Nacos-配置中心原理解析
文章系列
【一、Nacos-配置中心原理解析】
【二、Nacos-配置中心原理解析】
【三、Nacos注册中心集群数据一致性问题】
一、配置中心原理猜想
如果你来实现一个配置中心，你觉得有哪些需求点？
- 配置信息存储
- 配置中心控制台
- 配置中心文件发生变更后，数据同步：客户端定时任务-pull、服务端广播通知-push、长轮询机制)
- 配置中心集群(leader、follower，主节点选举，数据一致性)
二、Nacos配置中心原理解析
注意：本文档是基于 nacos 1.1.3 版本编写。
<dependency>
<groupId>com.alibaba.nacos</groupId>
<artifactId>nacos-client</artifactId>
<version>1.1.3</version>
</dependency>
基于Nacos SDK 调用
public class NacosTest {
public static void main(String[] args) throws Exception {
Properties properties = new Properties();
properties.put("serverAddr", "服务端地址");
properties.put("namespace", "namespace");
// 通过指定参数，创建一个 configService
ConfigService configService = NacosFactory.createConfigService(properties);
String dataId = "testId";
String group = "testGroup";
// 通过dataId、group获取配置
String config = configService.getConfig(dataId, group, 3000);
System.out.println(config);
// 监听服务端配置变更
configService.addListener(dataId, group, new Listener() {
@Override
public Executor getExecutor() {
return null;
}
@Override
public void receiveConfigInfo(String configInfo) {
System.out.println("-------配置发生变更，变更后的配置：" + configInfo);
}
});
CountDownLatch countDownLatch = new CountDownLatch(1);
countDownLatch.await();
}
}
2.1 NacosFactory.createConfigService(properties)
public class ConfigFactory {
/**
* Create Config
*
* @param properties init param
* @return ConfigService
* @throws NacosException Exception
*/
public static ConfigService createConfigService(Properties properties) throws NacosException {
try {
Class<?> driverImplClass = Class.forName("com.alibaba.nacos.client.config.NacosConfigService");
// 获取带Properties参数的构造函数
Constructor constructor = driverImplClass.getConstructor(Properties.class);
// 反射创建
ConfigService vendorImpl = (ConfigService) constructor.newInstance(properties);
return vendorImpl;
} catch (Throwable e) {
throw new NacosException(NacosException.CLIENT_INVALID_PARAM, e);
}
}
}
通过代码分析，底层主要是获取带Properties参数的构造函数，通过反射创建 NacosConfigService 对象。
2.1.1 NacosConfigService
NacosConfigService 构造函数。
public class NacosConfigService implements ConfigService {
private static final long POST_TIMEOUT = 3000L;
private static final String EMPTY = "";
// Http请求代理
private HttpAgent agent;
// 长轮询
private ClientWorker worker;
private String namespace;
private String encode;
// 创建一个 配置过滤器链管理器
private ConfigFilterChainManager configFilterChainManager = new ConfigFilterChainManager();
public NacosConfigService(Properties properties) throws NacosException {
String encodeTmp = properties.getProperty(PropertyKeyConst.ENCODE);
if (StringUtils.isBlank(encodeTmp)) {
encode = Constants.ENCODE;
} else {
encode = encodeTmp.trim();
}
// 初始化 namespace
initNamespace(properties);
// 创建一个Http通信代理类
agent = new MetricsHttpAgent(new ServerHttpAgent(properties));
agent.start();
// 创建客户端工作对象：长轮询机制
worker = new ClientWorker(agent, configFilterChainManager, properties);
}
}
2.1.2 ClientWorker
ClientWorker 是Nacos中长轮询机制的实现类。
public class ClientWorker implements Closeable {
public ClientWorker(final HttpAgent agent, final ConfigFilterChainManager configFilterChainManager, final Properties properties) {
this.agent = agent;
this.configFilterChainManager = configFilterChainManager;
// 根据 properties 初始化 ClientWorker 属性
init(properties);
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;
