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微服务面试篇
文章目录
微服务框架微服务面试篇54 微服务篇54.6 Nacos与Eureka的区别有哪些？【服务发现】54.6.1 Nacos 的服务拉取和订阅 机制
54 微服务篇
54.6 Nacos与Eureka的区别有哪些？【服务发现】
54.6.1 Nacos 的服务拉取和订阅 机制
服务发现：Nacos支持定时拉取和订阅推送两种模式；Eureka只支持定时拉取模式
【Nacos 的服务拉取 和订阅机制】
先看看Nacos 官方API 文档【查询实例 列表】
【描述】
查询服务下的实例列表
【请求类型】
GET
【请求路径】
/nacos/v1/ns/instance/list
【请求参数】
名称类型是否必选描述serviceName字符串是服务名groupName字符串否分组名namespaceId字符串否命名空间IDclusters字符串，多个集群用逗号分隔否集群名称healthyOnlyboolean否，默认为false是否只返回健康实例
现在 Nacos的 服务端肯定需要有一个 controller 来接收这个请求并 返回实例列表
作为消费者【客户端】就应该向 这个服务端 发送这个请求来获取 实例
【问题】
我们的微服务( 比如order-service )，它是什么时候来做这个拉取的 呢？
因为我们的微服务 都是基于Ribbon 来做的远程 调用和负载均衡，所以，服务拉取的动作也是Ribbon 去做的
进到一个 DynamicServerListLoadBalancer类， 动态 列表服务均衡器
它在它的构造函数 中就会执行 一系列的初始化动作
public DynamicServerListLoadBalancer(IClientConfig clientConfig, IRule rule, IPing ping, ServerList
super(clientConfig, rule, ping);
this.isSecure = false;
this.useTunnel = false;
this.serverListUpdateInProgress = new AtomicBoolean(false);
this.updateAction = new NamelessClass_1();
this.serverListImpl = serverList;
this.filter = filter;
this.serverListUpdater = serverListUpdater;
if (filter instanceof AbstractServerListFilter) {
((AbstractServerListFilter)filter).setLoadBalancerStats(this.getLoadBalancerStats());
}
this.restOfInit(clientConfig); // 注意这个【基于rest 请求的初始化】【即基于rest 请求拉取服务列表】
}
跟进这个方法
再跟入 updateListOfServers 这个方法
@VisibleForTesting
public void updateListOfServers() {
List
if (this.serverListImpl != null) {
servers = this.serverListImpl.getUpdatedListOfServers(); //[核心]
LOGGER.debug("List of Servers for {} obtained from Discovery client: {}", this.getIdentifier(), servers);
if (this.filter != null) {
servers = this.filter.getFilteredListOfServers((List)servers);
LOGGER.debug("Filtered List of Servers for {} obtained from Discovery client: {}", this.getIdentifier(), servers);
}
}
this.updateAllServerList((List)servers);
}
跟入 getUpdatedListOfServers 方法
@Override
public List
return getServers();
}
getServers 方法就在下面
【是真的复杂，笔者看到这儿，完全不知道怎么做笔记了 …】
直接回到 服务端 的list 接口 了
*/
@GetMapping("/list")
@Secured(parser = NamingResourceParser.class, action = ActionTypes.READ)
public ObjectNode list(HttpServletRequest request) throws Exception {
// 解析request 中的namespaceId、serviceName
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);
// 获取集群信息
String clusters = WebUtils.optional(request, "clusters", StringUtils.EMPTY);
// 客户端【消费者】的IP 和udp 端口
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"));
return doSrvIpxt(namespaceId, serviceName, agent, clusters, clientIP, udpPort, env, isCheck, app, tenant,
healthyOnly);
}
再进到 doSrvIpxt 方法
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);
// 创建空的json 对象，作为result【将来的 】
ObjectNode result = JacksonUtils.createEmptyJsonNode();
// 从注册表 尝试获取服务
Service service = serviceManager.getService(namespaceId, serviceName);
long cacheMillis = switchDomain.getDefaultCacheMillis();
// now try to enable the push
try {
if (udpPort > 0 && pushService.canEnablePush(agent)) {
// UDP服务端，记录客户端的IP、端口、要监听的服务信息
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();
}
// 【封装最终结果】
