server: {} for request {}", new Object[]{ clientName, svc, original});
                    return svc;
                    ...省略...

这里调用了 ILoadBalancer 的 chooseServer方法，继续跟下去会调用 IRule 负载均衡策略的的choose方法选择服务。

#### `RibbonLoadBalancingHttpClient` Http客户端执行请求 ####

选择好服务之后原路返回，请求回到 `AbstractLoadBalancerAwareClient#executeWithLoadBalancer(S, com.netflix.client.config.IClientConfig)，`我们来跟第二个比较重要的代码`RibbonLoadBalancingHttpClient#execute` ， 该方法在执行具体的服务了

@Override
    	public RibbonApacheHttpResponse execute(RibbonApacheHttpRequest request,
    											final IClientConfig configOverride) throws Exception { 
    		IClientConfig config = configOverride != null ? configOverride : this.config;
    		RibbonProperties ribbon = RibbonProperties.from(config);
    		//封装请求配置，超时时间
    		RequestConfig requestConfig = RequestConfig.custom()
    				.setConnectTimeout(ribbon.connectTimeout(this.connectTimeout))
    				.setSocketTimeout(ribbon.readTimeout(this.readTimeout))
    				.setRedirectsEnabled(ribbon.isFollowRedirects(this.followRedirects))
    				.build();
    		//创建请求对象
    		request = getSecureRequest(request, configOverride);
    		final HttpUriRequest httpUriRequest = request.toRequest(requestConfig);
    		//委派给 InternalHttpClient 客户去执行
    		final HttpResponse httpResponse = this.delegate.execute(httpUriRequest);
    		//封装结果返回
    		return new RibbonApacheHttpResponse(httpResponse, httpUriRequest.getURI());
    	}

这里封装了请求配置，创建请求对象，然后交给`apache`的 `InternalHttpClient` 去执行请求，最后把结果封装成`RibbonApacheHttpResponse`返回。

最后响应结果会在`RibbonRoutingFilter`中被设置到`RequestContext` 上下文对象中 ，会通过`SendResponseFilter`去处理把上下文对象中的响应结果写给客户端

到这里整理执行流程结束，我们来这里一下流程  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTQ0OTQxNDg_size_16_color_FFFFFF_t_70 1]

[zuul]: https://blog.csdn.net/u014494148/article/details/113246142
[Ribbon]: https://editor.csdn.net/md/?articleId=108906528
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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTQ0OTQxNDg_size_16_color_FFFFFF_t_70 1]: /images/20221119/e6488ed332b847fa870e4717c61b0c34.png