}
});
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;
}
});
// 执行配置信息检查
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);
}
// 配置信息检查
public void checkConfigInfo() {
// 分任：分批处理
int listenerSize = cacheMap.get().size();
// 向上取整为批数
int longingTaskCount = (int) Math.ceil(listenerSize / ParamUtil.getPerTaskConfigSize());
if (longingTaskCount > currentLongingTaskCount) {
for (int i = (int) currentLongingTaskCount; i < longingTaskCount; i++) {
/****************长轮询************/
executorService.execute(new LongPollingRunnable(i));
}
currentLongingTaskCount = longingTaskCount;
}
}
// 根据 properties 初始化 ClientWorker 属性
private void init(Properties properties) {
// 请求超时时间：默认30s，可通过配置文件指定(configLongPollTimeout)，最小10s
timeout = Math.max(ConvertUtils.toInt(properties.getProperty(PropertyKeyConst.CONFIG_LONG_POLL_TIMEOUT),
Constants.CONFIG_LONG_POLL_TIMEOUT), Constants.MIN_CONFIG_LONG_POLL_TIMEOUT);
// 任务异常后，重试时间，默认2秒
taskPenaltyTime = ConvertUtils
.toInt(properties.getProperty(PropertyKeyConst.CONFIG_RETRY_TIME), Constants.CONFIG_RETRY_TIME);
// 是否开启远程信息同步
this.enableRemoteSyncConfig = Boolean
.parseBoolean(properties.getProperty(PropertyKeyConst.ENABLE_REMOTE_SYNC_CONFIG));
}
}
2.2 configService
nacos 配置中心提供了一个核心API接口，ConfigService。
public interface ConfigService {
// 获取配置
String getConfig(String dataId, String group, long timeoutMs) throws NacosException;
// 获取配置并注册监听器。
String getConfigAndSignListener(String dataId, String group, long timeoutMs, Listener listener)
throws NacosException;
// 添加监听
void addListener(String dataId, String group, Listener listener) throws NacosException;
// 发布配置
boolean publishConfig(String dataId, String group, String content) throws NacosException;
// 发布配置
boolean publishConfig(String dataId, String group, String content, String type) throws NacosException;
// 发布配置，附带md5值
boolean publishConfigCas(String dataId, String group, String content, String casMd5) throws NacosException;
// 发布配置，附带md5值
boolean publishConfigCas(String dataId, String group, String content, String casMd5, String type)
throws NacosException;
// 删除配置
boolean removeConfig(String dataId, String group) throws NacosException;
// 删除监听
void removeListener(String dataId, String group, Listener listener);
// 获取服务端状态
String getServerStatus();
// 停机
void shutDown() throws NacosException;
}
2.2.1 configService.getConfig(String dataId, String group, long timeoutMs)
configService.getConfig(String dataId, String group, long timeoutMs) 用于获取配置，附带请求超时时间。
public class NacosConfigService implements ConfigService {
@Override
public String getConfig(String dataId, String group, long timeoutMs) throws NacosException {
return getConfigInner(namespace, dataId, group, timeoutMs);
}
private String getConfigInner(String tenant, String dataId, String group, long timeoutMs) throws NacosException {
// 如果group为空，设置为默认分组 DEFAULT_GROUP
group = null2defaultGroup(group);
ParamUtils.checkKeyParam(dataId, group);
ConfigResponse cr = new ConfigResponse();
cr.setDataId(dataId);
cr.setTenant(tenant);
cr.setGroup(group);
// use local config first
// 首先从获取本地配置：读取本地配置文件
String content = LocalConfigInfoProcessor.getFailover(agent.getName(), dataId, group, tenant);
if (content != null) {
LOGGER.warn("[{}] [get-config] get failover ok, dataId={}, group={}, tenant={}, config={}", agent.getName(),
