背景
gateway中多实例请求转发，默认采用轮训转发策略。在有些场景下，某些请求想固定到某一台实例上，这里通过重写默认负载均衡策略的方式实现。
以下代码为，大文件分片上传，多实例场景，根据文件md5和实例总数取模，选取处理服务实例。保证同一文件在固定实例上进行处理，保证最后的文件合并不会有问题。
实现
Gateway有两种客户端负载均衡器，LoadBalancerClientFilter和ReactiveLoadBalancerClientFilter。LoadBalancerClientFilter使用一个Ribbon的阻塞式LoadBalancerClient，Gateway建议使用ReactiveLoadBalancerClientFilter。
以下通过重写LoadBalancerClientFilter实现。
重写代码
public class IdUploadLoadBalancerClientFilter extends LoadBalancerClientFilter {private static final Log log = LogFactory.getLog(IdUploadLoadBalancerClientFilter.class);private static final String ID_INTEGRATION = "id-integration";private static final List<String> UPLOAD_URL_LIST = Lists.newArrayList("/v5/base/access/data/multipart/upload", "/v5/base/access/data/multipart/merge");private LoadBalancerProperties properties;@Resourceprivate NacosDiscoveryClient nacosDiscoveryClient;public IdUploadLoadBalancerClientFilter(LoadBalancerClient loadBalancer, LoadBalancerProperties properties) {super(loadBalancer, properties);this.properties = properties;}@Overridepublic Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {URI url = exchange.getAttribute(GATEWAY_REQUEST_URL_ATTR);String schemePrefix = exchange.getAttribute(GATEWAY_SCHEME_PREFIX_ATTR);if (url == null|| (!"lb".equals(url.getScheme()) && !"lb".equals(schemePrefix))) {return chain.filter(exchange);}// preserve the original urladdOriginalRequestUrl(exchange, url);if (log.isTraceEnabled()) {log.trace("LoadBalancerClientFilter url before: " + url);}ServiceInstance instance = choose(exchange);String serviceId = instance.getServiceId();//判断当前实例id是否为id-integrationif (StringUtils.equalsIgnoreCase(serviceId, ID_INTEGRATION)) {ServerHttpRequest request = exchange.getRequest();HttpMethod httpMethod = request.getMethod();String path = request.getURI().getPath();String contentType = String.join(";", Objects.requireNonNull(request.getHeaders().get("Content-Type")));if (httpMethod != null && httpMethod.matches(HttpMethod.POST.name()) && UPLOAD_URL_LIST.contains(path)) {boolean isUploadLoad = StringUtils.containsIgnoreCase(contentType, MediaType.MULTIPART_FORM_DATA_VALUE);String fileMd5 = null;if (isUploadLoad) {fileMd5 = String.join(";", Objects.requireNonNull(request.getHeaders().get("fileMd5")));} else {List<String> fileMd5List = request.getQueryParams().get("fileMd5");if (fileMd5List != null && fileMd5List.size() > 0) {fileMd5 = fileMd5List.get(0);}}if (StringUtils.isNotBlank(fileMd5)) {List<ServiceInstance> instances = nacosDiscoveryClient.getInstances(ID_INTEGRATION);int targetIndex = Math.abs(fileMd5.hashCode()) % instances.size();ServiceInstance serviceInstance = instances.get(targetIndex);RibbonLoadBalancerClient.RibbonServer ribbonServer = (RibbonLoadBalancerClient.RibbonServer) instance;NacosServer nacosServer = (NacosServer) ribbonServer.getServer();nacosServer.setHost(serviceInstance.getHost());nacosServer.setPort(serviceInstance.getPort());Map<String, String> metadata = ribbonServer.getMetadata();boolean secure = ribbonServer.isSecure();instance = new RibbonLoadBalancerClient.RibbonServer(serviceId, nacosServer, secure, metadata);}}}if (instance == null) {throw NotFoundException.create(properties.isUse404(),"Unable to find instance for " + url.getHost());}URI uri = exchange.getRequest().getURI();// if the `lb:<scheme>` mechanism was used, use `<scheme>` as the default,// if the loadbalancer doesn't provide one.String overrideScheme = instance.isSecure() ? "https" : "http";if (schemePrefix != null) {overrideScheme = url.getScheme();}URI requestUrl = loadBalancer.reconstructURI(new DelegatingServiceInstance(instance, overrideScheme), uri);if (log.isTraceEnabled()) {log.trace("LoadBalancerClientFilter url chosen: " + requestUrl);}exchange.getAttributes().put(GATEWAY_REQUEST_URL_ATTR, requestUrl);return chain.filter(exchange);}}bean配置
@Beanpublic LoadBalancerClientFilter loadBalancerClientFilter(LoadBalancerClient client,LoadBalancerProperties properties) {return new IdUploadLoadBalancerClientFilter(client, properties);}
