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<h2 class="post-title" itemprop="name headline">[Kubernetes] DNS Setting with Dockerd(原始碼分析下)
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<div class="post-description">在前篇文章有跟大家分享過實際部屬上遇到的 DNS 問題，並且透過實驗佐證去觀察結果, 本篇文章則是透過另外一種觀點來觀察結果,透過閱讀原始碼的方式來觀察到底 kubernetes 再創建相關的 Pod 時會如何去處理 DNS 相關的設定，由於整個過程牽扯到 kubernetes 以及 CRI(Container Runtime Interface)的操作，而我們預設使用的則是 Docker 作為底層容器的操作. 本篇文章會針對後半部分，也就是所謂的 docker(dockerd) 本身再創建容器的時候，會如何處理其 DNS 相關的設定，透過閱讀 docker-ce 以及 libnetwork 相關的原始碼，不但能夠更清楚的釐清全部的運作原理，也能夠學習到 docker 底層實踐的過程與精神</div>
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<h1 id="Preface"><a href="#Preface" class="headerlink" title="Preface"></a>Preface</h1><p>此篇文章是 Kubernetes Pod-DNS 系列文章最後一篇<br>此系列文會從使用者的用法到一些問題的發掘，最後透過閱讀程式碼的方式去分析這些問題</p>
<p>相關的文章連結如下</p>
<ul>
<li><a href="https://www.hwchiu.com/kubernetes-dns.html">[Kubernetes] DNS setting in your Pod</a></li>
<li><a href="https://www.hwchiu.com/kubernetes-dns-ii.html">[Kubernetes] DNS Setting with Dockerd</a></li>
<li><a href="https://www.hwchiu.com/kubernetes-dns-iii.html">[Kubernetes] DNS Setting with Dockerd(原始碼分析上)</a></li>
</ul>
<h1 id="正文"><a href="#正文" class="headerlink" title="正文"></a>正文</h1><p>再上篇文章 - <a href="https://www.hwchiu.com/kubernetes-dns-iii.html">[Kubernetes] DNS Setting with Dockerd(原始碼分析上)</a> 中，我們透過閱讀 <code>kubernetes</code> 原始碼的方式已經理解到 <code>kubernetes</code> 本身是怎麼去處理 <code>DNS</code> 的設定。 但是卻留下了一個謎團就是 <code>dockerd</code> 到底如何處理每個容器本身的 <code>DNS</code> 設定?</p>
<p>重新複習一次之前觀察到的結果</p>
<table>
<thead>
<tr>
<th>node\dockerd</th>
<th>有設定 DNS</th>
<th>沒設定 DNS</th>
</tr>
</thead>
<tbody>
<tr>
<td>有數值</td>
<td>node</td>
<td>node</td>
</tr>
<tr>
<td>沒有數值</td>
<td>dockerd</td>
<td>8.8.8.8</td>
</tr>
</tbody>
</table>
<p>這邊直接開門見山的說明結論<br>當每次創建容器時，大抵上都會遵循下列邏輯</p>
<ol>
<li>先根據參數<code>resolveConf</code> 來讀取當前 <code>DNS</code> 的全部設定</li>
<li>如果使用者有自行設定 <code>DNS</code> 的參數，就會全面使用這邊的設定，完全忽略(1)載入的設定</li>
<li>如果使用者沒有自行設定 <code>DNS</code> 的話，就會針對 (1) 載入的設定進行一次過濾<ul>
<li>針對 127.0.0.1/8 之類的進行過濾</li>
<li>過濾後若發現是空的，則補上 8.8.8.8/8.8.4.4</li>
</ul>
</li>
</ol>
<p>接下來我們就會透過直接閱讀 <code>docker-ce</code> 原始碼的方式來理解這個問題</p>
<a id="more"></a>
<h1 id="dockerd"><a href="#dockerd" class="headerlink" title="dockerd"></a>dockerd</h1><p>如同前篇文章所說，要透過閱讀原始碼找尋問題的最大困難點就是起點，要先想辦法找到與目標問題有關的進入點，然後從該進入點開始挖掘跟目標有關的程式碼。</p>
<p>這邊使用上次的那張流程圖，將其修改一下來符合本篇的方向來看。</p>
<p>首先，當 <code>kubelet</code> 透過 <code>CRI (Contaienr Runtime Interface)</code> 將容器相關的操作請求送到 <code>docekrd</code> 後就會開始進行容器的創見/刪除/修改</p>
<p>假設我們要進行的創建容器這個操作，以 <code>dockerd</code> 的角度來說用比較簡單的方式來看大概就是</p>
<ol>
<li>創建容器</li>
<li>對該容器設定相關規則<ul>
<li>網路相關功能</li>
<li>AppArmor 相關</li>
<li>…等各式各樣的功能</li>
</ul>
</li>
</ol>
<p><img src="https://i.imgur.com/HBxFvzA.png" alt="Imgur"></p>
<p>上面只是一個比較抽象的方式去描述整個過程，我們想要瞭解的<code>DNS</code>相關的設定都在所謂的 <code>Config Network</code> 裡面。</p>
<p>接下來幫大家節省時間，直接將詳細用到的程式碼流程列在下列圖表中<br><img src="https://i.imgur.com/AElxokT.png" alt="Imgur"></p>
<p>我們接下來就直接從整個創造容器的起點 <code>ContaienrStart</code> 來開始看吧!</p>
<h1 id="程式碼研究"><a href="#程式碼研究" class="headerlink" title="程式碼研究"></a>程式碼研究</h1><h2 id="ContainerStart"><a href="#ContainerStart" class="headerlink" title="ContainerStart"></a>ContainerStart</h2><figure class="highlight go"><figcaption><span>ContaienrStart</span><a href="https://github.com/docker/docker-ce/blob/da1e08d48493406ce290a1b99269e52879af5b0e/components/engine/daemon/start.go#L18" target="_blank" rel="noopener">start.go</a></figcaption><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></pre></td><td class="code"><pre><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">func</span> <span class="params">(daemon *Daemon)</span> <span class="title">ContainerStart</span><span class="params">(name <span class="keyword">string</span>, hostConfig *containertypes.HostConfig, checkpoint <span class="keyword">string</span>, checkpointDir <span class="keyword">string</span>)</span> <span class="title">error</span></span> {</span><br><span class="line">...