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Dubbo分析之Registry层

日期:2018-12-21点击:313

系列文章

Dubbo分析Serialize层
Dubbo分析之Transport层
Dubbo分析之Exchange 层
Dubbo分析之Protocol层
Dubbo分析之Cluster层
Dubbo分析之Registry层

前言

紧接上文Dubbo分析之Cluster层,本文继续分析dubbo的register层;此层封装服务地址的注册与发现,以服务URL为中心,扩展接口为RegistryFactory, Registry, RegistryService;

Registry接口

接口定义如下:

public interface Registry extends Node, RegistryService { } public interface RegistryService { void register(URL url); void unregister(URL url); void subscribe(URL url, NotifyListener listener); void unsubscribe(URL url, NotifyListener listener); List<URL> lookup(URL url); }

主要提供了注册(register),注销(unregister),订阅(subscribe),退订(unsubscribe)等功能;dubbo提供了多种注册方式分别是:Multicast ,Zookeeper,Redis以及Simple方式;
Multicast:Multicast注册中心不需要启动任何中心节点,只要广播地址一样,就可以互相发现;
Zookeeper:Zookeeper是Apacahe Hadoop的子项目,是一个树型的目录服务,支持变更推送,适合作为Dubbo服务的注册中心,工业强度较高,可用于生产环境,并推荐使用;
Redis:基于Redis实现的注册中心,使用 Redis的Publish/Subscribe事件通知数据变更;
Simple:Simple注册中心本身就是一个普通的Dubbo服务,可以减少第三方依赖,使整体通讯方式一致;
后面重点介绍官方推荐的Zookeeper注册方式;具体的Register是在RegistryFactory中生成的,具体看一下接口定义;

RegistryFactory接口

接口定义如下:

@SPI("dubbo") public interface RegistryFactory { @Adaptive({"protocol"}) Registry getRegistry(URL url); }

RegistryFactory提供了SPI扩展,默认使用dubbo,具体有哪些扩展可以查看META-INF/dubbo/internal/com.alibaba.dubbo.registry.RegistryFactory:

dubbo=com.alibaba.dubbo.registry.dubbo.DubboRegistryFactory multicast=com.alibaba.dubbo.registry.multicast.MulticastRegistryFactory zookeeper=com.alibaba.dubbo.registry.zookeeper.ZookeeperRegistryFactory redis=com.alibaba.dubbo.registry.redis.RedisRegistryFactory

已推荐使用的Zookeeper为实例,查看ZookeeperRegistryFactory,提供了createRegistry方法:

private ZookeeperTransporter zookeeperTransporter; public Registry createRegistry(URL url) { return new ZookeeperRegistry(url, zookeeperTransporter); }

实例化ZookeeperRegistry,两个参数分别是url和zookeeperTransporter,zookeeperTransporter是操作Zookeeper的客户端组件包括:zkclient和curator两种方式

@SPI("curator") public interface ZookeeperTransporter { @Adaptive({Constants.CLIENT_KEY, Constants.TRANSPORTER_KEY}) ZookeeperClient connect(URL url); }

ZookeeperTransporter同样提供了SPI扩展,默认使用curator方式;接下来重点看一下Zookeeper注册中心。

Zookeeper注册中心

1.整体设计流程

在dubbo的整体设计中,可以大致查看Registry层的大致流程,首先通过RegistryFactory实例化Registry,Registry可以接收RegistryProtocol传过来的注册(register)和订阅(subscribe)消息,然后Registry通过ZKClient来向Zookeeper指定的目录下写入url信息,如果是订阅消息Registry会通过NotifyListener来通知RegitryDirctory进行更新url,最后就是Cluster层通过路由,负载均衡选择具体的提供方;

2.Zookeeper注册中心流程

官方提供了dubbo在Zookeeper中心的流程图:

流程说明:
服务提供者启动时: 向/dubbo/com.foo.BarService/providers目录下写入自己的URL地址;
服务消费者启动时: 订阅/dubbo/com.foo.BarService/providers目录下的提供者URL地址;并向/dubbo/com.foo.BarService/consumers目录下写入自己的URL地址;
监控中心启动时: 订阅/dubbo/com.foo.BarService 目录下的所有提供者和消费者URL地址。
下面分别从注册(register),注销(unregister),订阅(subscribe),退订(unsubscribe)四个方面来分析

3.注册(register)

