Nacos Config 动态刷新源码剖析 _新源

不飞则已，一飞冲天；不鸣则已，一鸣惊人。这篇文章主要讲述Nacos Config 动态刷新源码剖析相关的知识，希望能为你提供帮助。
从远端服务器获取变更数据的主要模式有两种：推（push）和拉（pull）。Push 模式简单来说就是服务端主动将数据变更信息推送给客户端，这种模式优点是时效性好，服务端数据发生变更可以立马通知到客户端，但这种模式需要服务端维持与客户端的心跳连接，会增加服务端实现的复杂度，服务端也需要占用更多的资源来维持与客户端的连接。
而 Pull 模式则是客户端主动去服务器请求数据，例如，每间隔10ms就向服务端发起请求获取数据。显而易见pull模式存在时效性问题。请求的间隔也不太好设置，间隔太短，对服务器请求压力过大。间隔时间过长，那么必然会造成时效性很差。而且如果配置长时间不更新，并且存在大量的客户端就会产生大量无效的pull请求。
Nacos 没有采用上述的两种模式，而是采用了长轮询方式结合了推和拉的优点：

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长轮询也是轮询，因此 Nacos 客户端会默认每10ms向服务端发起请求，当客户端请求服务端时会在请求头上携带长轮询的超时时间，默认是30s。而服务端接收到该请求时会hang住请求，为了防止客户端超时会在请求头携带的超时时间上减去500ms，因此默认会hang住请求29.5s。在这期间如果服务端发生了配置变更会产生相应的事件，监听到该事件后，会响应对应的客户端。这样一来客户端不会频繁发起轮询请求，而服务端也不需要维持与客户端的心跳，兼备了时效性和复杂度。

如果你觉得源码枯燥的话，可以选择不看后半部分的源码，先通过这张流程图去了解Nacos动态刷新机制的流程：

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Nacos Config 长轮询源码剖析首先，打开 com.alibaba.cloud.nacos.NacosConfigBootstrapConfiguration 这个类，从类名也可以看出该类是Nacos Config的启动配置类，是Nacos Config自动装配的入口。在该类中的 nacosConfigManager 方法实例化了一个 NacosConfigManager 对象，并注册到容器中：

@Bean @ConditionalOnMissingBean public NacosConfigManager nacosConfigManager( NacosConfigProperties nacosConfigProperties) return new NacosConfigManager(nacosConfigProperties);

在 NacosConfigManager 的构造器中调用了 createConfigService 方法，这是一个静态方法用来创建 ConfigService 对象的单例。

/** * Compatible with old design,It will be perfected in the future. */ static ConfigService createConfigService( NacosConfigProperties nacosConfigProperties) // 双重检查锁模式的单例 if (Objects.isNull(service)) synchronized (NacosConfigManager.class) try if (Objects.isNull(service)) service = NacosFactory.createConfigService( nacosConfigProperties.assembleConfigServiceProperties()); catch (NacosException e) log.error(e.getMessage()); throw new NacosConnectionFailureException( nacosConfigProperties.getServerAddr(), e.getMessage(), e); return service;

ConfigService 的具体实现是 NacosConfigService，在该类的构造器中主要初始化了 HttpAgent 和 ClientWorker 对象。ClientWorker 的构造器中则初始化了几个线程池：