</span><br><span class="line"> <span class="comment">// check if hostConfig is in line with the current system settings.</span></span><br><span class="line"> <span class="comment">// It may happen cgroups are umounted or the like.</span></span><br><span class="line"> <span class="keyword">if</span> _, err = daemon.verifyContainerSettings(container.OS, container.HostConfig, <span class="literal">nil</span>, <span class="literal">false</span>); err != <span class="literal">nil</span> {</span><br><span class="line"> <span class="keyword">return</span> errdefs.InvalidParameter(err)</span><br><span class="line"> }</span><br><span class="line"> <span class="comment">// Adapt for old containers in case we have updates in this function and</span></span><br><span class="line"> <span class="comment">// old containers never have chance to call the new function in create stage.</span></span><br><span class="line"> <span class="keyword">if</span> hostConfig != <span class="literal">nil</span> {</span><br><span class="line"> <span class="keyword">if</span> err := daemon.adaptContainerSettings(container.HostConfig, <span class="literal">false</span>); err != <span class="literal">nil</span> {</span><br><span class="line"> <span class="keyword">return</span> errdefs.InvalidParameter(err)</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">return</span> daemon.containerStart(container, checkpoint, checkpointDir, <span class="literal">true</span>)</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>這邊的邏輯基本上就是處理一些 <code>Container</code> 相關設定，最後直接呼叫一個私有函式 <code>containerStart</code> 來進行更進一步的處理</p>
<h2 id="containerStart"><a href="#containerStart" class="headerlink" title="containerStart"></a>containerStart</h2><figure class="highlight go"><figcaption><span>containerStart</span><a href="https://github.com/docker/docker-ce/blob/da1e08d48493406ce290a1b99269e52879af5b0e/components/engine/daemon/start.go#L102" target="_blank" rel="noopener">start.go</a></figcaption><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></pre></td><td class="code"><pre><span class="line"></span><br><span class="line"><span class="comment">// containerStart prepares the container to run by setting up everything the</span></span><br><span class="line"><span class="comment">// container needs, such as storage and networking, as well as links</span></span><br><span class="line"><span class="comment">// between containers. The container is left waiting for a signal to</span></span><br><span class="line"><span class="comment">// begin running.</span></span><br><span class="line"><span class="function"><span class="keyword">func</span> <span class="params">(daemon *Daemon)</span> <span class="title">containerStart</span><span class="params">(container *container.Container, checkpoint <span class="keyword">string</span>, checkpointDir <span class="keyword">string</span>, resetRestartManager <span class="keyword">bool</span>)</span> <span class="params">(err error)</span></span> {</span><br><span class="line"></span><br><span class="line">....</span><br><span class="line"> <span class="keyword">if</span> err := daemon.conditionalMountOnStart(container); err != <span class="literal">nil</span> {</span><br><span class="line"> <span class="keyword">return</span> err</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> err := daemon.initializeNetworking(container); err != <span class="literal">nil</span> {</span><br><span class="line"> <span class="keyword">return</span> err</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line">....</span><br><span class="line"> <span class="keyword">if</span> daemon.saveApparmorConfig(container); err != <span class="literal">nil</span> {</span><br><span class="line"> <span class="keyword">return</span> err</span><br><span class="line"> }</span><br><span class="line">...