ZookeeperRegistry的父类FailbackRegistry中实现了register方法,FailbackRegistry从名字可以看出来具有:失败自动恢复,后台记录失败请求,定时重发功能;下面具体看一下register方法:

public void register(URL url) { super.register(url); failedRegistered.remove(url); failedUnregistered.remove(url); try { // Sending a registration request to the server side doRegister(url); } catch (Exception e) { Throwable t = e; // If the startup detection is opened, the Exception is thrown directly. boolean check = getUrl().getParameter(Constants.CHECK_KEY, true) && url.getParameter(Constants.CHECK_KEY, true) && !Constants.CONSUMER_PROTOCOL.equals(url.getProtocol()); boolean skipFailback = t instanceof SkipFailbackWrapperException; if (check || skipFailback) { if (skipFailback) { t = t.getCause(); } throw new IllegalStateException("Failed to register " + url + " to registry " + getUrl().getAddress() + ", cause: " + t.getMessage(), t); } else { logger.error("Failed to register " + url + ", waiting for retry, cause: " + t.getMessage(), t); } // Record a failed registration request to a failed list, retry regularly failedRegistered.add(url); } }

后台记录了失败的请求,包括failedRegistered和failedUnregistered,注册的时候将里面存放的url删除,然后执行doRegister方法,此方式在ZookeeperRegistry中实现,主要是在Zookeeper指定的目录下写入url信息,如果失败会记录注册失败的url,等待自动恢复;doRegister相关代码如下:

protected void doRegister(URL url) { try { zkClient.create(toUrlPath(url), url.getParameter(Constants.DYNAMIC_KEY, true)); } catch (Throwable e) { throw new RpcException("Failed to register " + url + " to zookeeper " + getUrl() + ", cause: " + e.getMessage(), e); } }

调用zkClient的create方法在Zookeeper上创建节点,默认创建临时节点,create方法在AbstractZookeeperClient中实现,具体源码如下:

public void create(String path, boolean ephemeral) { if (!ephemeral) { if (checkExists(path)) { return; } } int i = path.lastIndexOf('/'); if (i > 0) { create(path.substring(0, i), false); } if (ephemeral) { createEphemeral(path); } else { createPersistent(path); } }

path指定需要创建的目录,ephemeral指定是否是创建临时节点,并且提供了递归创建目录,除了叶子目录其他目录都是持久化的;可以发现不管是创建临时目录还是持久化目录,都没有指定目录的Data,所有使用的是默认值,也就是本地ip地址;实例中创建的目录如下:

/dubbo/com.dubboApi.DemoService/providers/dubbo%3A%2F%2F10.13.83.7%3A20880%2Fcom.dubboApi.DemoService%3Fanyhost%3Dtrue%26application%3Dhello-world-app%26dubbo%3D2.0.2%26generic%3Dfalse%26interface%3Dcom.dubboApi.DemoService%26methods%3DsyncSayHello%2CsayHello%2CasyncSayHello%26pid%3D13252%26serialization%3Dprotobuf%26side%3Dprovider%26timestamp%3D1545297239027

dubbo是一个根节点,然后是service名称,providers是固定的一个类型,如果是消费端这里就是consumers,最后就是一个临时节点;使用临时节点的目的就是提供者出现断电等异常停机时,注册中心能自动删除提供者信息;可以通过如下方法查询当前的目录节点信息:

public class CuratorTest { static String path = "/dubbo"; static CuratorFramework client = CuratorFrameworkFactory.builder().connectString("127.0.0.1:2181") .sessionTimeoutMs(5000).retryPolicy(new ExponentialBackoffRetry(1000, 3)).build(); public static void main(String[] args) throws Exception { client.start(); List<String> paths = listChildren(path); for (String path : paths) { Stat stat = new Stat(); System.err.println( "path:" + path + ",value:" + new String(client.getData().storingStatIn(stat).forPath(path))); } } private static List<String> listChildren(String path) throws Exception { List<String> pathList = new ArrayList<String>(); pathList.add(path); List<String> list = client.getChildren().forPath(path); if (list != null && list.size() > 0) { for (String cPath : list) { String temp = ""; if ("/".equals(path)) { temp = path + cPath; } else { temp = path + "/" + cPath; } pathList.addAll(listChildren(temp)); } } return pathList; } }

