nacos的服务发现主要采用服务端主动推送+客户端定时拉取；心跳机制通过每5s向服务端发送心跳任务来保活，当超过15s服务端未接收到心跳任务时，将该实例设置为非健康状态；当超过30s时，删除该实例。
1.服务发现
nacos主要采用服务端主动推送+客户端定时拉取来保证AP架构的高可用性。
NacosNamingService：服务发现的接口（客户端！）
每个nacos实例有本地缓存Map，存放所有的实例
调用查询服务实例列表
/nacos`/v1/ns/instance/list
NacosNamingService.getAllInstances() -> getServiceInfo()
核心方法是getServiceInfo，代码如下：
java
public ServiceInfo getServiceInfo(final String serviceName, final String clusters) {
NAMING_LOGGER.debug("failover-mode: " + failoverReactor.isFailoverSwitch());
String key = ServiceInfo.getKey(serviceName, clusters);
if (failoverReactor.isFailoverSwitch()) {
return failoverReactor.getService(key);
}
ServiceInfo serviceObj = getServiceInfo0(serviceName, clusters);// 从本地拿实例
if (null == serviceObj) {// 如果拿到为空，则更新服务列表
serviceObj = new ServiceInfo(serviceName, clusters);
serviceInfoMap.put(serviceObj.getKey(), serviceObj);
updatingMap.put(serviceName, new Object());
updateServiceNow(serviceName, clusters);
updatingMap.remove(serviceName);
} else if (updatingMap.containsKey(serviceName)) {
if (UPDATE_HOLD_INTERVAL > 0) {
// hold a moment waiting for update finish
synchronized (serviceObj) {
try {
serviceObj.wait(UPDATE_HOLD_INTERVAL);
} catch (InterruptedException e) {
NAMING_LOGGER
.error("[getServiceInfo] serviceName:" + serviceName + ", clusters:" + clusters, e);
}
}
}
}
scheduleUpdateIfAbsent(serviceName, clusters);// 定时拉取
return serviceInfoMap.get(serviceObj.getKey());// 从map拿
}本地从服务端拉取服务实例，放到本地缓存中
java
public String queryList(String serviceName, String clusters, int udpPort, boolean healthyOnly)
throws NacosException {
final Map<String, String> params = new HashMap<String, String>(8);
params.put(CommonParams.NAMESPACE_ID, namespaceId);
params.put(CommonParams.SERVICE_NAME, serviceName);
params.put("clusters", clusters);
params.put("udpPort", String.valueOf(udpPort));
params.put("clientIP", NetUtils.localIP());
params.put("healthyOnly", String.valueOf(healthyOnly));
return reqApi(UtilAndComs.nacosUrlBase + "/instance/list", params, HttpMethod.GET);// 调用接口
}客户端通过定时任务-->定时拉取服务端的实例，更新本地缓存（在发起服务调用的时候，才会执行定时任务！）
java
public void scheduleUpdateIfAbsent(String serviceName, String clusters) {
if (futureMap.get(ServiceInfo.getKey(serviceName, clusters)) != null) {
return;
}
synchronized (futureMap) {
if (futureMap.get(ServiceInfo.getKey(serviceName, clusters)) != null) {
return;
}
ScheduledFuture<?> future = addTask(new UpdateTask(serviceName, clusters));
futureMap.put(ServiceInfo.getKey(serviceName, clusters), future);
}
}2.心跳机制
NamingService->register
注册实例的时候，客户端会有一个心跳任务，定时5s向服务端发送心跳！
executorService.schedule(new BeatTask(beatInfo), beatInfo.getPeriod(), TimeUnit.MILLISECONDS);
BeatTask就是心跳任务
调用Instance/beat接口，发送实例心跳检查
BeatTask#run的代码如下：
java
@Override
public void run() {
if (beatInfo.isStopped()) {
return;
}
long nextTime = beatInfo.getPeriod();
try {
JsonNode result = serverProxy.sendBeat(beatInfo, BeatReactor.this.lightBeatEnabled);
long interval = result.get("clientBeatInterval").asLong();
boolean lightBeatEnabled = false;
if (result.has(CommonParams.LIGHT_BEAT_ENABLED)) {
lightBeatEnabled = result.get(CommonParams.LIGHT_BEAT_ENABLED).asBoolean();
}
BeatReactor.this.lightBeatEnabled = lightBeatEnabled;
if (interval > 0) {
nextTime = interval;
}
int code = NamingResponseCode.OK;
if (result.has(CommonParams.CODE)) {
code = result.get(CommonParams.CODE).asInt();
}
if (code == NamingResponseCode.RESOURCE_NOT_FOUND) {
Instance instance = new Instance();
instance.setPort(beatInfo.getPort());
instance.setIp(beatInfo.getIp());
instance.setWeight(beatInfo.getWeight());
instance.setMetadata(beatInfo.getMetadata());
instance.setClusterName(beatInfo.getCluster());
instance.setServiceName(beatInfo.getServiceName());
instance.setInstanceId(instance.getInstanceId());
instance.setEphemeral(true);
try {
serverProxy.registerService(beatInfo.getServiceName(),