</span><br><span class="line"> err = daemon.containerd.Create(context.Background(), container.ID, spec, createOptions)</span><br><span class="line"> <span class="keyword">if</span> err != <span class="literal">nil</span> {</span><br><span class="line"> <span class="keyword">return</span> translateContainerdStartErr(container.Path, container.SetExitCode, err)</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">// TODO(mlaventure): we need to specify checkpoint options here</span></span><br><span class="line"> pid, err := daemon.containerd.Start(context.Background(), container.ID, checkpointDir,</span><br><span class="line"> container.StreamConfig.Stdin() != <span class="literal">nil</span> || container.Config.Tty,</span><br><span class="line"> container.InitializeStdio)</span><br><span class="line">...</span><br><span class="line"></span><br><span class="line"> container.SetRunning(pid, <span class="literal">true</span>)</span><br><span class="line"> container.HasBeenManuallyStopped = <span class="literal">false</span></span><br><span class="line"> container.HasBeenStartedBefore = <span class="literal">true</span></span><br><span class="line"> daemon.setStateCounter(container)</span><br><span class="line"></span><br><span class="line"> daemon.initHealthMonitor(container)</span><br><span class="line">... </span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>這個函式非常的重要，可以看一下該函式的註解<br><div class="note danger">
<p>// containerStart prepares the container to run by setting up everything the<br>// container needs, such as storage and networking, as well as links<br>// between containers. The container is left waiting for a signal to<br>// begin running.</p>
</div></p>
<p>再這個函式內會創建好相關的容器，並且會將該容器用到的相關資源(儲存/網路)等都準備好<br>，由於我們要觀察的是 <code>DNS</code> 相關的資訊，所以我們要繼續往 <code>initializeNetworking</code> 的方向往下追。</p>
<h2 id="initializeNetworking"><a href="#initializeNetworking" class="headerlink" title="initializeNetworking"></a>initializeNetworking</h2><figure class="highlight go"><figcaption><span>initializeNetworking</span><a href="https://github.com/docker/docker-ce/blob/6e92e5909666b3b9c2aecebf582e8af85f228899/components/engine/daemon/container_operations.go#L916" target="_blank" rel="noopener">container_operations.go</a></figcaption><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></pre></td><td class="code"><pre><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">func</span> <span class="params">(daemon *Daemon)</span> <span class="title">initializeNetworking</span><span class="params">(container *container.Container)</span> <span class="title">error</span></span> {</span><br><span class="line"> <span class="keyword">var</span> err error</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> container.HostConfig.NetworkMode.IsContainer() {</span><br><span class="line">...</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> container.HostConfig.NetworkMode.IsHost() {</span><br><span class="line">...</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> err := daemon.allocateNetwork(container); err != <span class="literal">nil</span> {</span><br><span class="line"> <span class="keyword">return</span> err</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="keyword">return</span> container.BuildHostnameFile()</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>接下來都是根據各種 <code>Networking</code> 相關的設定來處理，前面兩個的判斷處理則是根據當初創建該容器時，有沒有指令 <code>--network=xxxx</code> 來特別處理，若有設定 <code>--network=host</code> 或是 <code>--network=container:xxxx</code> 會有一些額外的處理。</p>
<p>因為這些情境跟我們的 <code>Kubernetes</code> 的使用方法不同，我們不會走到這邊的判斷，而是直接會走到下面的 <code>allocateNetwork</code> 來開始準備網路相關的資訊。</p>