递归遍历/dubbo目录下的所有子目录,同时将节点存储的数据都查询出来,结果如下:

path:/dubbo,value:10.13.83.7 path:/dubbo/com.dubboApi.DemoService,value:10.13.83.7 path:/dubbo/com.dubboApi.DemoService/configurators,value:10.13.83.7 path:/dubbo/com.dubboApi.DemoService/providers,value:10.13.83.7 path:/dubbo/com.dubboApi.DemoService/providers/dubbo%3A%2F%2F10.13.83.7%3A20880%2Fcom.dubboApi.DemoService%3Fanyhost%3Dtrue%26application%3Dhello-world-app%26dubbo%3D2.0.2%26generic%3Dfalse%26interface%3Dcom.dubboApi.DemoService%26methods%3DsyncSayHello%2CsayHello%2CasyncSayHello%26pid%3D4712%26serialization%3Dprotobuf%26side%3Dprovider%26timestamp%3D1545358401966,value:10.13.83.7

除了最后一个节点是临时节点,其他都是持久化的;

4.注销(unregister)

同样在父类FailbackRegistry中实现了unregister方法,代码如下:

public void unregister(URL url) { super.unregister(url); failedRegistered.remove(url); failedUnregistered.remove(url); try { // Sending a cancellation request to the server side doUnregister(url); } catch (Exception e) { Throwable t = e; // If the startup detection is opened, the Exception is thrown directly. boolean check = getUrl().getParameter(Constants.CHECK_KEY, true) && url.getParameter(Constants.CHECK_KEY, true) && !Constants.CONSUMER_PROTOCOL.equals(url.getProtocol()); boolean skipFailback = t instanceof SkipFailbackWrapperException; if (check || skipFailback) { if (skipFailback) { t = t.getCause(); } throw new IllegalStateException("Failed to unregister " + url + " to registry " + getUrl().getAddress() + ", cause: " + t.getMessage(), t); } else { logger.error("Failed to uregister " + url + ", waiting for retry, cause: " + t.getMessage(), t); } // Record a failed registration request to a failed list, retry regularly failedUnregistered.add(url); } }

注销时同样删除了failedRegistered和failedUnregistered存放的url,然后调用doUnregister,删除Zookeeper中的目录节点,失败的情况下会存储在failedUnregistered中,等待重试;

protected void doUnregister(URL url) { try { zkClient.delete(toUrlPath(url)); } catch (Throwable e) { throw new RpcException("Failed to unregister " + url + " to zookeeper " + getUrl() + ", cause: " + e.getMessage(), e); } } //CuratorZookeeperClient删除操作 public void delete(String path) { try { client.delete().forPath(path); } catch (NoNodeException e) { } catch (Exception e) { throw new IllegalStateException(e.getMessage(), e); } }

直接使用CuratorZookeeperClient中的delete方法删除临时节点;

5.订阅(subscribe)

服务消费者启动时,会先向Zookeeper注册消费者节点信息,然后订阅…/providers目录下提供者的URL地址;消费端也同样需要注册节点信息,是因为监控中心需要对服务端和消费端都进行监控;下面重点看一下订阅的相关代码,在父类FailbackRegistry中实现了subscribe方法:

public void subscribe(URL url, NotifyListener listener) { super.subscribe(url, listener); removeFailedSubscribed(url, listener); try { // Sending a subscription request to the server side doSubscribe(url, listener); } catch (Exception e) { Throwable t = e; List<URL> urls = getCacheUrls(url); if (urls != null && !urls.isEmpty()) { notify(url, listener, urls); logger.error("Failed to subscribe " + url + ", Using cached list: " + urls + " from cache file: " + getUrl().getParameter(Constants.FILE_KEY, System.getProperty("user.home") + "/dubbo-registry-" + url.getHost() + ".cache") + ", cause: " + t.getMessage(), t); } else { // If the startup detection is opened, the Exception is thrown directly. boolean check = getUrl().getParameter(Constants.CHECK_KEY, true) && url.getParameter(Constants.CHECK_KEY, true); boolean skipFailback = t instanceof SkipFailbackWrapperException; if (check || skipFailback) { if (skipFailback) { t = t.getCause(); } throw new IllegalStateException("Failed to subscribe " + url + ", cause: " + t.getMessage(), t); } else { logger.error("Failed to subscribe " + url + ", waiting for retry, cause: " + t.getMessage(), t); } } // Record a failed registration request to a failed list, retry regularly addFailedSubscribed(url, listener); } }