dataId, group, tenant, ContentUtils.truncateContent(content));
cr.setContent(content);
configFilterChainManager.doFilter(null, cr);
content = cr.getContent();
return content;
}
// 本地缓存不存在
try {
// 从nacos服务端获取配置
content = worker.getServerConfig(dataId, group, tenant, timeoutMs);
cr.setContent(content);
// 过滤
configFilterChainManager.doFilter(null, cr);
content = cr.getContent();
return content;
} catch (NacosException ioe) {
if (NacosException.NO_RIGHT == ioe.getErrCode()) {
throw ioe;
}
LOGGER.warn("[{}] [get-config] get from server error, dataId={}, group={}, tenant={}, msg={}",
agent.getName(), dataId, group, tenant, ioe.toString());
}
LOGGER.warn("[{}] [get-config] get snapshot ok, dataId={}, group={}, tenant={}, config={}", agent.getName(),
dataId, group, tenant, ContentUtils.truncateContent(content));
// 本地文件、远程服务都获取不到，读取快照文件配置
content = LocalConfigInfoProcessor.getSnapshot(agent.getName(), dataId, group, tenant);
cr.setContent(content);
configFilterChainManager.doFilter(null, cr);
content = cr.getContent();
return content;
}
}
从本地文件获取配置
String content = LocalConfigInfoProcessor.getFailover(agent.getName(), dataId, group, tenant);
public class LocalConfigInfoProcessor {
public static String getFailover(String serverName, String dataId, String group, String tenant) {
// 获取本地配置文件：./user.home/nacos/config/serverName_nacos
File localPath = getFailoverFile(serverName, dataId, group, tenant);
if (!localPath.exists() || !localPath.isFile()) {
return null;
}
try {
// 读取文件内容
return readFile(localPath);
} catch (IOException ioe) {
LOGGER.error("[" + serverName + "] get failover error, " + localPath, ioe);
return null;
}
}
// 获取故障转移文件
static File getFailoverFile(String serverName, String dataId, String group, String tenant) {
File tmp = new File(LOCAL_SNAPSHOT_PATH, serverName + SUFFIX);
tmp = new File(tmp, FAILOVER_FILE_CHILD_1);
if (StringUtils.isBlank(tenant)) {
tmp = new File(tmp, FAILOVER_FILE_CHILD_2);
} else {
tmp = new File(tmp, FAILOVER_FILE_CHILD_3);
tmp = new File(tmp, tenant);
}
return new File(new File(tmp, group), dataId);
}
}
从Nacos服务器获取配置
ConfigResponse response = worker.getServerConfig(dataId, group, tenant, timeoutMs, false);
调用 ClientWorker 中的 getServerConfig 方法。
public class ClientWorker implements Closeable {
public String getServerConfig(String dataId, String group, String tenant, long readTimeout)
throws NacosException {
if (StringUtils.isBlank(group)) {
// 使用默认分组
group = Constants.DEFAULT_GROUP;
}
HttpResult result = null;
try {
List<String> params = null;
if (StringUtils.isBlank(tenant)) {
params = Arrays.asList("dataId", dataId, "group", group);
} else {
params = Arrays.asList("dataId", dataId, "group", group, "tenant", tenant);
}
// 发送Get请求：/v1/cs/configs
result = agent.httpGet(Constants.CONFIG_CONTROLLER_PATH, null, params, agent.getEncode(), readTimeout);
} catch (IOException e) {
String message = String.format(
"[%s] [sub-server] get server config exception, dataId=%s, group=%s, tenant=%s", agent.getName(),
dataId, group, tenant);
LOGGER.error(message, e);
throw new NacosException(NacosException.SERVER_ERROR, e);
}
switch (result.code) {
case HttpURLConnection.HTTP_OK:
// 更新本地快照信息
LocalConfigInfoProcessor.saveSnapshot(agent.getName(), dataId, group, tenant, result.content);
