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itemtype=http://schema.org/CreativeWork><meta content="聊聊 Dubbo 的容错机制 | Nicksxs's Blog" itemprop=name><meta content="之前看了 dubbo 的一些代码,在学习过程中,主要关注那些比较“高级”的内容,SPI,自适应扩展等,却忘了一些作为一个 rpc 框架最核心需要的部分,比如如何通信,序列化,网络,容错机制等等,因为其实这个最核心的就是远程调用,自适应扩展其实就是让代码可扩展性,可读性,更优雅等…" itemprop=description></span><header class=post-header><h1 itemprop="name headline" class=post-title>聊聊 Dubbo 的容错机制</h1><div class=post-meta-container><div class=post-meta><span class=post-meta-item><span class=post-meta-item-icon><i class="far fa-calendar"></i> </span><span class=post-meta-item-text>发表于</span> <time itemprop="dateCreated datePublished" title="创建时间:2020-11-22 21:37:55" datetime=2020-11-22T21:37:55+08:00>2020-11-22</time> </span><span class=post-meta-item><span class=post-meta-item-icon><i class="far fa-folder"></i> </span><span class=post-meta-item-text>分类于</span> <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/Java/ itemprop=url rel=index><span itemprop=name>Java</span></a> </span>, <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/Dubbo-RPC/ itemprop=url rel=index><span itemprop=name>Dubbo - RPC</span></a> </span>, <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/Dubbo/ itemprop=url rel=index><span itemprop=name>Dubbo</span></a> </span>, <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/Dubbo/%E5%AE%B9%E9%94%99%E6%9C%BA%E5%88%B6/ itemprop=url rel=index><span itemprop=name>容错机制</span></a> </span></span><span class="post-meta-item cloudflare-page-counter" data-title="聊聊 Dubbo 的容错机制" data-increment=true data-path=/2020/11/22/%E8%81%8A%E8%81%8A-Dubbo-%E7%9A%84%E5%AE%B9%E9%94%99%E6%9C%BA%E5%88%B6/ title=阅读次数><span class=post-meta-item-icon><i class="far fa-eye"></i> </span><span class=post-meta-item-text>阅读次数:</span> <span class=cloudflare-page-counter-count></span></span></div><div class=post-description>之前看了 dubbo 的一些代码,在学习过程中,主要关注那些比较“高级”的内容,SPI,自适应扩展等,却忘了一些作为一个 rpc 框架最核心需要的部分,比如如何通信,序列化,网络,容错机制等等,因为其实这个最核心的就是远程调用,自适应扩展其实就是让代码可扩展性,可读性,更优雅等…</div></div></header><div class=post-body itemprop=articleBody><p>之前看了 dubbo 的一些代码,在学习过程中,主要关注那些比较“高级”的内容,SPI,自适应扩展等,却忘了一些作为一个 rpc 框架最核心需要的部分,比如如何通信,序列化,网络,容错机制等等,因为其实这个最核心的就是远程调用,自适应扩展其实就是让代码可扩展性,可读性,更优雅等,写的搓一点其实也问题不大,但是一个合适的通信协议,序列化方法,如何容错等却是真正保证是一个 rpc 框架最重要的要素。<br>首先来看这张图<br><img alt=cluster data-src=https://img.nicksxs.me/uPic/cluster.jpg><br>在集群调用失败时,Dubbo 提供了多种容错方案,缺省为 failover 重试。<br>各节点关系:<ul><li>这里的 <code>Invoker</code> 是 <code>Provider</code> 的一个可调用 <code>Service</code> 的抽象,<code>Invoker</code> 封装了 <code>Provider</code> 地址及 <code>Service</code> 接口信息<li><code>Directory</code> 代表多个 <code>Invoker</code>,可以把它看成 <code>List<Invoker></code> ,但与 <code>List</code> 不同的是,它的值可能是动态变化的,比如注册中心推送变更<li><code>Cluster</code> 将 <code>Directory</code> 中的多个 <code>Invoker</code> 伪装成一个 <code>Invoker</code>,对上层透明,伪装过程包含了容错逻辑,调用失败后,重试另一个<li><code>Router</code> 负责从多个 <code>Invoker</code> 中按路由规则选出子集,比如读写分离,应用隔离等<li><code>LoadBalance</code> 负责从多个 <code>Invoker</code> 中选出具体的一个用于本次调用,选的过程包含了负载均衡算法,调用失败后,需要重选</ul><h2 id=集群容错模式><a class=headerlink href=#集群容错模式 title=集群容错模式></a>集群容错模式</h2><h3 id=Failover-Cluster><a title="Failover Cluster" class=headerlink href=#Failover-Cluster></a>Failover Cluster</h3><p>失败自动切换,当出现失败,重试其它服务器 1。通常用于读操作,但重试会带来更长延迟。可通过 retries=”2” 来设置重试次数(不含第一次)。