类似的格式,同样存储了失败了订阅url信息,重点看ZookeeperRegistry中的doSubscribe方法:

private final ConcurrentMap<URL, ConcurrentMap<NotifyListener, ChildListener>> zkListeners = new ConcurrentHashMap<URL, ConcurrentMap<NotifyListener, ChildListener>>(); protected void doSubscribe(final URL url, final NotifyListener listener) { try { if (Constants.ANY_VALUE.equals(url.getServiceInterface())) { String root = toRootPath(); ConcurrentMap<NotifyListener, ChildListener> listeners = zkListeners.get(url); if (listeners == null) { zkListeners.putIfAbsent(url, new ConcurrentHashMap<NotifyListener, ChildListener>()); listeners = zkListeners.get(url); } ChildListener zkListener = listeners.get(listener); if (zkListener == null) { listeners.putIfAbsent(listener, new ChildListener() { @Override public void childChanged(String parentPath, List<String> currentChilds) { for (String child : currentChilds) { child = URL.decode(child); if (!anyServices.contains(child)) { anyServices.add(child); subscribe(url.setPath(child).addParameters(Constants.INTERFACE_KEY, child, Constants.CHECK_KEY, String.valueOf(false)), listener); } } } }); zkListener = listeners.get(listener); } zkClient.create(root, false); List<String> services = zkClient.addChildListener(root, zkListener); if (services != null && !services.isEmpty()) { for (String service : services) { service = URL.decode(service); anyServices.add(service); subscribe(url.setPath(service).addParameters(Constants.INTERFACE_KEY, service, Constants.CHECK_KEY, String.valueOf(false)), listener); } } } else { List<URL> urls = new ArrayList<URL>(); for (String path : toCategoriesPath(url)) { ConcurrentMap<NotifyListener, ChildListener> listeners = zkListeners.get(url); if (listeners == null) { zkListeners.putIfAbsent(url, new ConcurrentHashMap<NotifyListener, ChildListener>()); listeners = zkListeners.get(url); } ChildListener zkListener = listeners.get(listener); if (zkListener == null) { listeners.putIfAbsent(listener, new ChildListener() { @Override public void childChanged(String parentPath, List<String> currentChilds) { ZookeeperRegistry.this.notify(url, listener, toUrlsWithEmpty(url, parentPath, currentChilds)); } }); zkListener = listeners.get(listener); } zkClient.create(path, false); List<String> children = zkClient.addChildListener(path, zkListener); if (children != null) { urls.addAll(toUrlsWithEmpty(url, path, children)); } } notify(url, listener, urls); } } catch (Throwable e) { throw new RpcException("Failed to subscribe " + url + " to zookeeper " + getUrl() + ", cause: " + e.getMessage(), e); } }

在ZookeeperRegistry中定义了一个zkListeners变量,每个URL对应了一个map;map里面分别是NotifyListener和ChildListener的对应关系,消费端订阅时这里的NotifyListener其实就是RegistryDirectory,ChildListener是一个内部类,用来在监听的节点发生变更时,通知对应的消费端,具体的监听处理是在zkClient.addChildListener中实现的:

public List<String> addChildListener(String path, final ChildListener listener) { ConcurrentMap<ChildListener, TargetChildListener> listeners = childListeners.get(path); if (listeners == null) { childListeners.putIfAbsent(path, new ConcurrentHashMap<ChildListener, TargetChildListener>()); listeners = childListeners.get(path); } TargetChildListener targetListener = listeners.get(listener); if (targetListener == null) { listeners.putIfAbsent(listener, createTargetChildListener(path, listener)); targetListener = listeners.get(listener); } return addTargetChildListener(path, targetListener); } public CuratorWatcher createTargetChildListener(String path, ChildListener listener) { return new CuratorWatcherImpl(listener); } public List<String> addTargetChildListener(String path, CuratorWatcher listener) { try { return client.getChildren().usingWatcher(listener).forPath(path); } catch (NoNodeException e) { return null; } catch (Exception e) { throw new IllegalStateException(e.getMessage(), e); } } private class CuratorWatcherImpl implements CuratorWatcher { private volatile ChildListener listener; public CuratorWatcherImpl(ChildListener listener) { this.listener = listener; } public void unwatch() { this.listener = null; } @Override public void process(WatchedEvent event) throws Exception { if (listener != null) { String path = event.getPath() == null ? "" : event.getPath(); listener.childChanged(path, StringUtils.isNotEmpty(path) ? client.getChildren().usingWatcher(this).forPath(path) : Collections.<String>emptyList()); } } }