return result.content;
case HttpURLConnection.HTTP_NOT_FOUND:
// 更新本地快照信息
LocalConfigInfoProcessor.saveSnapshot(agent.getName(), dataId, group, tenant, null);
return null;
case HttpURLConnection.HTTP_CONFLICT: {
LOGGER.error(
"[{}] [sub-server-error] get server config being modified concurrently, dataId={}, group={}, "
+ "tenant={}", agent.getName(), dataId, group, tenant);
throw new NacosException(NacosException.CONFLICT,
"data being modified, dataId=" + dataId + ",group=" + group + ",tenant=" + tenant);
}
case HttpURLConnection.HTTP_FORBIDDEN: {
LOGGER.error("[{}] [sub-server-error] no right, dataId={}, group={}, tenant={}", agent.getName(), dataId,
group, tenant);
throw new NacosException(result.code, result.content);
}
default: {
LOGGER.error("[{}] [sub-server-error] dataId={}, group={}, tenant={}, code={}", agent.getName(), dataId,
group, tenant, result.code);
throw new NacosException(result.code,
"http error, code=" + result.code + ",dataId=" + dataId + ",group=" + group + ",tenant=" + tenant);
}
}
}
}
2.2.2 configService.addListener(String dataId, String group, Listener listener)
configService.addListener(String dataId, String group, Listener listener) 用于给当前dataId、group的配置，添加一个事件监听，用于配置发生变更后，进行通知处理。
public class NacosConfigService implements ConfigService {
@Override
public void addListener(String dataId, String group, Listener listener) throws NacosException {
worker.addTenantListeners(dataId, group, Arrays.asList(listener));
}
}
NacosConfigService 中的 addListener(String dataId, String group, Listener listener) 最终会调用 ClientWorker 中的 addTenantListeners(String dataId, String group, List<? extends Listener> listeners) 方法
public class ClientWorker {
public void addTenantListeners(String dataId, String group, List<? extends Listener> listeners) throws NacosException {
// 如果group为空，设置默认分组DEFAULT_GROUP
group = null2defaultGroup(group);
String tenant = agent.getTenant();
// 如果不存在则添加缓存数据
CacheData cache = addCacheDataIfAbsent(dataId, group, tenant);
for (Listener listener : listeners) {
// 添加监听
cache.addListener(listener);
}
}
// 如果不存在则添加缓存数据
public CacheData addCacheDataIfAbsent(String dataId, String group, String tenant) throws NacosException {
// 获取缓存
CacheData cache = getCache(dataId, group, tenant);
if (null != cache) {
// 不为空，直接return
return cache;
}
String key = GroupKey.getKeyTenant(dataId, group, tenant);
synchronized (cacheMap) {// 加锁，线程安全性
CacheData cacheFromMap = getCache(dataId, group, tenant);
// multiple listeners on the same dataid+group and race condition,so
// double check again
// other listener thread beat me to set to cacheMap
// 双重检查机制
if (null != cacheFromMap) {
cache = cacheFromMap;
// reset so that server not hang this check
cache.setInitializing(true);
} else {
// 不存在，创建缓存对象
cache = new CacheData(configFilterChainManager, agent.getName(), dataId, group, tenant);
// fix issue # 1317
// 是否开启远程同步
if (enableRemoteSyncConfig) {
// 获取配置
String content = getServerConfig(dataId, group, tenant, 3000L);
cache.setContent(content);
}
}
// 设置缓存
Map<String, CacheData> copy = new HashMap<String, CacheData>(cacheMap.get());
copy.put(key, cache);
cacheMap.set(copy);
}
LOGGER.info("[{}] [subscribe] {}", agent.getName(), key);
MetricsMonitor.getListenConfigCountMonitor().set(cacheMap.get().size());