public ClientWorker(final HttpAgent agent, final ConfigFilterChainManager configFilterChainManager, final Properties properties) this.agent = agent; this.configFilterChainManager = configFilterChainManager; // Initialize the timeout parameter init(properties); // 创建具有定时执行功能的单线程池，用于定时执行 checkConfigInfo 方法 this.executor = Executors.newScheduledThreadPool(1, new ThreadFactory() @Override public Thread newThread(Runnable r) Thread t = new Thread(r); t.setName("com.alibaba.nacos.client.Worker." + agent.getName()); t.setDaemon(true); return t; ); // 创建具有定时执行功能的且线程数与cpu核数相对应的线程池，用于根据需要动态刷新的配置文件执行 LongPollingRunnable，因此长轮询任务是可以有多个并行的 this.executorService = Executors .newScheduledThreadPool(Runtime.getRuntime().availableProcessors(), new ThreadFactory() @Override public Thread newThread(Runnable r) Thread t = new Thread(r); t.setName("com.alibaba.nacos.client.Worker.longPolling." + agent.getName()); t.setDaemon(true); return t; ); // 每10ms执行一次 checkConfigInfo 方法 this.executor.scheduleWithFixedDelay(new Runnable() @Override public void run() try checkConfigInfo(); catch (Throwable e) LOGGER.error("[" + agent.getName() + "] [sub-check] rotate check error", e); , 1L, 10L, TimeUnit.MILLISECONDS); private void init(Properties properties) // 长轮询的超时时间，默认为30秒，此参数会被放到请求头中带到服务端，服务端会根据该参数去做长轮询的hold timeout = Math.max(ConvertUtils.toInt(properties.getProperty(PropertyKeyConst.CONFIG_LONG_POLL_TIMEOUT), Constants.CONFIG_LONG_POLL_TIMEOUT), Constants.MIN_CONFIG_LONG_POLL_TIMEOUT); taskPenaltyTime = ConvertUtils .toInt(properties.getProperty(PropertyKeyConst.CONFIG_RETRY_TIME), Constants.CONFIG_RETRY_TIME); this.enableRemoteSyncConfig = Boolean .parseBoolean(properties.getProperty(PropertyKeyConst.ENABLE_REMOTE_SYNC_CONFIG)); /** * Check config info. */ public void checkConfigInfo() // Dispatch taskes. // 获取需要监听的文件数量 int listenerSize = cacheMap.size(); // Round up the longingTaskCount. // 默认一个 LongPollingRunnable 可以处理监听3k个配置文件的变化，超过3k个才会创建新的 LongPollingRunnable int longingTaskCount = (int) Math.ceil(listenerSize / ParamUtil.getPerTaskConfigSize()); if (longingTaskCount > currentLongingTaskCount) for (int i = (int) currentLongingTaskCount; i < longingTaskCount; i++) // The task list is no order.So it maybe has issues when changing. executorService.execute(new LongPollingRunnable(i)); currentLongingTaskCount = longingTaskCount;

LongPollingRunnable 类主要用于检查本地配置，以及长轮询地去服务端获取变更配置的 dataid 和 group，其代码位于 com.alibaba.nacos.client.config.impl.ClientWorker 类，代码如下：

class LongPollingRunnable implements Runnable private final int taskId; public LongPollingRunnable(int taskId) this.taskId = taskId; @Override public void run() List< CacheData> cacheDatas = new ArrayList< CacheData> (); List< String> inInitializingCacheList = new ArrayList< String> (); try // check failover config // 遍历本地缓存的配置 for (CacheData cacheData : cacheMap.values()) if (cacheData.getTaskId() == taskId) cacheDatas.add(cacheData); try // 检查本地配置 checkLocalConfig(cacheData); if (cacheData.isUseLocalConfigInfo()) cacheData.checkListenerMd5(); catch (Exception e) LOGGER.error("get local config info error", e); // check server config // 通过长轮询检查服务端配置 List< String> changedGroupKeys = checkUpdateDataIds(cacheDatas, inInitializingCacheList); if (!CollectionUtils.isEmpty(changedGroupKeys)) LOGGER.info("get changedGroupKeys:" + changedGroupKeys); for (String groupKey : changedGroupKeys) String[] key = GroupKey.parseKey(groupKey); String dataId = key[0]; String group = key[1]; String tenant = null; if (key.length == 3) tenant = key[2]; try String[] ct = getServerConfig(dataId, group, tenant, 3000L); CacheData cache = cacheMap.get(GroupKey.getKeyTenant(dataId, group, tenant)); cache.setContent(ct[0]); if (null != ct[1]) cache.setType(ct[1]); LOGGER.info("[] [data-received] dataId=, group=, tenant=, md5=, content=, type=", agent.getName(), dataId, group, tenant, cache.getMd5(), ContentUtils.truncateContent(ct[0]), ct[1]); catch (NacosException ioe) String message = String .format("[%s] [get-update] get changed config exception. dataId=%s, group=%s, tenant=%s", agent.getName(), dataId, group, tenant); LOGGER.error(message, ioe); for (CacheData cacheData : cacheDatas) if (!cacheData.isInitializing() || inInitializingCacheList .contains(GroupKey.getKeyTenant(cacheData.dataId, cacheData.group, cacheData.tenant))) cacheData.checkListenerMd5(); cacheData.setInitializing(false); inInitializingCacheList.clear(); executorService.execute(this); catch (Throwable e) // If the rotation training task is abnormal, the next execution time of the task will be punished LOGGER.error("longPolling error : ", e); executorService.schedule(this, taskPenaltyTime, TimeUnit.MILLISECONDS);

