Nacos服务发现源码解析

1.Spring服务发现的统一规范

Spring将这套规范定义在Spring Cloud Common中

discovery包下面定义了服务发现的规范

核心接口：DiscoveryClient 用于服务发现

2.Nacos客户端实现服务发现

NacosDiscoveryClient 实现 DiscoveryClient接口。

当nacos客户端运行起来之后，并不会去请求服务信息，只是会去做服务注册，配置获取等。

当第一次请求时候，才会去获取服务，也就是懒加载

1.在本地查找实例缓存信息，如果缓存为空，则开启定时任务请求服务端获取实例信息列表来更新缓存到本地

@Override
public List<ServiceInstance> getInstances(String serviceId) {
    try {
        return serviceDiscovery.getInstances(serviceId);
    }
    ...省略
}
public List<ServiceInstance> getInstances(String serviceId) throws NacosException {
    String group = discoveryProperties.getGroup();
    List<Instance> instances = namingService().selectInstances(serviceId, group, true);
    return hostToServiceInstanceList(instances, serviceId);
}
public List<Instance> selectInstances(String serviceName, String groupName, List<String> clusters, boolean healthy,
        boolean subscribe) throws NacosException {
    ServiceInfo serviceInfo;
    // 默认订阅服务
    if (subscribe) {
        serviceInfo = hostReactor.getServiceInfo(NamingUtils.getGroupedName(serviceName, groupName),
                StringUtils.join(clusters, ","));
    } else {
        serviceInfo = hostReactor
                .getServiceInfoDirectlyFromServer(NamingUtils.getGroupedName(serviceName, groupName),
                        StringUtils.join(clusters, ","));
    }
    return selectInstances(serviceInfo, healthy);
}
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);
    }
    // 本地缓存找
    ServiceInfo serviceObj = getServiceInfo0(serviceName, clusters);
    if (null == serviceObj) {
        serviceObj = new ServiceInfo(serviceName, clusters);
        serviceInfoMap.put(serviceObj.getKey(), serviceObj);
        updatingMap.put(serviceName, new Object());
        // 从服务端拉取服务信息
        updateServiceNow(serviceName, clusters);
        updatingMap.remove(serviceName);
    } else if (updatingMap.containsKey(serviceName)) {
        ...省略
    }
　　 //添加定时任务
    scheduleUpdateIfAbsent(serviceName, clusters);
    return serviceInfoMap.get(serviceObj.getKey());
}
// 更新服务信息
private void updateServiceNow(String serviceName, String clusters) {
    try {
        updateService(serviceName, clusters);
    } catch (NacosException e) {
        NAMING_LOGGER.error("[NA] failed to update serviceName: " + serviceName, e);
    }
}
//如果不存在，则添加定时任务
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;
        }
        //添加定时任务
        ScheduledFuture<?> future = addTask(new UpdateTask(serviceName, clusters));
        futureMap.put(ServiceInfo.getKey(serviceName, clusters), future);
    }
}

// 从服务端拉取服务信息
public void updateService(String serviceName, String clusters) throws NacosException {
    ServiceInfo oldService = getServiceInfo0(serviceName, clusters);
    try {
        String result = serverProxy.queryList(serviceName, clusters, pushReceiver.getUdpPort(), false);
        if (StringUtils.isNotEmpty(result)) {
            // 将服务端拉取到的服务信息缓存在本地
            processServiceJson(result);
        }
    } finally {
        if (oldService != null) {
            synchronized (oldService) {
                oldService.notifyAll();
            }
        }
    }
}
//查询列表
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));
    //最终调用Http请求拉取服务器服务信息列表
    return reqApi(UtilAndComs.nacosUrlBase + "/instance/list", params, HttpMethod.GET);
} 

3.服务端服务发现

naming项目下的 InstanceController类

@GetMapping("/list")
@Secured(parser = NamingResourceParser.class, action = ActionTypes.READ)
public ObjectNode list(HttpServletRequest request) throws Exception {
    //获取参数并校验
    String namespaceId = WebUtils.optional(request, CommonParams.NAMESPACE_ID, Constants.DEFAULT_NAMESPACE_ID);
    String serviceName = WebUtils.required(request, CommonParams.SERVICE_NAME);
    NamingUtils.checkServiceNameFormat(serviceName);
    String agent = WebUtils.getUserAgent(request);
    String clusters = WebUtils.optional(request, "clusters", StringUtils.EMPTY);
    String clientIP = WebUtils.optional(request, "clientIP", StringUtils.EMPTY);
    int udpPort = Integer.parseInt(WebUtils.optional(request, "udpPort", "0"));
    String env = WebUtils.optional(request, "env", StringUtils.EMPTY);
    boolean isCheck = Boolean.parseBoolean(WebUtils.optional(request, "isCheck", "false"));
    String app = WebUtils.optional(request, "app", StringUtils.EMPTY);
    String tenant = WebUtils.optional(request, "tid", StringUtils.EMPTY);
    boolean healthyOnly = Boolean.parseBoolean(WebUtils.optional(request, "healthyOnly", "false"));
    // 根据命名空间id,服务名获取实例信息
    return doSrvIpxt(namespaceId, serviceName, agent, clusters, clientIP, udpPort, env, isCheck, app, tenant,
            healthyOnly);
}