NamingUtils.getGroupName(beatInfo.getServiceName()), instance);
} catch (Exception ignore) {
}
}
} catch (NacosException ex) {
NAMING_LOGGER.warn("[CLIENT-BEAT] failed to send beat: {}, code: {}, msg: {}",
JacksonUtils.toJson(beatInfo), ex.getErrCode(), ex.getErrMsg());
} catch (Exception unknownEx) {
NAMING_LOGGER.error("[CLIENT-BEAT] failed to send beat: {}, unknown exception msg: {}",
JacksonUtils.toJson(beatInfo), unknownEx.getMessage(), unknownEx);
} finally {
executorService.schedule(new BeatTask(beatInfo), nextTime, TimeUnit.MILLISECONDS);// 定时任务
}
}服务端会更新心跳的时间！每隔5秒检查一下实例健康状态
对于集群而言，在一台服务端执行定时任务即可！不需要再所有节点都执行定时任务
当实例下线后，服务端通过InstanceController，检查健康状态（健康任务检查）。代码入口：
createEmptyService->createServiceIfAbsent->putServiceAndInit->init->scheduleCheck（定时任务）
if (System.currentTimeMillis() - instance.getLastBeat() > instance.getInstanceHeartBeatTimeOut()) {// 心跳时间判断
如果超过15秒，设置实例为非健康（更新健康状态）
if (System.currentTimeMillis() - instance.getLastBeat() > instance.getIpDeleteTimeout()) {// 如果已经过去了30s，直接删掉这个机器（删除实例）
asyncHttpRequest(url, headers, paramValues, callback, HttpMethod.DELETE);
核心代码如下：
java
@Override
public void run() {
try {
if (!getDistroMapper().responsible(service.getName())) {
return;
}
if (!getSwitchDomain().isHealthCheckEnabled()) {
return;
}
List<Instance> instances = service.allIPs(true);// 获取服务端的所有实例
// first set health status of instances:
for (Instance instance : instances) {
if (System.currentTimeMillis() - instance.getLastBeat() > instance.getInstanceHeartBeatTimeOut()) {// 心跳时间判断
if (!instance.isMarked()) {
if (instance.isHealthy()) {
instance.setHealthy(false);// 如果超过15s，健康设置为false
Loggers.EVT_LOG
.info("{POS} {IP-DISABLED} valid: {}:{}@{}@{}, region: {}, msg: client timeout after {}, last beat: {}",
instance.getIp(), instance.getPort(), instance.getClusterName(),
service.getName(), UtilsAndCommons.LOCALHOST_SITE,
instance.getInstanceHeartBeatTimeOut(), instance.getLastBeat());
getPushService().serviceChanged(service);
ApplicationUtils.publishEvent(new InstanceHeartbeatTimeoutEvent(this, instance));
}
}
}
}
if (!getGlobalConfig().isExpireInstance()) {
return;
}
// then remove obsolete instances:
for (Instance instance : instances) {
if (instance.isMarked()) {
continue;
}
if (System.currentTimeMillis() - instance.getLastBeat() > instance.getIpDeleteTimeout()) {
// delete instance
Loggers.SRV_LOG.info("[AUTO-DELETE-IP] service: {}, ip: {}", service.getName(),
JacksonUtils.toJson(instance));
deleteIp(instance);
}
}
} catch (Exception e) {
Loggers.SRV_LOG.warn("Exception while processing client beat time out.", e);
}
}3.服务事件变动
客户端每隔5秒从服务端拉取一次信息，是不是有延迟！
对于AP架构而言，有一点延迟 无所谓。Ribbon会进行重试
当服务端的服务列表变化时，服务端会主动推送给客户端信息
核心代码入口：notifier#run->handle->onChange
onChange更新注册表的相关代码！
getPushService().serviceChanged(this);// 发布 服务变化 的事件，通知客户端
java
public void updateIPs(Collection<Instance> instances, boolean ephemeral) {
Map<String, List<Instance>> ipMap = new HashMap<>(clusterMap.size());
for (String clusterName : clusterMap.keySet()) {
ipMap.put(clusterName, new ArrayList<>());
}
for (Instance instance : instances) {
try {
if (instance == null) {
Loggers.SRV_LOG.error("[NACOS-DOM] received malformed ip: null");
continue;
}
if (StringUtils.isEmpty(instance.getClusterName())) {
instance.setClusterName(UtilsAndCommons.DEFAULT_CLUSTER_NAME);
}
if (!clusterMap.containsKey(instance.getClusterName())) {
Loggers.SRV_LOG
.warn("cluster: {} not found, ip: {}, will create new cluster with default configuration.",
instance.getClusterName(), instance.toJson());
Cluster cluster = new Cluster(instance.getClusterName(), this);
cluster.init();
getClusterMap().put(instance.getClusterName(), cluster);
}
List<Instance> clusterIPs = ipMap.get(instance.getClusterName());
if (clusterIPs == null) {
clusterIPs = new LinkedList<>();
ipMap.put(instance.getClusterName(), clusterIPs);