上面有个 checkUpdateDataIds 方法，用于获取发生变更了的配置文件的dataId列表，它同样位于 ClientWorker 内。如下：

/** * Fetch the dataId list from server. * * @param cacheDatasCacheDatas for config infomations. * @param inInitializingCacheList initial cache lists. * @return String include dataId and group (ps: it maybe null). * @throws Exception Exception. */ List< String> checkUpdateDataIds(List< CacheData> cacheDatas, List< String> inInitializingCacheList) throws Exception // 拼接出配置文件的唯一标识 StringBuilder sb = new StringBuilder(); for (CacheData cacheData : cacheDatas) if (!cacheData.isUseLocalConfigInfo()) sb.append(cacheData.dataId).append(WORD_SEPARATOR); sb.append(cacheData.group).append(WORD_SEPARATOR); if (StringUtils.isBlank(cacheData.tenant)) sb.append(cacheData.getMd5()).append(LINE_SEPARATOR); else sb.append(cacheData.getMd5()).append(WORD_SEPARATOR); sb.append(cacheData.getTenant()).append(LINE_SEPARATOR); if (cacheData.isInitializing()) // It updates when cacheData occours in cacheMap by first time. inInitializingCacheList .add(GroupKey.getKeyTenant(cacheData.dataId, cacheData.group, cacheData.tenant)); boolean isInitializingCacheList = !inInitializingCacheList.isEmpty(); return checkUpdateConfigStr(sb.toString(), isInitializingCacheList); /** * Fetch the updated dataId list from server. * * @param probeUpdateStringupdated attribute string value. * @param isInitializingCacheList initial cache lists. * @return The updated dataId list(ps: it maybe null). * @throws IOException Exception. */ List< String> checkUpdateConfigStr(String probeUpdateString, boolean isInitializingCacheList) throws Exception Map< String, String> params = new HashMap< String, String> (2); params.put(Constants.PROBE_MODIFY_REQUEST, probeUpdateString); Map< String, String> headers = new HashMap< String, String> (2); // 长轮询的超时时间 headers.put("Long-Pulling-Timeout", "" + timeout); // told server do not hang me up if new initializing cacheData added in if (isInitializingCacheList) headers.put("Long-Pulling-Timeout-No-Hangup", "true"); if (StringUtils.isBlank(probeUpdateString)) return Collections.emptyList(); try // In order to prevent the server from handling the delay of the clients long task, // increase the clients read timeout to avoid this problem.long readTimeoutMs = timeout + (long) Math.round(timeout > > 1); // 向服务端发起一个http请求，该请求在服务端配置没有变更的情况下默认会hang住30s HttpRestResult< String> result = agent .httpPost(Constants.CONFIG_CONTROLLER_PATH + "/listener", headers, params, agent.getEncode(), readTimeoutMs); if (result.ok()) setHealthServer(true); // 响应状态是成功则解析响应体得到 dataId、group、tenant 等信息并返回 return parseUpdateDataIdResponse(result.getData()); else setHealthServer(false); LOGGER.error("[] [check-update] get changed dataId error, code: ", agent.getName(), result.getCode()); catch (Exception e) setHealthServer(false); LOGGER.error("[" + agent.getName() + "] [check-update] get changed dataId exception", e); throw e; return Collections.emptyList();