public ObjectNode doSrvIpxt(String namespaceId, String serviceName, String agent, String clusters, String clientIP,
        int udpPort, String env, boolean isCheck, String app, String tid, boolean healthyOnly) throws Exception {
    ClientInfo clientInfo = new ClientInfo(agent);
    ObjectNode result = JacksonUtils.createEmptyJsonNode();
    //获取服务
    Service service = serviceManager.getService(namespaceId, serviceName);
    long cacheMillis = switchDomain.getDefaultCacheMillis();
    // 尝试启用推送
    try {
        if (udpPort > 0 && pushService.canEnablePush(agent)) {
            pushService.addClient(namespaceId, serviceName, clusters, agent, new InetSocketAddress(clientIP, udpPort),
                            pushDataSource, tid, app);
            cacheMillis = switchDomain.getPushCacheMillis(serviceName);
        }
    } catch (Exception e) {
        Loggers.SRV_LOG.error("[NACOS-API] failed to added push client {}, {}:{}", clientInfo, clientIP, udpPort, e);
        cacheMillis = switchDomain.getDefaultCacheMillis();
    }
    if (service == null) {
        if (Loggers.SRV_LOG.isDebugEnabled()) {
            Loggers.SRV_LOG.debug("no instance to serve for service: {}", serviceName);
        }
        result.put("name", serviceName);
        result.put("clusters", clusters);
        result.put("cacheMillis", cacheMillis);
        result.replace("hosts", JacksonUtils.createEmptyArrayNode());
        return result;
    }
    //检查服务是否禁用
    checkIfDisabled(service);
    List<Instance> srvedIPs;
    // 获取所有永久和临时服务实例
    srvedIPs = service.srvIPs(Arrays.asList(StringUtils.split(clusters, ",")));
    // 选择器过滤服务
    if (service.getSelector() != null && StringUtils.isNotBlank(clientIP)) {
        srvedIPs = service.getSelector().select(clientIP, srvedIPs);
    }
    ...如果找不到服务则返回当前服务
}
//获取所有的永久实例和临时实例
public List<Instance> srvIPs(List<String> clusters) {
    if (CollectionUtils.isEmpty(clusters)) {
        clusters = new ArrayList<>();
        clusters.addAll(clusterMap.keySet());
    }
    return allIPs(clusters);
}
public List<Instance> allIPs() {
    List<Instance> allInstances = new ArrayList<>();
    allInstances.addAll(persistentInstances);
    allInstances.addAll(ephemeralInstances);
    return allInstances;
}

推送服务实例信息

public void addClient(String namespaceId, String serviceName, String clusters, String agent,
        InetSocketAddress socketAddr, DataSource dataSource, String tenant, String app) {
    // 初始化推送客户端
    PushClient client = new PushClient(namespaceId, serviceName, clusters, agent, socketAddr, dataSource, tenant, app);
    addClient(client);
}

// 添加推送目标客户端。
public void addClient(PushClient client) {
    // 客户端由键“ serviceName”存储，因为通知事件由serviceName更改驱动
    String serviceKey = UtilsAndCommons.assembleFullServiceName(client.getNamespaceId(), client.getServiceName());
    ConcurrentMap<String, PushClient> clients = clientMap.get(serviceKey);
    // 如果获取不到推送客户端则新建推送客户端，并缓存
    if (clients == null) {
        clientMap.putIfAbsent(serviceKey, new ConcurrentHashMap<>(1024));
        clients = clientMap.get(serviceKey);
    }
    // 刷新或者缓存
    PushClient oldClient = clients.get(client.toString());
    if (oldClient != null) {
        oldClient.refresh();
    } else {
        PushClient res = clients.putIfAbsent(client.toString(), client);
        if (res != null) {
            Loggers.PUSH.warn("client: {} already associated with key {}", res.getAddrStr(), res.toString());
        }
        Loggers.PUSH.debug("client: {} added for serviceName: {}", client.getAddrStr(), client.getServiceName());
    }
}

总结：

返回指定命名空间下内存注册表中所有的永久实例和临时实例给客户端