SpringCloudFeign引入feign-httpclient导致的坑

本是古典何须时尚 2021-06-24 13:58 804阅读 0赞

SpringCloudFeign底层是通过http/https协议进行通信，默认是采用`java.net.HttpURLConnection`，每次请求都会建立、关闭连接，为了性能考虑，可以引入httpclient、okhttp作为底层的通信框架。

**maven坐标如下：**

<dependency>
     <groupId>io.github.openfeign</groupId>
     <artifactId>feign-httpclient</artifactId>
     <version>9.5.0</version>
    </dependency>

在项目中我们采用SpringCloud（Dalston.SR4）技术栈，为了性能考虑也引入了httpclient对feign的支持。当一次项目压测过程中，发现请求的tps达到一定值时，整个请求的耗时明显上升了，后来通过日志分析，发现请求调用发起时到服务端接受请求耗费了5s以上，最后聚焦到feign调用的底层实现(中间也走了很多弯路，一度怀疑网络层面是否存在问题)，通过代码分析，发现feign初始化client的代码如下：

@Configuration
    @ConditionalOnClass(ApacheHttpClient.class)
    @ConditionalOnProperty(value = "feign.httpclient.enabled", matchIfMissing = true)
    class HttpClientFeignLoadBalancedConfiguration {
    
    	@Autowired(required = false)
    	private HttpClient httpClient;
    
    	@Bean
    	@ConditionalOnMissingBean(Client.class)
    	public Client feignClient(CachingSpringLoadBalancerFactory cachingFactory,
    							  SpringClientFactory clientFactory) {
    		ApacheHttpClient delegate;
    		if (this.httpClient != null) {
    			delegate = new ApacheHttpClient(this.httpClient);
    		} else {
    			delegate = new ApacheHttpClient();
    		}
    		return new LoadBalancerFeignClient(delegate, cachingFactory, clientFactory);
    	}
    }

项目中我们没有显示的声明`org.apache.http.client.HttpClient`，所以走到了`delegate = new ApacheHttpClient();`这段逻辑，继续往下分析，找到`org.apache.http.impl.conn.PoolingHttpClientConnectionManager`初始化方法：

public PoolingHttpClientConnectionManager(
            final HttpClientConnectionOperator httpClientConnectionOperator,
            final HttpConnectionFactory<HttpRoute, ManagedHttpClientConnection> connFactory,
            final long timeToLive, final TimeUnit tunit) {
            super();
            this.configData = new ConfigData();
            this.pool = new CPool(new InternalConnectionFactory(
                    this.configData, connFactory), 2, 20, timeToLive, tunit);
            this.pool.setValidateAfterInactivity(2000);
            this.connectionOperator = Args.notNull(httpClientConnectionOperator, "HttpClientConnectionOperator");
            this.isShutDown = new AtomicBoolean(false);
        }
        
    public CPool(
                final ConnFactory<HttpRoute, ManagedHttpClientConnection> connFactory,
                final int defaultMaxPerRoute, final int maxTotal,
                final long timeToLive, final TimeUnit tunit) {
            super(connFactory, defaultMaxPerRoute, maxTotal);
            this.timeToLive = timeToLive;
            this.tunit = tunit;
        }

到这里一眼就能看出问题了，默认的defaultMaxPerRoute=2，maxTotal=20，所以根本原因已找到，解决方法就是不用默认构造的`org.apache.http.client.HttpClient`，在应用中自己申明一个HttpClient实例bean：

@Bean(destroyMethod = "close")
        public CloseableHttpClient httpClient() {
            PoolingHttpClientConnectionManager connectionManager = new PoolingHttpClientConnectionManager();
            connectionManager.setMaxTotal(400);
            connectionManager.setDefaultMaxPerRoute(100);
    
            RequestConfig requestConfig = RequestConfig.custom().setConnectionRequestTimeout(2000)//从连接池获取连接等待超时时间
                    .setConnectTimeout(2000)//请求超时时间
                    .setSocketTimeout(15000)//等待服务响应超时时间
                    .build();
            HttpClientBuilder httpClientBuilder = HttpClientBuilder.create().setConnectionManager(connectionManager)
                    .setDefaultRequestConfig(requestConfig)
                    //自定义重试策略，针对502和503重试一次
                    .setServiceUnavailableRetryStrategy(new CustomizedServiceUnavailableRetryStrategy())
                    .evictExpiredConnections();
            return httpClientBuilder.build();
        }

至此，问题已经解决。

### 总结： ###

> 引入新技术栈时，一定要阅读相关文档了解组件的配置化参数信息(默认值往往在遇到高并发场景无法满足)，特别是对于基于springboot构建的应用，往往由于自动化的配置，导致忽略了重要参数的指定。