<p>重试次数配置如下:<p><dubbo:service retries=”2” /><br>这里重点看下 <code>Failover Cluster</code>集群模式的实现<figure class="highlight java"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br><span class=line>7</span><br><span class=line>8</span><br><span class=line>9</span><br></pre><td class=code><pre><span class=line><span class=keyword>public</span> <span class=keyword>class</span> <span class="title class_">FailoverCluster</span> <span class=keyword>implements</span> <span class="title class_">Cluster</span> {</span><br><span class=line></span><br><span class=line> <span class=keyword>public</span> <span class=keyword>final</span> <span class=keyword>static</span> <span class=type>String</span> <span class=variable>NAME</span> <span class=operator>=</span> <span class=string>"failover"</span>;</span><br><span class=line></span><br><span class=line> <span class=keyword>public</span> <T> Invoker<T> <span class="title function_">join</span><span class=params>(Directory<T> directory)</span> <span class=keyword>throws</span> RpcException {</span><br><span class=line> <span class=keyword>return</span> <span class=keyword>new</span> <span class="title class_">FailoverClusterInvoker</span><T>(directory);</span><br><span class=line> }</span><br><span class=line></span><br><span class=line>}</span><br></pre></table></figure><p>这个代码就非常简单,重点需要看<code>FailoverClusterInvoker</code>里的代码,<code>FailoverClusterInvoker</code>继承了<code>AbstractClusterInvoker</code>类,其中invoke 方法是在抽象类里实现的<figure class="highlight java"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br><span class=line>7</span><br><span class=line>8</span><br><span class=line>9</span><br><span class=line>10</span><br><span class=line>11</span><br><span class=line>12</span><br><span class=line>13</span><br><span class=line>14</span><br><span class=line>15</span><br><span class=line>16</span><br><span class=line>17</span><br><span class=line>18</span><br><span class=line>19</span><br><span class=line>20</span><br></pre><td class=code><pre><span class=line><span class=meta>@Override</span></span><br><span class=line><span class=keyword>public</span> Result <span class="title function_">invoke</span><span class=params>(<span class=keyword>final</span> Invocation invocation)</span> <span class=keyword>throws</span> RpcException {</span><br><span class=line> checkWhetherDestroyed();</span><br><span class=line> <span class=comment>// binding attachments into invocation.</span></span><br><span class=line> <span class=comment>// 绑定 attachments 到 invocation 中.</span></span><br><span class=line> Map<String, Object> contextAttachments = RpcContext.getContext().getObjectAttachments();</span><br><span class=line> <span class=keyword>if</span> (contextAttachments != <span class=literal>null</span> && contextAttachments.size() != <span class=number>0</span>) {</span><br><span class=line> ((RpcInvocation) invocation).addObjectAttachments(contextAttachments);</span><br><span class=line> }</span><br><span class=line> <span class=comment>// 列举 Invoker</span></span><br><span class=line> List<Invoker<T>> invokers = list(invocation);</span><br><span class=line> <span class=comment>// 加载 LoadBalance 负载均衡器</span></span><br><span class=line> <span class=type>LoadBalance</span> <span class=variable>loadbalance</span> <span class=operator>=</span> initLoadBalance(invokers, invocation);</span><br><span class=line> RpcUtils.attachInvocationIdIfAsync(getUrl(), invocation);</span><br><span class=line> <span class=comment>// 调用 实际的 doInvoke 进行后续操作</span></span><br><span class=line> <span class=keyword>return</span> doInvoke(invocation, invokers, loadbalance);</span><br><span class=line>}</span><br><span class=line><span class=comment>// 这是个抽象方法,实际是由子类实现的</span></span><br><span class=line> <span class=keyword>protected</span> <span class=keyword>abstract</span> Result <span class="title function_">doInvoke</span><span class=params>(Invocation invocation, List<Invoker<T>> invokers,</span></span><br><span