return cache;
}
}
2.3 长轮询机制
在探讨Nacos长轮询机制前，先给大家普及一下几个概念：
- 短轮询：指客户端每隔一段时间向服务器发起一次Http请求，服务端收到请求后，进行处理，然后返回给客户端。
- 长轮询：指客户端向服务端发起一个带**超时时间(timeout)**的Http请求，并在Http连接超时前，不主动断开连接，需要服务端主动回写数据，否则将一直重复以上过程。
Nacos就是利用了长轮询机制，客户端会开启一个线程，不断向服务端发起一个配置是否存在变更的请求(30s超时)，服务端收到请求后，如果配置不存在变更，并不会立即返回，而是当配置发生变更后，主动是否将消息回写给客户端。
客户端会存在两种情况：
- 请求超时：无配置变更，开启下一次轮询请求
- 服务器返回数据：解析服务器返回数据，通过Nameserver、dataId、group重新回去服务器配置，更新本地缓存，触发事件监听，开启下一次轮询请求。
Nacos长轮询原理，分为了客户端 和 服务端，核心代码如下：
2.3 客户端 LongPollingRunnable
LongPollingRunnable 为 ClientWorker 中的一个内部类，代码如下：
public class ClientWorker {
// 检查配置信息：分批处理，一次最多3000
public void checkConfigInfo() {
// 分任务
int listenerSize = cacheMap.get().size();
// 向上取整为批数
int longingTaskCount = (int) Math.ceil(listenerSize / ParamUtil.getPerTaskConfigSize());
if (longingTaskCount > currentLongingTaskCount) {
for (int i = (int) currentLongingTaskCount; i < longingTaskCount; i++) {
// 要判断任务是否在执行 这块需要好好想想。 任务列表现在是无序的。变化过程可能有问题
// i 为当前批次，用于筛选过滤出属于当前批次的cacheData
executorService.execute(new LongPollingRunnable(i));
}
currentLongingTaskCount = longingTaskCount;
}
}
class LongPollingRunnable implements Runnable {
// 当前批次id，用于筛选过滤出属于当前批次的cacheData
private 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
// 获取属于当前批次的cacheData
for (CacheData cacheData : cacheMap.get().values()) {
if (cacheData.getTaskId() == taskId) {
cacheDatas.add(cacheData);
try {
// 检查本地配置
checkLocalConfig(cacheData);
if (cacheData.isUseLocalConfigInfo()) { // 使用本地配置信息
// 检查cacheData和内存缓存文件是否不一致，如果不一致，通知所有Listener
cacheData.checkListenerMd5();
}
} catch (Exception e) {
LOGGER.error("get local config info error", e);
}
}
}
// check server config
// 长轮询：将当前批次的所有cacheData通过Http请求发送给服务端，并附带30s超时时间
// 1.服务端数据无变化，请求超时，changedGroupKeys = Collections.emptyList()
// 2.服务端数据存在变更，循环遍历，通过getServerConfig获取并更新本地缓存，触发事件监听
List<String> changedGroupKeys = checkUpdateDataIds(cacheDatas, inInitializingCacheList);
// 遍历发送变更的groupKey
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 {
// 重新获取服务端配置，本更新本地配置文件缓存内容
String content = getServerConfig(dataId, group, tenant, 3000L);
// 更新本地内存配置
CacheData cache = cacheMap.get().get(GroupKey.getKeyTenant(dataId, group, tenant));
cache.setContent(content);
LOGGER.info("[{}] [data-received] dataId={}, group={}, tenant={}, md5={}, content={}",
agent.getName(), dataId, group, tenant, cache.getMd5(),
ContentUtils.truncateContent(content));
} 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);
}
}
// 遍历cacheDatas，判断是否需要重新初始化本地文件缓存
for (CacheData cacheData : cacheDatas) {
if (!cacheData.isInitializing() || inInitializingCacheList
.contains(GroupKey.getKeyTenant(cacheData.dataId, cacheData.group, cacheData.tenant))) {
// 检查cacheData和内存缓存文件是否不一致，如果不一致，通知所有Listener
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);
// 如果发生异常，延迟taskPenaltyTime后执行当前任务
executorService.schedule(this, taskPenaltyTime, TimeUnit.MILLISECONDS);
}
}
}
/**
* 从Server获取值变化了的DataID列表。返回的对象里只有dataId和group是有效的。 保证不返回NULL。
*/
List<String> checkUpdateDataIds(List<CacheData> cacheDatas, List<String> inInitializingCacheList) throws IOException {
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()) {
// cacheData 首次出现在cacheMap中&首次check更新
inInitializingCacheList
.add(GroupKey.getKeyTenant(cacheData.dataId, cacheData.group, cacheData.tenant));
}
}
}