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;
}
checkIfDisabled(service);
List
srvedIPs = service.srvIPs(Arrays.asList(StringUtils.split(clusters, ",")));
// filter ips using selector:
if (service.getSelector() != null && StringUtils.isNotBlank(clientIP)) {
srvedIPs = service.getSelector().select(clientIP, srvedIPs);
}
if (CollectionUtils.isEmpty(srvedIPs)) {
if (Loggers.SRV_LOG.isDebugEnabled()) {
Loggers.SRV_LOG.debug("no instance to serve for service: {}", serviceName);
}
if (clientInfo.type == ClientInfo.ClientType.JAVA
&& clientInfo.version.compareTo(VersionUtil.parseVersion("1.0.0")) >= 0) {
result.put("dom", serviceName);
} else {
result.put("dom", NamingUtils.getServiceName(serviceName));
}
result.put("name", serviceName);
result.put("cacheMillis", cacheMillis);
result.put("lastRefTime", System.currentTimeMillis());
result.put("checksum", service.getChecksum());
result.put("useSpecifiedURL", false);
result.put("clusters", clusters);
result.put("env", env);
result.set("hosts", JacksonUtils.createEmptyArrayNode());
result.set("metadata", JacksonUtils.transferToJsonNode(service.getMetadata()));
return result;
}
Map
ipMap.put(Boolean.TRUE, new ArrayList<>());
ipMap.put(Boolean.FALSE, new ArrayList<>());
for (Instance ip : srvedIPs) {
ipMap.get(ip.isHealthy()).add(ip);
}
if (isCheck) {
result.put("reachProtectThreshold", false);
}
double threshold = service.getProtectThreshold();
if ((float) ipMap.get(Boolean.TRUE).size() / srvedIPs.size() <= threshold) {
Loggers.SRV_LOG.warn("protect threshold reached, return all ips, service: {}", serviceName);
if (isCheck) {
result.put("reachProtectThreshold", true);
}
ipMap.get(Boolean.TRUE).addAll(ipMap.get(Boolean.FALSE));
ipMap.get(Boolean.FALSE).clear();
}
if (isCheck) {
result.put("protectThreshold", service.getProtectThreshold());
result.put("reachLocalSiteCallThreshold", false);
return JacksonUtils.createEmptyJsonNode();
}
ArrayNode hosts = JacksonUtils.createEmptyArrayNode();
for (Map.Entry
List
if (healthyOnly && !entry.getKey()) {
continue;
}
for (Instance instance : ips) {
// remove disabled instance:
if (!instance.isEnabled()) {
continue;
}
ObjectNode ipObj = JacksonUtils.createEmptyJsonNode();
ipObj.put("ip", instance.getIp());
ipObj.put("port", instance.getPort());
// deprecated since nacos 1.0.0:
ipObj.put("valid", entry.getKey());
ipObj.put("healthy", entry.getKey());
ipObj.put("marked", instance.isMarked());
ipObj.put("instanceId", instance.getInstanceId());
ipObj.set("metadata", JacksonUtils.transferToJsonNode(instance.getMetadata()));
ipObj.put("enabled", instance.isEnabled());
ipObj.put("weight", instance.getWeight());
ipObj.put("clusterName", instance.getClusterName());
if (clientInfo.type == ClientInfo.ClientType.JAVA
&& clientInfo.version.compareTo(VersionUtil.parseVersion("1.0.0")) >= 0) {
ipObj.put("serviceName", instance.getServiceName());
} else {
ipObj.put("serviceName", NamingUtils.getServiceName(instance.getServiceName()));
}
ipObj.put("ephemeral", instance.isEphemeral());
hosts.add(ipObj);
}
}
result.replace("hosts", hosts);