<h2 id="allocateNetwork"><a href="#allocateNetwork" class="headerlink" title="allocateNetwork"></a>allocateNetwork</h2><figure class="highlight go"><figcaption><span>allocateNetwork</span><a href="https://github.com/docker/docker-ce/blob/6e92e5909666b3b9c2aecebf582e8af85f228899/components/engine/daemon/container_operations.go#L501" target="_blank" rel="noopener">container_operations.go</a></figcaption><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></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">func</span> <span class="params">(daemon *Daemon)</span> <span class="title">allocateNetwork</span><span class="params">(container *container.Container)</span> <span class="title">error</span></span> {</span><br><span class="line">...</span><br><span class="line"></span><br><span class="line"> <span class="comment">// always connect default network first since only default</span></span><br><span class="line"> <span class="comment">// network mode support link and we need do some setting</span></span><br><span class="line"> <span class="comment">// on sandbox initialize for link, but the sandbox only be initialized</span></span><br><span class="line"> <span class="comment">// on first network connecting.</span></span><br><span class="line"> defaultNetName := runconfig.DefaultDaemonNetworkMode().NetworkName()</span><br><span class="line"> <span class="keyword">if</span> nConf, ok := container.NetworkSettings.Networks[defaultNetName]; ok {</span><br><span class="line"> cleanOperationalData(nConf)</span><br><span class="line"> <span class="keyword">if</span> err := daemon.connectToNetwork(container, defaultNetName, nConf.EndpointSettings, updateSettings); err != <span class="literal">nil</span> {</span><br><span class="line"> <span class="keyword">return</span> err</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> }</span><br><span class="line">...</span><br><span class="line"> <span class="keyword">return</span> <span class="literal">nil</span></span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>再這個函式內，首先會嘗試使用預設的網路型態，這邊指的就是在創建容器所下的參數 <code>--net=xxx</code>，而預設的類型就是 <code>bridge</code>.<br>所以接下來就很直覺的去呼叫 <code>connectToNetwork</code> 來進行下一階段的處理</p>
<h2 id="connectToNetwork"><a href="#connectToNetwork" class="headerlink" title="connectToNetwork"></a>connectToNetwork</h2><figure class="highlight go"><figcaption><span>connectToNetwork</span><a href="https://github.com/docker/docker-ce/blob/6e92e5909666b3b9c2aecebf582e8af85f228899/components/engine/daemon/container_operations.go#L690" target="_blank" rel="noopener">container_operations.go</a></figcaption><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></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">func</span> <span class="params">(daemon *Daemon)</span> <span class="title">connectToNetwork</span><span class="params">(container *container.Container, idOrName <span class="keyword">string</span>, endpointConfig *networktypes.EndpointSettings, updateSettings <span class="keyword">bool</span>)</span> <span class="params">(err error)</span></span> {</span><br><span class="line"> start := time.Now()</span><br><span class="line"> <span class="keyword">if</span> container.HostConfig.NetworkMode.IsContainer() {</span><br><span class="line"> <span class="keyword">return</span> runconfig.ErrConflictSharedNetwork</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">if</span> containertypes.NetworkMode(idOrName).IsBridge() &&</span><br><span class="line"> daemon.configStore.DisableBridge {</span><br><span class="line"> container.Config.NetworkDisabled = <span class="literal">true</span></span><br><span class="line"> <span class="keyword">return</span> <span class="literal">nil</span></span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line">....</span><br><span class="line"> sb := daemon.getNetworkSandbox(container)</span><br><span class="line"> createOptions, err := buildCreateEndpointOptions(container, n, endpointConfig, sb, daemon.configStore.DNS)</span><br><span class="line"> <span class="keyword">if</span> err != <span class="literal">nil</span> {</span><br><span class="line"> <span class="keyword">return</span> err</span><br><span class="line"> }</span><br><span class="line">....</span><br><span class="line"> <span class="keyword">if</span> sb == <span class="literal">nil</span> {</span><br><span class="line"> options, err := daemon.buildSandboxOptions(container)</span><br><span class="line"> <span class="keyword">if</span> err != <span class="literal">nil</span> {</span><br><span class="line"> <span class="keyword">return</span> err</span><br><span class="line"> }</span><br><span class="line"> sb, err = controller.NewSandbox(container.ID, options...)