CuratorWatcherImpl实现了Zookeeper的监听接口CuratorWatcher,用来在节点有变更时通知对应的ChildListener,这样ChildListener就可以通知RegistryDirectory进行更新数据;

6.退订(unsubscribe)

在父类FailbackRegistry中实现了unsubscribe方法

public void unsubscribe(URL url, NotifyListener listener) { super.unsubscribe(url, listener); removeFailedSubscribed(url, listener); try { // Sending a canceling subscription request to the server side doUnsubscribe(url, listener); } catch (Exception e) { Throwable t = e; // If the startup detection is opened, the Exception is thrown directly. boolean check = getUrl().getParameter(Constants.CHECK_KEY, true) && url.getParameter(Constants.CHECK_KEY, true); boolean skipFailback = t instanceof SkipFailbackWrapperException; if (check || skipFailback) { if (skipFailback) { t = t.getCause(); } throw new IllegalStateException("Failed to unsubscribe " + url + " to registry " + getUrl().getAddress() + ", cause: " + t.getMessage(), t); } else { logger.error("Failed to unsubscribe " + url + ", waiting for retry, cause: " + t.getMessage(), t); } // Record a failed registration request to a failed list, retry regularly Set<NotifyListener> listeners = failedUnsubscribed.get(url); if (listeners == null) { failedUnsubscribed.putIfAbsent(url, new ConcurrentHashSet<NotifyListener>()); listeners = failedUnsubscribed.get(url); } listeners.add(listener); } }

同样使用failedUnsubscribed用来存储失败退订的url,具体看ZookeeperRegistry中的doUnsubscribe方法

protected void doUnsubscribe(URL url, NotifyListener listener) { ConcurrentMap<NotifyListener, ChildListener> listeners = zkListeners.get(url); if (listeners != null) { ChildListener zkListener = listeners.get(listener); if (zkListener != null) { if (Constants.ANY_VALUE.equals(url.getServiceInterface())) { String root = toRootPath(); zkClient.removeChildListener(root, zkListener); } else { for (String path : toCategoriesPath(url)) { zkClient.removeChildListener(path, zkListener); } } } } }

退订就比较简单了,只需要移除监听器就可以了;

7.失败重试

FailbackRegistry从名字可以看出来具有:失败自动恢复,后台记录失败请求,定时重发功能;在FailbackRegistry的构造器中启动了一个定时器:

this.retryFuture = retryExecutor.scheduleWithFixedDelay(new Runnable() { @Override public void run() { // Check and connect to the registry try { retry(); } catch (Throwable t) { // Defensive fault tolerance logger.error("Unexpected error occur at failed retry, cause: " + t.getMessage(), t); } } }, retryPeriod, retryPeriod, TimeUnit.MILLISECONDS);

实例化了一个间隔5秒执行一次重试的定时器,retry部分代码如下:

protected void retry() { if (!failedRegistered.isEmpty()) { Set<URL> failed = new HashSet<URL>(failedRegistered); if (failed.size() > 0) { if (logger.isInfoEnabled()) { logger.info("Retry register " + failed); } try { for (URL url : failed) { try { doRegister(url); failedRegistered.remove(url); } catch (Throwable t) { // Ignore all the exceptions and wait for the next retry logger.warn("Failed to retry register " + failed + ", waiting for again, cause: " + t.getMessage(), t); } } } catch (Throwable t) { // Ignore all the exceptions and wait for the next retry logger.warn("Failed to retry register " + failed + ", waiting for again, cause: " + t.getMessage(), t); } } } ...省略... }

定期检查是否存在失败的注册(register),注销(unregister),订阅(subscribe),退订(unsubscribe)URL,如果存在则重试;

总结

本文首先介绍了RegistryFactory, Registry, RegistryService几个核心接口,然后以Zookeeper为注册中心重点介绍了注册(register),注销(unregister),订阅(subscribe),退订(unsubscribe)方式。

示例代码地址

https://github.com/ksfzhaohui...
https://gitee.com/OutOfMemory...

 

原文链接:https://my.oschina.net/OutOfMemory/blog/2991498
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