boolean isInitializingCacheList = !inInitializingCacheList.isEmpty();
// 检查更新配置字符串
return checkUpdateConfigStr(sb.toString(), isInitializingCacheList);
}
/**
* 从Server获取值变化了的DataID列表。返回的对象里只有dataId和group是有效的。 保证不返回NULL。
*/
List<String> checkUpdateConfigStr(String probeUpdateString, boolean isInitializingCacheList) throws IOException {
List<String> params = Arrays.asList(Constants.PROBE_MODIFY_REQUEST, probeUpdateString);
List<String> headers = new ArrayList<String>(2);
headers.add("Long-Pulling-Timeout");
// 设置超时时间，默认30s
headers.add("" + timeout);
// told server do not hang me up if new initializing cacheData added in
// 是否初始化缓存列表
if (isInitializingCacheList) {
headers.add("Long-Pulling-Timeout-No-Hangup");
headers.add("true");
}
// 为空，直接return
if (StringUtils.isBlank(probeUpdateString)) {
return Collections.emptyList();
}
try {
// 发送带超时时间的Http请求，请求路径：/v1/cs/configs/listener
HttpResult result = agent.httpPost(Constants.CONFIG_CONTROLLER_PATH + "/listener", headers, params,
agent.getEncode(), timeout);
if (HttpURLConnection.HTTP_OK == result.code) {
setHealthServer(true);
// 解析更新数据 ID 响应
return parseUpdateDataIdResponse(result.content);
} else {
setHealthServer(false);
LOGGER.error("[{}] [check-update] get changed dataId error, code: {}", agent.getName(), result.code);
}
} catch (IOException e) {
setHealthServer(false);
LOGGER.error("[" + agent.getName() + "] [check-update] get changed dataId exception", e);
throw e;
}
// 超时返回 Collections.emptyList()
return Collections.emptyList();
}
// 检查本地配置
private void checkLocalConfig(CacheData cacheData) {
final String dataId = cacheData.dataId;
final String group = cacheData.group;
final String tenant = cacheData.tenant;
File path = LocalConfigInfoProcessor.getFailoverFile(agent.getName(), dataId, group, tenant);
// 没有 -> 有
if (!cacheData.isUseLocalConfigInfo() && path.exists()) {
String content = LocalConfigInfoProcessor.getFailover(agent.getName(), dataId, group, tenant);
String md5 = MD5.getInstance().getMD5String(content);
cacheData.setUseLocalConfigInfo(true);
cacheData.setLocalConfigInfoVersion(path.lastModified());
cacheData.setContent(content);
LOGGER.warn("[{}] [failover-change] failover file created. dataId={}, group={}, tenant={}, md5={}, content={}",
agent.getName(), dataId, group, tenant, md5, ContentUtils.truncateContent(content));
return;
}
// 有 -> 没有。不通知业务监听器，从server拿到配置后通知。
if (cacheData.isUseLocalConfigInfo() && !path.exists()) {
cacheData.setUseLocalConfigInfo(false);
LOGGER.warn("[{}] [failover-change] failover file deleted. dataId={}, group={}, tenant={}", agent.getName(),
dataId, group, tenant);
return;
}
// 有变更
if (cacheData.isUseLocalConfigInfo() && path.exists()
&& cacheData.getLocalConfigInfoVersion() != path.lastModified()) {
String content = LocalConfigInfoProcessor.getFailover(agent.getName(), dataId, group, tenant);
String md5 = MD5.getInstance().getMD5String(content);
cacheData.setUseLocalConfigInfo(true);
cacheData.setLocalConfigInfoVersion(path.lastModified());
cacheData.setContent(content);
LOGGER.warn("[{}] [failover-change] failover file changed. dataId={}, group={}, tenant={}, md5={}, content={}",
agent.getName(), dataId, group, tenant, md5, ContentUtils.truncateContent(content));
}
}
}
2.4 服务端
由上面客户端代码分析可知，客户端会发送一个 /v1/cs/configs/listener 的请求。