</span><br><span class="line"> <span class="keyword">if</span> err != <span class="literal">nil</span> {</span><br><span class="line"> <span class="keyword">return</span> err</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> updateSandboxNetworkSettings(container, sb)</span><br><span class="line"> }</span><br><span class="line">....</span><br><span class="line"> <span class="keyword">return</span> <span class="literal">nil</span></span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p><code>connectToNetwork</code> 並不是只有創建新的容器時才會使用，所以這邊還會進行一些相關的參數檢查。<br>由於我們是第一次串件該容器，所以容器所對應的沙盒 <code>SandBox</code> 會是空的。<br>最後根據空的沙盒，決定透過 <code>controller.NewSanbox</code> 去創建一個沙盒。<br>值得注意的是，這邊有一個 <code>buildSandboxOptions</code> 會把其他用到的參數都重新整理一次，然後傳入到 <code>controller.NewSandbox</code> 這邊去處理。</p>
<h2 id="NewSandbox"><a href="#NewSandbox" class="headerlink" title="NewSandbox"></a>NewSandbox</h2><figure class="highlight go"><figcaption><span>NewSandbox</span><a href="https://github.com/docker/libnetwork/blob/f30a35b091cc2a431ef9856c75c343f75bb5f2e2/controller.go#L1126" target="_blank" rel="noopener">controller.go</a></figcaption><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></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">func</span> <span class="params">(c *controller)</span> <span class="title">NewSandbox</span><span class="params">(containerID <span class="keyword">string</span>, options ...SandboxOption)</span> <span class="params">(Sandbox, error)</span></span> {</span><br><span class="line"> <span class="keyword">if</span> containerID == <span class="string">""</span> {</span><br><span class="line"> <span class="keyword">return</span> <span class="literal">nil</span>, types.BadRequestErrorf(<span class="string">"invalid container ID"</span>)</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="keyword">var</span> sb *sandbox</span><br><span class="line">...</span><br><span class="line"></span><br><span class="line"> <span class="comment">// Create sandbox and process options first. Key generation depends on an option</span></span><br><span class="line"> <span class="keyword">if</span> sb == <span class="literal">nil</span> {</span><br><span class="line"> sb = &sandbox{</span><br><span class="line"> id: sandboxID,</span><br><span class="line"> containerID: containerID,</span><br><span class="line"> endpoints: []*endpoint{},</span><br><span class="line"> epPriority: <span class="keyword">map</span>[<span class="keyword">string</span>]<span class="keyword">int</span>{},</span><br><span class="line"> populatedEndpoints: <span class="keyword">map</span>[<span class="keyword">string</span>]<span class="keyword">struct</span>{}{},</span><br><span class="line"> config: containerConfig{},</span><br><span class="line"> controller: c,</span><br><span class="line"> extDNS: []extDNSEntry{},</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> sb.processOptions(options...)</span><br><span class="line">...</span><br><span class="line"> <span class="keyword">if</span> err = sb.setupResolutionFiles(); err != <span class="literal">nil</span> {</span><br><span class="line"> <span class="keyword">return</span> <span class="literal">nil</span>, err</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> </span><br><span class="line"> <span class="keyword">return</span> sb, <span class="literal">nil</span></span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<div class="note danger">
<p>特別注意一下，當我們到這邊執行相關函式的時候，我們的專案已經從<code>docker-ce</code>遷移到<code>libnetwork</code>了。</p>
</div>
<p>這個函式非常的長，描述的創建新的 <code>Sandbox</code> 期間需要注意的所有事項，這邊首先會透過<code>sb.processOptions</code> 去設定相關變數的數值，這邊要特別注意的是其實每一個 <code>options</code> 本身是對應到一個 <code>function pointer</code>。</p>
<div class="note danger">
<p>如果我們當初有透過 <code>dockerd</code> 去設定相關的 <code>DNS</code> 設定的話，這邊其實實際上會賦值到 <code>sb.config.dnsList</code>, <code>sb.config.dnsSearchList</code> 以及 <code>sb.config.dnsOptionsList</code></p>