class=line><span class=params> LoadBalance loadbalance)</span> <span class=keyword>throws</span> RpcException;</span><br></pre></table></figure><p>然后重点就是<code>FailoverClusterInvoker</code>中的<code>doInvoke</code>方法了,其实它里面也就这么一个方法<figure class="highlight java"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br><span class=line>7</span><br><span class=line>8</span><br><span class=line>9</span><br><span class=line>10</span><br><span class=line>11</span><br><span class=line>12</span><br><span class=line>13</span><br><span class=line>14</span><br><span class=line>15</span><br><span class=line>16</span><br><span class=line>17</span><br><span class=line>18</span><br><span class=line>19</span><br><span class=line>20</span><br><span class=line>21</span><br><span class=line>22</span><br><span class=line>23</span><br><span class=line>24</span><br><span class=line>25</span><br><span class=line>26</span><br><span class=line>27</span><br><span class=line>28</span><br><span class=line>29</span><br><span class=line>30</span><br><span class=line>31</span><br><span class=line>32</span><br><span class=line>33</span><br><span class=line>34</span><br><span class=line>35</span><br><span class=line>36</span><br><span class=line>37</span><br><span class=line>38</span><br><span class=line>39</span><br><span class=line>40</span><br><span class=line>41</span><br><span class=line>42</span><br><span class=line>43</span><br><span class=line>44</span><br><span class=line>45</span><br><span class=line>46</span><br><span class=line>47</span><br><span class=line>48</span><br><span class=line>49</span><br><span class=line>50</span><br><span class=line>51</span><br><span class=line>52</span><br><span class=line>53</span><br><span class=line>54</span><br><span class=line>55</span><br><span class=line>56</span><br><span class=line>57</span><br><span class=line>58</span><br><span class=line>59</span><br><span class=line>60</span><br><span class=line>61</span><br><span class=line>62</span><br><span class=line>63</span><br><span class=line>64</span><br><span class=line>65</span><br><span class=line>66</span><br><span class=line>67</span><br><span class=line>68</span><br><span class=line>69</span><br></pre><td class=code><pre><span class=line><span class=meta>@Override</span></span><br><span class=line> <span class=meta>@SuppressWarnings({"unchecked", "rawtypes"})</span></span><br><span class=line> <span class=keyword>public</span> Result <span class="title function_">doInvoke</span><span class=params>(Invocation invocation, <span class=keyword>final</span> List<Invoker<T>> invokers, LoadBalance loadbalance)</span> <span class=keyword>throws</span> RpcException {</span><br><span class=line> List<Invoker<T>> copyInvokers = invokers;</span><br><span class=line> checkInvokers(copyInvokers, invocation);</span><br><span class=line> <span class=type>String</span> <span class=variable>methodName</span> <span class=operator>=</span> RpcUtils.getMethodName(invocation);</span><br><span class=line> <span class=comment>// 获取重试次数,这里默认是 2 次,还有可以注意下后面的+1</span></span><br><span class=line> <span class=type>int</span> <span class=variable>len</span> <span class=operator>=</span> getUrl().getMethodParameter(methodName, RETRIES_KEY, DEFAULT_RETRIES) + <span class=number>1</span>;</span><br><span class=line> <span class=keyword>if</span> (len <= <span class=number>0</span>) {</span><br><span class=line> len = <span class=number>1</span>;</span><br><span class=line> }</span><br><span class=line> <span class=comment>// retry loop.