客户端对 listener 接口的请求会进入到服务端的 com.alibaba.nacos.config.server.controller.ConfigController#listener 方法进行处理，该方法主要是调用了 com.alibaba.nacos.config.server.controller.ConfigServletInner#doPollingConfig 方法。代码如下：

/** * 轮询接口 */ public String doPollingConfig(HttpServletRequest request, HttpServletResponse response, Map< String, String> clientMd5Map, int probeRequestSize) throws IOException, ServletException // 如果支持长轮询则进入长轮询的流程 if (LongPollingService.isSupportLongPolling(request)) longPollingService.addLongPollingClient(request, response, clientMd5Map, probeRequestSize); return HttpServletResponse.SC_OK + ""; // else 兼容短轮询逻辑 List< String> changedGroups = MD5Util.compareMd5(request, response, clientMd5Map); // 兼容短轮询result String oldResult = MD5Util.compareMd5OldResult(changedGroups); String newResult = MD5Util.compareMd5ResultString(changedGroups); String version = request.getHeader(Constants.CLIENT_VERSION_HEADER); if (version == null) version = "2.0.0"; int versionNum = Protocol.getVersionNumber(version); /** * 2.0.4版本以前, 返回值放入header中 */ if (versionNum < START_LONGPOLLING_VERSION_NUM) response.addHeader(Constants.PROBE_MODIFY_RESPONSE, oldResult); response.addHeader(Constants.PROBE_MODIFY_RESPONSE_NEW, newResult); else request.setAttribute("content", newResult); // 禁用缓存 response.setHeader("Pragma", "no-cache"); response.setDateHeader("Expires", 0); response.setHeader("Cache-Control", "no-cache,no-store"); response.setStatus(HttpServletResponse.SC_OK); return HttpServletResponse.SC_OK + "";

我们主要关注上面的 com.alibaba.nacos.config.server.service.LongPollingService#addLongPollingClient 长轮询流程的方法。代码如下：

public void addLongPollingClient(HttpServletRequest req, HttpServletResponse rsp, Map< String, String> clientMd5Map, int probeRequestSize) String str = req.getHeader(LongPollingService.LONG_POLLING_HEADER); String noHangUpFlag = req.getHeader(LongPollingService.LONG_POLLING_NO_HANG_UP_HEADER); String appName = req.getHeader(RequestUtil.CLIENT_APPNAME_HEADER); String tag = req.getHeader("Vipserver-Tag"); int delayTime = SwitchService.getSwitchInteger(SwitchService.FIXED_DELAY_TIME, 500); /** * 提前500ms返回响应，为避免客户端超时 @qiaoyi.dingqy 2013.10.22改动add delay time for LoadBalance */ long timeout = Math.max(10000, Long.parseLong(str) - delayTime); if (isFixedPolling()) timeout = Math.max(10000, getFixedPollingInterval()); // do nothing but set fix polling timeout else long start = System.currentTimeMillis(); List< String> changedGroups = MD5Util.compareMd5(req, rsp, clientMd5Map); if (changedGroups.size() > 0) generateResponse(req, rsp, changedGroups); LogUtil.clientLog.info("||||||", System.currentTimeMillis() - start, "instant", RequestUtil.getRemoteIp(req), "polling", clientMd5Map.size(), probeRequestSize, changedGroups.size()); return; else if (noHangUpFlag != null & & noHangUpFlag.equalsIgnoreCase(TRUE_STR)) LogUtil.clientLog.info("||||||", System.currentTimeMillis() - start, "nohangup", RequestUtil.getRemoteIp(req), "polling", clientMd5Map.size(), probeRequestSize, changedGroups.size()); return; String ip = RequestUtil.getRemoteIp(req); // 一定要由HTTP线程调用，否则离开后容器会立即发送响应 final AsyncContext asyncContext = req.startAsync(); // AsyncContext.setTimeout()的超时时间不准，所以只能自己控制 asyncContext.setTimeout(0L); // 在 ClientLongPolling 的 run 方法会将 ClientLongPolling 实例（携带了本次请求的相关信息）放入 allSubs 中，然后会在29.5s后再执行另一个 Runnable，该 Runnable 用于等待29.5s后依旧没有相应的配置变更时对客户端进行响应，并将相应的 ClientLongPolling 实例从 allSubs 中移出 scheduler.execute( new ClientLongPolling(asyncContext, clientMd5Map, ip, probeRequestSize, timeout, appName, tag));

