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Gateway 网关坑我！被这个404 问题折腾了一年？

news 2025/9/17 2:15:07

大家好，我是小富～

最近同事找我帮忙排查一个"诡异"的 Bug，说困扰了他们一年多一直没解决。我接手后花了一些时间定位到了问题根源，今天就来跟大家分享一下这个问题的排查过程和解决方案。

问题描述

同事使用的是 SpringCloud Gateway 3.0.1 + JDK8，整合了 Nacos 做动态路由配置。问题是：每次修改 Nacos 的路由配置后，网关的 API 请求就会出现 404 错误，但重启网关后又能恢复正常。

听到这个问题，我的第一反应是：Nacos 配置更新后，网关的缓存数据可能没有及时更新。带着这个猜想，我开始深入排查。

环境准备

首先准备了 3 个后端服务实例，端口分别为 8103、12040、12041，在 Nacos 中配置了对应的网关路由：xiaofu-8103、xiaofu-12040、xiaofu-12041，并将它们放在同一个权重组 xiaofu-group 中，实现基于权重的负载均衡。

- id: xiaofu-8103uri: http://127.0.0.1:8103/predicates:- Weight=xiaofu-group, 2- Path=/test/version1/**filters:- RewritePath=/test/version1/(?<segment>.*),/$\{segment}
- id: xiaofu-12040uri: http://127.0.0.1:12040/predicates:- Weight=xiaofu-group, 1- Path=/test/version1/**filters:- RewritePath=/test/version1/(?<segment>.*),/$\{segment}
- id: xiaofu-12041uri: http://127.0.0.1:12041/predicates:- Weight=xiaofu-group, 2- Path=/test/version1/**filters:- RewritePath=/test/version1/(?<segment>.*),/$\{segment}

使用 JMeter 进行持续请求测试，为了便于日志追踪，给每个请求参数都添加了随机数。

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准备完成后启动 JMeter 循环请求，观察到三个实例都有日志输出，说明网关的负载均衡功能正常。

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问题排查

为了获取更详细的日志信息，我将网关的日志级别调整为 TRACE。

启动 JMeter 后，随机修改三个实例的路由属性（uri、port、predicates、filters），请求没有出现报错，网关控制台也显示了更新后的路由属性，说明 Nacos 配置变更已成功同步到网关。

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接下来尝试去掉一个实例 xiaofu-12041，这时发现 JMeter 请求开始出现 404 错误，成功复现问题！

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查看网关控制台日志时，惊奇地发现已删除的实例 xiaofu-12041 的路由配置仍然存在，甚至还被选中（chosen）处理请求。问题根源找到了：虽然 Nacos 中删除了实例路由配置，但网关在实际负载均衡时仍然使用旧的路由数据。

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继续深入排查，发现在路由的权重信息（Weights attr）中也存在旧的路由数据。至此基本确定问题：在计算实例权重和负载均衡时，网关使用了陈旧的缓存数据。

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源码分析

通过分析源码，发现了一个专门计算权重的过滤器 WeightCalculatorWebFilter。它内部维护了一个 groupWeights 变量来存储路由权重信息。当配置变更事件发生时，会执行 addWeightConfig(WeightConfig weightConfig) 方法来更新权重配置。

@Override
public void onApplicationEvent(ApplicationEvent event) {if (event instanceof PredicateArgsEvent) {handle((PredicateArgsEvent) event);}else if (event instanceof WeightDefinedEvent) {addWeightConfig(((WeightDefinedEvent) event).getWeightConfig());}else if (event instanceof RefreshRoutesEvent && routeLocator != null) {if (routeLocatorInitialized.compareAndSet(false, true)) {routeLocator.ifAvailable(locator -> locator.getRoutes().blockLast());}else {routeLocator.ifAvailable(locator -> locator.getRoutes().subscribe());}}}

addWeightConfig 方法的注释明确说明：该方法仅创建新的 GroupWeightConfig，而不进行修改。这意味着它只能新建或覆盖路由权重，无法清理已删除的路由权重信息。

void addWeightConfig(WeightConfig weightConfig) {String group = weightConfig.getGroup();GroupWeightConfig config;// only create new GroupWeightConfig rather than modify// and put at end of calculations. This avoids concurency problems// later during filter execution.if (groupWeights.containsKey(group)) {config = new GroupWeightConfig(groupWeights.get(group));}else {config = new GroupWeightConfig(group);}final AtomicInteger index = new AtomicInteger(0);....省略.....if (log.isTraceEnabled()) {log.trace("Recalculated group weight config " + config);}// only update after all calculationsgroupWeights.put(group, config);}

解决方案

找到问题根源后，解决方案就清晰了

开始我怀疑可能是springcloud gateway 版本问题，将版本升级到了4.1.0，但结果还是存在这个问题。

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看来只能手动更新缓存，需要监听 Nacos 路由配置变更事件，获取最新路由配置，并更新 groupWeights 中的权重数据。