</span></span><br><span class=line> <span class=type>RpcException</span> <span class=variable>le</span> <span class=operator>=</span> <span class=literal>null</span>; <span class=comment>// last exception.</span></span><br><span class=line> List<Invoker<T>> invoked = <span class=keyword>new</span> <span class="title class_">ArrayList</span><Invoker<T>>(copyInvokers.size()); <span class=comment>// invoked invokers.</span></span><br><span class=line> Set<String> providers = <span class=keyword>new</span> <span class="title class_">HashSet</span><String>(len);</span><br><span class=line> <span class=comment>// 循环调用,失败重试</span></span><br><span class=line> <span class=keyword>for</span> (<span class=type>int</span> <span class=variable>i</span> <span class=operator>=</span> <span class=number>0</span>; i < len; i++) {</span><br><span class=line> <span class=comment>//Reselect before retry to avoid a change of candidate `invokers`.</span></span><br><span class=line> <span class=comment>//<span class=doctag>NOTE:</span> if `invokers` changed, then `invoked` also lose accuracy.</span></span><br><span class=line> <span class=keyword>if</span> (i > <span class=number>0</span>) {</span><br><span class=line> checkWhetherDestroyed();</span><br><span class=line> <span class=comment>// 在进行重试前重新列举 Invoker,这样做的好处是,如果某个服务挂了,</span></span><br><span class=line> <span class=comment>// 通过调用 list 可得到最新可用的 Invoker 列表</span></span><br><span class=line> copyInvokers = list(invocation);</span><br><span class=line> <span class=comment>// check again</span></span><br><span class=line> <span class=comment>// 对 copyinvokers 进行判空检查</span></span><br><span class=line> checkInvokers(copyInvokers, invocation);</span><br><span class=line> }</span><br><span class=line> <span class=comment>// 通过负载均衡来选择 invoker</span></span><br><span class=line> Invoker<T> invoker = select(loadbalance, invocation, copyInvokers, invoked);</span><br><span class=line> <span class=comment>// 将其添加到 invoker 到 invoked 列表中</span></span><br><span class=line> invoked.add(invoker);</span><br><span class=line> <span class=comment>// 设置上下文</span></span><br><span class=line> RpcContext.getContext().setInvokers((List) invoked);</span><br><span class=line> <span class=keyword>try</span> {</span><br><span class=line> <span class=comment>// 正式调用</span></span><br><span class=line> <span class=type>Result</span> <span class=variable>result</span> <span class=operator>=</span> invoker.invoke(invocation);</span><br><span class=line> <span class=keyword>if</span> (le != <span class=literal>null</span> && logger.isWarnEnabled()) {</span><br><span class=line> logger.warn(<span class=string>"Although retry the method "</span> + methodName</span><br><span class=line> + <span class=string>" in the service "</span> + getInterface().getName()</span><br><span class=line> + <span class=string>" was successful by the provider "</span> + invoker.getUrl().getAddress()</span><br><span class=line> + <span class=string>", but there have been failed providers "</span> + providers</span><br><span class=line> + <span class=string>" ("</span> + providers.size() + <span class=string>"/"</span> + copyInvokers.size()</span><br><span class=line> + <span class=string>") from the registry "</span> + directory.getUrl().getAddress()</span><br><span class=line> + <span class=string>" on the consumer "</span> + NetUtils.getLocalHost()</span><br><span class=line> + <span class=string>" using the dubbo version "</span> + Version.getVersion() + <span class=string>". Last error is: "</span></span><br><span class=line> + le.getMessage(), le);</span><br><span class=line> }</span><br><span class=line> <span class=keyword>return</span> result;</span><br><span class=line> } <span class=keyword>catch</span> (RpcException e) {</span><br><span class=line> <span class=keyword>if</span> (e.isBiz()) { <span class=comment>// biz exception.