</div>
<figure class="highlight go"><figcaption><span>setupResolutionFiles</span><a href="https://github.com/docker/libnetwork/blob/c3a682c10b554b2ff2fac8ca134ddb9047ffdd93/sandbox_dns_unix.go#L61" target="_blank" rel="noopener">sandbox_dns_unix.go</a></figcaption><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></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">func</span> <span class="params">(sb *sandbox)</span> <span class="title">setupResolutionFiles</span><span class="params">()</span> <span class="title">error</span></span> {</span><br><span class="line"> <span class="keyword">if</span> err := sb.buildHostsFile(); err != <span class="literal">nil</span> {</span><br><span class="line"> <span class="keyword">return</span> err</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> err := sb.updateParentHosts(); err != <span class="literal">nil</span> {</span><br><span class="line"> <span class="keyword">return</span> err</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="keyword">return</span> sb.setupDNS()</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>這邊其實非常簡單，我們的主要目標終於出現了!!!<br><code>setupDNS</code> 意思就如同名稱一樣直接，就是設定該沙盒內<code>DNS</code>的設定。</p>
<h2 id="setupDNS"><a href="#setupDNS" class="headerlink" title="setupDNS"></a>setupDNS</h2><figure class="highlight go"><figcaption><span>setupDNS</span><a href="https://github.com/docker/libnetwork/blob/c3a682c10b554b2ff2fac8ca134ddb9047ffdd93/sandbox_dns_unix.go#L181" target="_blank" rel="noopener">sandbox_dns_unix.go</a></figcaption><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></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">func</span> <span class="params">(sb *sandbox)</span> <span class="title">setupDNS</span><span class="params">()</span> <span class="title">error</span></span> {</span><br><span class="line"> <span class="keyword">var</span> newRC *resolvconf.File</span><br><span class="line">....</span><br><span class="line"></span><br><span class="line"> originResolvConfPath := sb.config.originResolvConfPath</span><br><span class="line"> <span class="keyword">if</span> originResolvConfPath == <span class="string">""</span> {</span><br><span class="line"> <span class="comment">// if not specified fallback to default /etc/resolv.conf</span></span><br><span class="line"> originResolvConfPath = resolvconf.DefaultResolvConf</span><br><span class="line"> }</span><br><span class="line"> currRC, err := resolvconf.GetSpecific(originResolvConfPath)</span><br><span class="line"> <span class="keyword">if</span> err != <span class="literal">nil</span> {</span><br><span class="line"> <span class="keyword">if</span> !os.IsNotExist(err) {</span><br><span class="line"> <span class="keyword">return</span> err</span><br><span class="line"> }</span><br><span class="line"> <span class="comment">// it's ok to continue if /etc/resolv.conf doesn't exist, default resolvers (Google's Public DNS)</span></span><br><span class="line"> <span class="comment">// will be used</span></span><br><span class="line"> currRC = &resolvconf.File{}</span><br><span class="line"> logrus.Infof(<span class="string">"/etc/resolv.conf does not exist"</span>)</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> <span class="built_in">len</span>(sb.config.dnsList) > <span class="number">0</span> || <span class="built_in">len</span>(sb.config.dnsSearchList) > <span class="number">0</span> || <span class="built_in">len</span>(sb.config.dnsOptionsList) > <span class="number">0</span> {</span><br><span class="line"> <span class="keyword">var</span> (</span><br><span class="line"> err error</span><br><span class="line"> dnsList = resolvconf.GetNameservers(currRC.Content, types.IP)</span><br><span class="line"> dnsSearchList = resolvconf.GetSearchDomains(currRC.Content)</span><br><span class="line"> dnsOptionsList = resolvconf.GetOptions(currRC.Content)</span><br><span class="line"> )</span><br><span