if (clientInfo.type == ClientInfo.ClientType.JAVA
&& clientInfo.version.compareTo(VersionUtil.parseVersion("1.0.0")) >= 0) {
result.put("dom", serviceName);
} else {
result.put("dom", NamingUtils.getServiceName(serviceName));
}
result.put("name", serviceName);
result.put("cacheMillis", cacheMillis);
result.put("lastRefTime", System.currentTimeMillis());
result.put("checksum", service.getChecksum());
result.put("useSpecifiedURL", false);
result.put("clusters", clusters);
result.put("env", env);
result.replace("metadata", JacksonUtils.transferToJsonNode(service.getMetadata()));
return result;
}
再进到，PushService
里面有一段静态代码块
static {
try {
udpSocket = new DatagramSocket();
Receiver receiver = new Receiver();
Thread inThread = new Thread(receiver);
inThread.setDaemon(true);
inThread.setName("com.alibaba.nacos.naming.push.receiver");
inThread.start();
GlobalExecutor.scheduleRetransmitter(() -> {
try {
// 定时移除已经 断开的客户端
removeClientIfZombie();
} catch (Throwable e) {
Loggers.PUSH.warn("[NACOS-PUSH] failed to remove client zombie");
}
}, 0, 20, TimeUnit.SECONDS);
} catch (SocketException e) {
Loggers.SRV_LOG.error("[NACOS-PUSH] failed to init push service");
}
}
再看到 “监听自己” 的 onApplicationEvent方法
@Override
public void onApplicationEvent(ServiceChangeEvent event) {
// 得到发生变化 的服务
Service service = event.getService();
//得到 服务名称
String serviceName = service.getName();
// 得到 namespaceId
String namespaceId = service.getNamespaceId();
// 用线程池 异步执行任务、发送服务最新数据给 所有的监听者
Future future = GlobalExecutor.scheduleUdpSender(() -> {
try {
Loggers.PUSH.info(serviceName + " is changed, add it to push queue.");
// 得到监听当前服务 【namespaceId, serviceName】 的所有的消费者的 客户端 的PushClient
ConcurrentMap
.get(UtilsAndCommons.assembleFullServiceName(namespaceId, serviceName));
if (MapUtils.isEmpty(clients)) {
return;
}
Map
long lastRefTime = System.nanoTime();
for (PushClient client : clients.values()) {
// 遍历所有的 PushClient
if (client.zombie()) {
// 挂掉 的PushClient，直接移除
Loggers.PUSH.debug("client is zombie: " + client.toString());
clients.remove(client.toString());
Loggers.PUSH.debug("client is zombie: " + client.toString());
continue;
}
// 准备消息
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
if (switchDomain.getDefaultPushCacheMillis() >= 20000 && cache.containsKey(key)) {
org.javatuples.Pair pair = (org.javatuples.Pair) cache.get(key);
compressData = (byte[]) (pair.getValue0());
data = (Map
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));
// 利用UDP 套接字，发送 服务信息
udpPush(ackEntry);
}
} 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);
}
OK，再次回答 我们 的问题
问题说明：考察对Nacos、Eureka的底层实现的掌握情况
难易程度：难
参考话术：
Nacos与Eureka有相同点，也有不同之处，可以从以下几点来描述：
接口方式：Nacos与Eureka都对外暴露了Rest风格的API接口，用来实现服务注册、发现等功能实例类型：Nacos的实例有永久和临时实例之分；而Eureka只支持临时实例健康检测：Nacos对临时实例采用心跳模式检测，对永久实例采用主动请求来检测；Eureka只支持心跳模式服务发现：Nacos支持定时拉取和订阅推送两种模式；Eureka只支持定时拉取模式【这次说了 这个】
Nacos的服务发现分为两种模式：
模式一：主动拉取模式，消费者定期主动从Nacos拉取服务列表并缓存起来，再服务调用时优先读取本地缓存中的服务列表。模式二：订阅模式，消费者订阅Nacos中的服务列表，并基于UDP协议来接收服务变更通知。当Nacos中的服务列表更新时，会发送UDP广播给所有订阅者。
与Eureka相比，Nacos的订阅模式服务状态更新更及时，消费者更容易及时发现服务列表的变化，剔除故障服务。
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