// 发送带超时时间的Http请求，请求路径：/v1/cs/configs/listener
HttpResult result = agent.httpPost(Constants.CONFIG_CONTROLLER_PATH + "/listener", headers, params,
agent.getEncode(), timeout);
服务端收到请求后，处理如下：
@Controller
// Constants.CONFIG_CONTROLLER_PATH = /v1/cs/configs
@RequestMapping(Constants.CONFIG_CONTROLLER_PATH)
public class ConfigController {
/**
* 比较MD5
*/
@RequestMapping(value = "/listener", method = RequestMethod.POST)
public void listener(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
request.setAttribute("org.apache.catalina.ASYNC_SUPPORTED", true);
// 获取需要比较的字符串
String probeModify = request.getParameter("Listening-Configs");
if (StringUtils.isBlank(probeModify)) {
throw new IllegalArgumentException("invalid probeModify");
}
// 解码
probeModify = URLDecoder.decode(probeModify, Constants.ENCODE);
// key -> groupKey value -> md5
Map<String, String> clientMd5Map;
try {
// 获取客户端传输过来的md5值
clientMd5Map = MD5Util.getClientMd5Map(probeModify);
} catch (Throwable e) {
throw new IllegalArgumentException("invalid probeModify");
}
// do long-polling
// 长轮询
inner.doPollingConfig(request, response, clientMd5Map, probeModify.length());
}
}
2.4.1 ConfigServletInner.doPollingConfig
@Service
public class ConfigServletInner {
/**
* 轮询接口
*/
public String doPollingConfig(HttpServletRequest request, HttpServletResponse response,
Map<String, String> clientMd5Map, int probeRequestSize)
throws IOException, ServletException {
// 长轮询
if (LongPollingService.isSupportLongPolling(request)) {
// 添加长轮询客户端
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 + "";
}
}
2.4.2 LongPollingService.addLongPollingClient
@Service
public class LongPollingService extends AbstractEventListener {
public void addLongPollingClient(HttpServletRequest req, HttpServletResponse rsp, Map<String, String> clientMd5Map,
int probeRequestSize) {
// 获取客户端超时时间
String str = req.getHeader(LongPollingService.LONG_POLLING_HEADER);
// 挂断标志
String noHangUpFlag = req.getHeader(LongPollingService.LONG_POLLING_NO_HANG_UP_HEADER);
// 应用名称
String appName = req.getHeader(RequestUtil.CLIENT_APPNAME_HEADER);
String tag = req.getHeader("Vipserver-Tag");
// 延迟时间，服务端处理时间。0.5s
int delayTime = SwitchService.getSwitchInteger(SwitchService.FIXED_DELAY_TIME, 500);
/**
* 提前500ms返回响应，为避免客户端超时
*/
long timeout = Math.max(10000, Long.parseLong(str) - delayTime);
if (isFixedPolling()) {
timeout = Math.max(10000, getFixedPollingInterval());
// do nothing but set fix polling timeout
} else {
// 先检查是否存在变更，如果存在，直接返回
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;
}
}
/*************************不存在变更，采用servlet 3.0 异步处理***************************/
// 客户端ip
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);
// 开启定时任务
// 其中，timeout = Math.max(10000, Long.parseLong(str) - delayTime) = Math.max(10000, 30000 - 500) = 29.5s
scheduler.execute(
new ClientLongPolling(asyncContext, clientMd5Map, ip, probeRequestSize, timeout, appName, tag));
}
}
2.4.3 ClientLongPolling
ClientLongPolling 为 LongPollingService 的内部类，代码如下：
@Service
public class LongPollingService extends AbstractEventListener {
class ClientLongPolling implements Runnable {
@Override
public void run() {
// 开启一个延时线程，timeoutTime=29.5s
asyncTimeoutFuture = scheduler.schedule(new Runnable() {
@Override
public void run() {
try {
// 获取并设置客户端IP