class="line"> <span class="keyword">if</span> <span class="built_in">len</span>(sb.config.dnsList) > <span class="number">0</span> {</span><br><span class="line"> dnsList = sb.config.dnsList</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">if</span> <span class="built_in">len</span>(sb.config.dnsSearchList) > <span class="number">0</span> {</span><br><span class="line"> dnsSearchList = sb.config.dnsSearchList</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">if</span> <span class="built_in">len</span>(sb.config.dnsOptionsList) > <span class="number">0</span> {</span><br><span class="line"> dnsOptionsList = sb.config.dnsOptionsList</span><br><span class="line"> }</span><br><span class="line"> newRC, err = resolvconf.Build(sb.config.resolvConfPath, dnsList, dnsSearchList, dnsOptionsList)</span><br><span class="line"> <span class="keyword">if</span> err != <span class="literal">nil</span> {</span><br><span class="line"> <span class="keyword">return</span> err</span><br><span class="line"> }</span><br><span class="line"> <span class="comment">// After building the resolv.conf from the user config save the</span></span><br><span class="line"> <span class="comment">// external resolvers in the sandbox. Note that --dns 127.0.0.x</span></span><br><span class="line"> <span class="comment">// config refers to the loopback in the container namespace</span></span><br><span class="line"> sb.setExternalResolvers(newRC.Content, types.IPv4, <span class="literal">false</span>)</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> <span class="comment">// If the host resolv.conf file has 127.0.0.x container should</span></span><br><span class="line"> <span class="comment">// use the host resolver for queries. This is supported by the</span></span><br><span class="line"> <span class="comment">// docker embedded DNS server. Hence save the external resolvers</span></span><br><span class="line"> <span class="comment">// before filtering it out.</span></span><br><span class="line"> sb.setExternalResolvers(currRC.Content, types.IPv4, <span class="literal">true</span>)</span><br><span class="line"></span><br><span class="line"> <span class="comment">// Replace any localhost/127.* (at this point we have no info about ipv6, pass it as true)</span></span><br><span class="line"> <span class="keyword">if</span> newRC, err = resolvconf.FilterResolvDNS(currRC.Content, <span class="literal">true</span>); err != <span class="literal">nil</span> {</span><br><span class="line"> <span class="keyword">return</span> err</span><br><span class="line"> }</span><br><span class="line"> <span class="comment">// No contention on container resolv.conf file at sandbox creation</span></span><br><span class="line"> <span class="keyword">if</span> err := ioutil.WriteFile(sb.config.resolvConfPath, newRC.Content, filePerm); err != <span class="literal">nil</span> {</span><br><span class="line"> <span class="keyword">return</span> types.InternalErrorf(<span class="string">"failed to write unhaltered resolv.conf file content when setting up dns for sandbox %s: %v"</span>, sb.ID(), err)</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">// Write hash</span></span><br><span class="line"> <span class="keyword">if</span> err := ioutil.WriteFile(sb.config.resolvConfHashFile, []<span class="keyword">byte</span>(newRC.Hash), filePerm); err != <span class="literal">nil</span> {</span><br><span class="line"> <span class="keyword">return</span> types.InternalErrorf(<span class="string">"failed to write resolv.conf hash file when setting up dns for sandbox %s: %v"</span>, sb.ID(), err)</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="keyword">return</span> <span class="literal">nil</span></span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>這個函式會針對一些跟 <code>DNS</code> 相關的參數來進行處理，包含了</p>
<ol>
<li>dnsServer</li>
<li>dnsSearch</li>
<li>dnsOptions</li>
<li>resolveConf</li>
</ol>
<p>這邊的運作邏輯如下</p>
<ol>
<li>先根據參數<code>resolveConf</code>來讀取當前 <code>DNS</code> 的全部設定</li>