}
clusterIPs.add(instance);
} catch (Exception e) {
Loggers.SRV_LOG.error("[NACOS-DOM] failed to process ip: " + instance, e);
}
}
for (Map.Entry<String, List<Instance>> entry : ipMap.entrySet()) {
//make every ip mine
List<Instance> entryIPs = entry.getValue();
clusterMap.get(entry.getKey()).updateIps(entryIPs, ephemeral);// 核心注册逻辑
}
setLastModifiedMillis(System.currentTimeMillis());
getPushService().serviceChanged(this);// 发布 服务变化 的事件
StringBuilder stringBuilder = new StringBuilder();
for (Instance instance : allIPs()) {
stringBuilder.append(instance.toIpAddr()).append("_").append(instance.isHealthy()).append(",");
}
Loggers.EVT_LOG.info("[IP-UPDATED] namespace: {}, service: {}, ips: {}", getNamespaceId(), getName(),
stringBuilder.toString());
}（通过全文搜索事件，找到这个方法）PushService#onApplicationEvent，它来处理事件。代码如下：
udpPush(ackEntry);// 服务端给客户端发送udp信息，通知客户端实例变动
java
@Override
public void onApplicationEvent(ServiceChangeEvent event) {
Service service = event.getService();
String serviceName = service.getName();
String namespaceId = service.getNamespaceId();
Future future = GlobalExecutor.scheduleUdpSender(() -> {
try {
Loggers.PUSH.info(serviceName + " is changed, add it to push queue.");
ConcurrentMap<String, PushClient> clients = clientMap
.get(UtilsAndCommons.assembleFullServiceName(namespaceId, serviceName));
if (MapUtils.isEmpty(clients)) {
return;
}
Map<String, Object> cache = new HashMap<>(16);
long lastRefTime = System.nanoTime();
for (PushClient client : clients.values()) {
if (client.zombie()) {
Loggers.PUSH.debug("client is zombie: " + client.toString());
clients.remove(client.toString());
Loggers.PUSH.debug("client is zombie: " + client.toString());
continue;
}
Receiver.AckEntry ackEntry;
Loggers.PUSH.debug("push serviceName: {} to client: {}", serviceName, client.toString());
String key = getPushCacheKey(serviceName, client.getIp(), client.getAgent());
byte[] compressData = null;
Map<String, Object> data = null;
if (switchDomain.getDefaultPushCacheMillis() >= 20000 && cache.containsKey(key)) {
org.javatuples.Pair pair = (org.javatuples.Pair) cache.get(key);
compressData = (byte[]) (pair.getValue0());
data = (Map<String, Object>) pair.getValue1();
Loggers.PUSH.debug("[PUSH-CACHE] cache hit: {}:{}", serviceName, client.getAddrStr());
}
if (compressData != null) {
ackEntry = prepareAckEntry(client, compressData, data, lastRefTime);
} else {
ackEntry = prepareAckEntry(client, prepareHostsData(client), lastRefTime);
if (ackEntry != null) {
cache.put(key, new org.javatuples.Pair<>(ackEntry.origin.getData(), ackEntry.data));
}
}
Loggers.PUSH.info("serviceName: {} changed, schedule push for: {}, agent: {}, key: {}",
client.getServiceName(), client.getAddrStr(), client.getAgent(),
(ackEntry == null ? null : ackEntry.key));
udpPush(ackEntry);// 给客户端发送udp信息
}
} catch (Exception e) {
Loggers.PUSH.error("[NACOS-PUSH] failed to push serviceName: {} to client, error: {}", serviceName, e);
} finally {
futureMap.remove(UtilsAndCommons.assembleFullServiceName(namespaceId, serviceName));
}
}, 1000, TimeUnit.MILLISECONDS);
futureMap.put(UtilsAndCommons.assembleFullServiceName(namespaceId, serviceName), future);
}客户端接收udp报文的代码如下：
java
public ServiceInfo getServiceInfo(final String serviceName, final String clusters) {
NAMING_LOGGER.debug("failover-mode: " + failoverReactor.isFailoverSwitch());
String key = ServiceInfo.getKey(serviceName, clusters);
if (failoverReactor.isFailoverSwitch()) {
return failoverReactor.getService(key);
}
ServiceInfo serviceObj = getServiceInfo0(serviceName, clusters);// 从本地拿实例
if (null == serviceObj) {// 如果拿到为空，则更新服务列表
serviceObj = new ServiceInfo(serviceName, clusters);
serviceInfoMap.put(serviceObj.getKey(), serviceObj);
updatingMap.put(serviceName, new Object());
updateServiceNow(serviceName, clusters);// upd的端口