</span></span><br><span class=line> <span class=keyword>throw</span> e;</span><br><span class=line> }</span><br><span class=line> le = e;</span><br><span class=line> } <span class=keyword>catch</span> (Throwable e) {</span><br><span class=line> le = <span class=keyword>new</span> <span class="title class_">RpcException</span>(e.getMessage(), e);</span><br><span class=line> } <span class=keyword>finally</span> {</span><br><span class=line> providers.add(invoker.getUrl().getAddress());</span><br><span class=line> }</span><br><span class=line> }</span><br><span class=line> <span class=keyword>throw</span> <span class=keyword>new</span> <span class="title class_">RpcException</span>(le.getCode(), <span class=string>"Failed to invoke the method "</span></span><br><span class=line> + methodName + <span class=string>" in the service "</span> + getInterface().getName()</span><br><span class=line> + <span class=string>". Tried "</span> + len + <span class=string>" times of the providers "</span> + providers</span><br><span class=line> + <span class=string>" ("</span> + providers.size() + <span class=string>"/"</span> + copyInvokers.size()</span><br><span class=line> + <span class=string>") from the registry "</span> + directory.getUrl().getAddress()</span><br><span class=line> + <span class=string>" on the consumer "</span> + NetUtils.getLocalHost() + <span class=string>" using the dubbo version "</span></span><br><span class=line> + Version.getVersion() + <span class=string>". Last error is: "</span></span><br><span class=line> + le.getMessage(), le.getCause() != <span class=literal>null</span> ? le.getCause() : le);</span><br><span class=line> }</span><br></pre></table></figure><h3 id=Failfast-Cluster><a title="Failfast Cluster" class=headerlink href=#Failfast-Cluster></a>Failfast Cluster</h3><p>快速失败,只发起一次调用,失败立即报错。通常用于非幂等性的写操作,比如新增记录。<h3 id=Failsafe-Cluster><a title="Failsafe Cluster" class=headerlink href=#Failsafe-Cluster></a>Failsafe Cluster</h3><p>失败安全,出现异常时,直接忽略。通常用于写入审计日志等操作。<h3 id=Failback-Cluster><a title="Failback Cluster" class=headerlink href=#Failback-Cluster></a>Failback Cluster</h3><p>失败自动恢复,后台记录失败请求,定时重发。通常用于消息通知操作。<h3 id=Forking-Cluster><a title="Forking Cluster" class=headerlink href=#Forking-Cluster></a>Forking Cluster</h3><p>并行调用多个服务器,只要一个成功即返回。通常用于实时性要求较高的读操作,但需要浪费更多服务资源。可通过 forks=”2” 来设置最大并行数。<h3 id=Broadcast-Cluster><a title="Broadcast Cluster" class=headerlink href=#Broadcast-Cluster></a>Broadcast Cluster</h3><p>广播调用所有提供者,逐个调用,任意一台报错则报错 2。通常用于通知所有提供者更新缓存或日志等本地资源信息。</div><footer class=post-footer><div class="affiliate-creative affiliate-creative--post-end" data-affiliate-id=tencent-cloud-general><a rel="sponsored noopener" aria-label=腾讯云产品优惠 href=https://cloud.tencent.com/act/cps/redirect?redirect=2446&cps_key=2e33a1eedb380997d03618b4a5ba6ca7&from=console target=_blank><img alt=腾讯云服务器、数据库和云产品优惠 decoding=async height=419 loading=lazy src=/uploads/affiliate/tencent-cloud-general.webp width=690> </a><span class=affiliate-disclosure>推广</span></div><div class=reward-container><div>请我一杯咖啡吧!</div><button>赞赏</button><div class=post-reward><div><img alt="Nicksxs 微信" src=https://i.loli.net/2020/01/12/NUlWanT31E8LQGx.png><span>微信</span></div><div><img alt="Nicksxs 支付宝" src=https://ooo.0o0.ooo/2016/08/17/57b421e773057.jpg><span>支付宝</span></div></div></div><div class=post-copyright><ul><li class=post-copyright-author><strong>本文作者: </strong>Nicksxs<li 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