<li>如果使用者有自行設定 <code>DNS</code> 的參數，就會全面使用這邊的設定，完全忽略(1)載入的設定<br>2.1 這邊最後會呼叫 <code>resolvconf.Build</code> 將參數的設定直接覆寫到容器內的 <code>/etc/resolv.conf</code></li>
<li>如果使用者沒有自行設定 <code>DNS</code> 的話，就會針對 (1) 載入的設定進行一次過濾<br>3.1 針對 127.0.0.1/8 之類的進行過濾 <code>FilterResolveDNS</code><br>3.2 過濾後若發現是空的，則補上 8.8.8.8/8.8.4.4</li>
</ol>
<p>這樣就來看一下 <code>FilterResolveDNS</code> 怎麼處理 <code>DNS</code></p>
<h2 id="FilterResolveDNS"><a href="#FilterResolveDNS" class="headerlink" title="FilterResolveDNS"></a>FilterResolveDNS</h2><figure class="highlight plain"><figcaption><span>https://github.com/docker/libnetwork/blob/c3a682c10b554b2ff2fac8ca134ddb9047ffdd93/resolvconf/resolvconf.go resolvconf.go</span></figcaption><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></pre></td><td class="code"><pre><span class="line"></span><br><span class="line">// FilterResolvDNS cleans up the config in resolvConf. It has two main jobs:</span><br><span class="line">// 1. It looks for localhost (127.*|::1) entries in the provided</span><br><span class="line">// resolv.conf, removing local nameserver entries, and, if the resulting</span><br><span class="line">// cleaned config has no defined nameservers left, adds default DNS entries</span><br><span class="line">// 2. Given the caller provides the enable/disable state of IPv6, the filter</span><br><span class="line">// code will remove all IPv6 nameservers if it is not enabled for containers</span><br><span class="line">//</span><br><span class="line">func FilterResolvDNS(resolvConf []byte, ipv6Enabled bool) (*File, error) {</span><br><span class="line"> cleanedResolvConf := localhostNSRegexp.ReplaceAll(resolvConf, []byte{})</span><br><span class="line"> // if IPv6 is not enabled, also clean out any IPv6 address nameserver</span><br><span class="line"> if !ipv6Enabled {</span><br><span class="line"> cleanedResolvConf = nsIPv6Regexp.ReplaceAll(cleanedResolvConf, []byte{})</span><br><span class="line"> }</span><br><span class="line"> // if the resulting resolvConf has no more nameservers defined, add appropriate</span><br><span class="line"> // default DNS servers for IPv4 and (optionally) IPv6</span><br><span class="line"> if len(GetNameservers(cleanedResolvConf, types.IP)) == 0 {</span><br><span class="line"> logrus.Infof("No non-localhost DNS nameservers are left in resolv.conf. Using default external servers: %v", defaultIPv4Dns)</span><br><span class="line"> dns := defaultIPv4Dns</span><br><span class="line"> if ipv6Enabled {</span><br><span class="line"> logrus.Infof("IPv6 enabled; Adding default IPv6 external servers: %v", defaultIPv6Dns)</span><br><span class="line"> dns = append(dns, defaultIPv6Dns...)</span><br><span class="line"> }</span><br><span class="line"> cleanedResolvConf = append(cleanedResolvConf, []byte("\n"+strings.Join(dns, "\n"))...)</span><br><span class="line"> }</span><br><span class="line"> hash, err := ioutils.HashData(bytes.NewReader(cleanedResolvConf))</span><br><span class="line"> if err != nil {</span><br><span class="line"> return nil, err</span><br><span class="line"> }</span><br><span class="line"> return &File{Content: cleanedResolvConf, Hash: hash}, nil</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<ul>
<li>首先先呼叫 <code>ReplaceAll</code> 把所有 <code>localhost 127.0.0.0/8</code> 相關的 <code>IP</code> 都清空。</li>
<li>清空之後，若發現這時候沒有 <code>DNS</code> 的話，直接透過 <code>dns := defaultIPv4Dns</code> 補上預設的 <code>DNS</code> (8.8.8.8/8.8.4.4)</li>
</ul>
<h1 id="summary"><a href="#summary" class="headerlink" title="summary"></a>summary</h1><p>當每次創建新容器時，最後會依賴到 <code>libnetwork</code> 內跟 <code>DNS</code> 相關的參數來設定</p>
<ol>
<li>如果使用者有自行設定 <code>DNS</code> 的參數，就會全面使用這邊的設定，完全忽略(1)載入的設定<ul>
<li>這邊最後會呼叫 <code>resolvconf.Build</code> 將參數的設定直接覆寫到容器內的 <code>/etc/resolv.conf</code></li>
</ul>
</li>
<li>如果使用者沒有自行設定 <code>DNS</code> 的話，就會針對 (1) 載入的設定進行一次過濾<ul>
<li>針對 127.0.0.1/8 之類的進行過濾 <code>FilterResolveDNS</code></li>
<li>過濾後若發現是空的，則補上 8.8.8.8/8.8.4.4</li>
</ul>
</li>
</ol>
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