而 LongPollingService 实现了 AbstractEventListener，也就是说能接收事件通知，在其 com.alibaba.nacos.config.server.service.LongPollingService#onEvent 方法中可以看到，它关注的是 LocalDataChangeEvent 事件：

@Override public void onEvent(Event event) if (isFixedPolling()) // ignore else if (event instanceof LocalDataChangeEvent) LocalDataChangeEvent evt = (LocalDataChangeEvent)event; scheduler.execute(new DataChangeTask(evt.groupKey, evt.isBeta, evt.betaIps));

在nacos上修改配置后就会产生 LocalDataChangeEvent 事件，此时 LongPollingService 也就能监听到，当收到该事件时就会遍历 allSubs，找到匹配的请求并将 groupKey 返回给客户端。具体代码在 DataChangeTask 中：

class DataChangeTask implements Runnable @Override public void run() try ConfigService.getContentBetaMd5(groupKey); for (Iterator< ClientLongPolling> iter = allSubs.iterator(); iter.hasNext(); ) ClientLongPolling clientSub = iter.next(); if (clientSub.clientMd5Map.containsKey(groupKey)) // 如果beta发布且不在beta列表直接跳过 if (isBeta & & !betaIps.contains(clientSub.ip)) continue; // 如果tag发布且不在tag列表直接跳过 if (StringUtils.isNotBlank(tag) & & !tag.equals(clientSub.tag)) continue; getRetainIps().put(clientSub.ip, System.currentTimeMillis()); iter.remove(); // 删除订阅关系 LogUtil.clientLog.info("||||||", (System.currentTimeMillis() - changeTime), "in-advance", RequestUtil.getRemoteIp((HttpServletRequest)clientSub.asyncContext.getRequest()), "polling", clientSub.clientMd5Map.size(), clientSub.probeRequestSize, groupKey); clientSub.sendResponse(Arrays.asList(groupKey)); catch (Throwable t) LogUtil.defaultLog.error("data change error:" + t.getMessage(), t.getCause()); DataChangeTask(String groupKey) this(groupKey, false, null); DataChangeTask(String groupKey, boolean isBeta, List< String> betaIps) this(groupKey, isBeta, betaIps, null); DataChangeTask(String groupKey, boolean isBeta, List< String> betaIps, String tag) this.groupKey = groupKey; this.isBeta = isBeta; this.betaIps = betaIps; this.tag = tag; final String groupKey; final long changeTime = System.currentTimeMillis(); final boolean isBeta; final List< String> betaIps; final String tag;

当客户端收到变更的dataid+group后，就会去服务端获取最新的配置数据，并更新本地数据 cacheData，然后发送数据变更事件，整个流程结束。

获取服务端最新配置数据的方法：com.alibaba.nacos.client.config.impl.ClientWorker#getServerConfig
发送数据变更事件的方法：com.alibaba.nacos.client.config.impl.CacheData#checkListenerMd5

【Nacos Config 动态刷新源码剖析】最后附上一张流程与源码的对应图：