getRetainIps().put(ClientLongPolling.this.ip, System.currentTimeMillis());
/**
* 删除订阅关系
*/
allSubs.remove(ClientLongPolling.this);
// 是否固定轮询
if (isFixedPolling()) {
LogUtil.clientLog.info("{}|{}|{}|{}|{}|{}",
(System.currentTimeMillis() - createTime),
"fix", RequestUtil.getRemoteIp((HttpServletRequest)asyncContext.getRequest()),
"polling",
clientMd5Map.size(), probeRequestSize);
// 通过md5值，获取当前所有变更的groups
List<String> changedGroups = MD5Util.compareMd5(
(HttpServletRequest)asyncContext.getRequest(),
(HttpServletResponse)asyncContext.getResponse(), clientMd5Map);
if (changedGroups.size() > 0) {
// 发送数据
sendResponse(changedGroups);
} else {
// 发送数据
sendResponse(null);
}
} else {
LogUtil.clientLog.info("{}|{}|{}|{}|{}|{}",
(System.currentTimeMillis() - createTime),
"timeout", RequestUtil.getRemoteIp((HttpServletRequest)asyncContext.getRequest()),
"polling",
clientMd5Map.size(), probeRequestSize);
// 发送数据
sendResponse(null);
}
} catch (Throwable t) {
LogUtil.defaultLog.error("long polling error:" + t.getMessage(), t.getCause());
}
}
}, timeoutTime, TimeUnit.MILLISECONDS);
// 添加订阅关系
allSubs.add(this);
}
void sendResponse(List<String> changedGroups) {
/**
* 取消超时任务
*/
if (null != asyncTimeoutFuture) {
asyncTimeoutFuture.cancel(false);
}
generateResponse(changedGroups);
}
void generateResponse(List<String> changedGroups) {
if (null == changedGroups) {
/**
* 告诉容器发送HTTP响应
*/
asyncContext.complete();
return;
}
HttpServletResponse response = (HttpServletResponse)asyncContext.getResponse();
try {
// 获取resp
String respString = MD5Util.compareMd5ResultString(changedGroups);
// 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);
// 回写数据
response.getWriter().println(respString);
asyncContext.complete();
} catch (Exception se) {
pullLog.error(se.toString(), se);
asyncContext.complete();
}
}
}
}
注意：如果在29.5s内发生变化，那么nacos是怎么处理的呢？
假如，在这29.5s内，你进入了nacos控制台，修改配置内容后，保存发布，那这个时候，nacos服务端会做哪些内容呢？？
2.4.4 LocalDataChangeEvent
通过浏览器控制台可发现，当你点击保存后，会调用nacos服务端的 /v1/cs/configs/ 请求，最后发送一个 LocalDataChangeEvent 事件。
@Service
public class LongPollingService extends AbstractEventListener {
/**
* 长轮询订阅关系
*/
final Queue<ClientLongPolling> allSubs;
@Override
public void onEvent(Event event) {
if (isFixedPolling()) {
// ignore
} else {
if (event instanceof LocalDataChangeEvent) {
// 接收 LocalDataChangeEvent
LocalDataChangeEvent evt = (LocalDataChangeEvent)event;
// 执行 DataChangeTask
scheduler.execute(new DataChangeTask(evt.groupKey, evt.isBeta, evt.betaIps));
}
}
}
class DataChangeTask implements Runnable {
@Override
public void run() {
try {
ConfigService.getContentBetaMd5(groupKey);
// 循环遍历 allSubs Queue<ClientLongPolling> allSubs;
for (Iterator<ClientLongPolling> iter = allSubs.iterator(); iter.hasNext(); ) {
ClientLongPolling clientSub = iter.next();
// 如果当前 ClientLongPolling 中的 clientMd5Map key中存在当前 groupKey，则进行通知
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());
// 删除订阅关系
iter.remove();
LogUtil.clientLog.info("{}|{}|{}|{}|{}|{}|{}",
(System.currentTimeMillis() - changeTime),
"in-advance",
RequestUtil.getRemoteIp((HttpServletRequest)clientSub.asyncContext.getRequest()),
"polling",
clientSub.clientMd5Map.size(), clientSub.probeRequestSize, groupKey);
// 发送服务配置变更groupKey，完成实时通知
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;
}
}
至此，Nacos 配置中心原理分析完成，下面我们回顾一下整体流程。