以下是实现的解决方案代码：

@Slf4j
@Configuration
public class WeightCacheRefresher {@Autowiredprivate WeightCalculatorWebFilter weightCalculatorWebFilter;@Autowiredprivate RouteDefinitionLocator routeDefinitionLocator;@Autowiredprivate ApplicationEventPublisher publisher;/*** 监听路由刷新事件，同步更新权重缓存*/@EventListener(RefreshRoutesEvent.class)public void onRefreshRoutes() {log.info("检测到路由刷新事件，准备同步更新权重缓存");syncWeightCache();}/*** 同步权重缓存与当前路由配置*/public void syncWeightCache() {try {// 获取 groupWeights 字段Field groupWeightsField = WeightCalculatorWebFilter.class.getDeclaredField("groupWeights");groupWeightsField.setAccessible(true);// 获取当前的 groupWeights 值@SuppressWarnings("unchecked")Map<String, Object> groupWeights = (Map<String, Object>) groupWeightsField.get(weightCalculatorWebFilter);if (groupWeights == null) {log.warn("未找到 groupWeights 缓存");return;}log.info("当前 groupWeights 缓存: {}", groupWeights.keySet());// 获取当前所有路由的权重组和路由IDfinal Set<String> currentRouteIds = new HashSet<>();final Map<String, Map<String, Integer>> currentGroupRouteWeights = new HashMap<>();routeDefinitionLocator.getRouteDefinitions().collectList().subscribe(definitions -> {definitions.forEach(def -> {currentRouteIds.add(def.getId());def.getPredicates().stream().filter(predicate -> predicate.getName().equals("Weight")).forEach(predicate -> {Map<String, String> args = predicate.getArgs();String group = args.getOrDefault("_genkey_0", "unknown");int weight = Integer.parseInt(args.getOrDefault("_genkey_1", "0"));// 记录每个组中当前存在的路由及其权重currentGroupRouteWeights.computeIfAbsent(group, k -> new HashMap<>()).put(def.getId(), weight);});});log.info("当前路由配置中的路由ID: {}", currentRouteIds);log.info("当前路由配置中的权重组: {}", currentGroupRouteWeights);// 检查每个权重组，移除不存在的路由，更新权重变化的路由Set<String> groupsToRemove = new HashSet<>();Set<String> groupsToUpdate = new HashSet<>();for (String group : groupWeights.keySet()) {if (!currentGroupRouteWeights.containsKey(group)) {// 整个权重组不再存在groupsToRemove.add(group);log.info("权重组 [{}] 不再存在于路由配置中，将被移除", group);continue;}// 获取该组中当前配置的路由ID和权重Map<String, Integer> configuredRouteWeights = currentGroupRouteWeights.get(group);// 获取该组中缓存的权重配置Object groupWeightConfig = groupWeights.get(group);try {// 获取 weights 字段Field weightsField = groupWeightConfig.getClass().getDeclaredField("weights");weightsField.setAccessible(true);@SuppressWarnings("unchecked")LinkedHashMap<String, Integer> weights = (LinkedHashMap<String, Integer>) weightsField.get(groupWeightConfig);// 找出需要移除的路由IDSet<String> routesToRemove = weights.keySet().stream().filter(routeId -> !configuredRouteWeights.containsKey(routeId)).collect(Collectors.toSet());// 找出权重发生变化的路由IDSet<String> routesWithWeightChange = new HashSet<>();for (Map.Entry<String, Integer> entry : weights.entrySet()) {String routeId = entry.getKey();Integer cachedWeight = entry.getValue();if (configuredRouteWeights.containsKey(routeId)) {Integer configuredWeight = configuredRouteWeights.get(routeId);if (!cachedWeight.equals(configuredWeight)) {routesWithWeightChange.add(routeId);log.info("路由 [{}] 的权重从 {} 变为 {}", routeId, cachedWeight, configuredWeight);}}}// 找出新增的路由IDSet<String> newRoutes = configuredRouteWeights.keySet().stream().filter(routeId -> !weights.containsKey(routeId)).collect(Collectors.toSet());if (!routesToRemove.isEmpty() || !routesWithWeightChange.isEmpty() || !newRoutes.isEmpty()) {log.info("权重组 [{}] 中有变化：删除 {}，权重变化 {}，新增 {}",group, routesToRemove, routesWithWeightChange, newRoutes);// 如果有任何变化，我们将重新计算整个组的权重groupsToUpdate.add(group);}// 首先，移除需要删除的路由for (String routeId : routesToRemove) {weights.remove(routeId);}// 如果权重组中没有剩余路由，则移除整个组if (weights.isEmpty()) {groupsToRemove.add(group);log.info("权重组 [{}] 中没有剩余路由，将移除整个组", group);}} catch (Exception e) {log.error("处理权重组 [{}] 时出错", group, e);}}// 移除不再需要的权重组for (String group : groupsToRemove) {groupWeights.remove(group);log.info("已移除权重组: {}", group);}// 更新需要重新计算的权重组for (String group : groupsToUpdate) {try {// 获取该组中当前配置的路由ID和权重Map<String, Integer> configuredRouteWeights = currentGroupRouteWeights.get(group);// 移除旧的权重组配置groupWeights.remove(group);log.info("已移除权重组 [{}] 以便重新计算", group);// 为每个路由创建 WeightConfig 并调用 addWeightConfig 方法Method addWeightConfigMethod = WeightCalculatorWebFilter.class.getDeclaredMethod("addWeightConfig", WeightConfig.class);addWeightConfigMethod.setAccessible(true);for (Map.Entry<String, Integer> entry : configuredRouteWeights.entrySet()) {String routeId = entry.getKey();Integer weight = entry.getValue();WeightConfig weightConfig = new WeightConfig(routeId);weightConfig.setGroup(group);weightConfig.setWeight(weight);addWeightConfigMethod.invoke(weightCalculatorWebFilter, weightConfig);log.info("为路由 [{}] 添加权重配置：组 [{}]，权重 {}", routeId, group, weight);}} catch (Exception e) {log.error("重新计算权重组 [{}] 时出错", group, e);}}log.info("权重缓存同步完成，当前缓存的权重组: {}", groupWeights.keySet());});} catch (Exception e) {log.error("同步权重缓存失败", e);}}
}

网上找一圈并没发现官方的修改意见，可能是咱们使用方式不对导致的，要不如此明显的BUG早就有人改了吧！

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